The Illusion of Ambiguity: from Bistable Perception to

fiammetta ghedini

T H E I L L U S I O N O F A M B I G U I T Y: F R O MB I S TA B L E P E R C E P T I O N T O

A N T H R O P O M O R P H I S M

T H E I L L U S I O N O F A M B I G U I T Y: F R O M B I S TA B L EP E R C E P T I O N T O A N T H R O P O M O R P H I S M

fiammetta ghedini

A dissertation submitted in partial fulfilment of the requirements forthe degree of Doctor in Philosophy in Innovative Technologies of

Information and Communication Engineering and Robotics

30 May 2011

Fiammetta Ghedini: The Illusion of Ambiguity: from Bistable Per-ception to Anthropomorphism, A dissertation submitted in par-tial fulfilment of the requirements for the degree of Doctorin Philosophy in Innovative Technologies of Information andCommunication Engineering and Robotics, © 30 May 2011

No lesson of psychology is perhaps more important for thehistorian to absorb than this multiplicity of layers, the peaceful

coexistence in man of incompatible attitudes.

— Sir Ernest Gombrich

There is an universal tendency among mankind to conceive allbeings like themselves, and to transfer to every object, thosequalities, with which they are familiarly acquainted, and of

which they are intimately conscious.

— David Hume

A B S T R A C T

This thesis is a multidisciplinary work at the merging of neuro-science, art and human interaction with technologies. Its objec-tives are:

1. Review the literature and further investigate, by means ofa brain imaging study, which are the mechanisms allow-ing the illusion of ambiguity in the brain, by proposing aframework of analysis based on different levels of ambigu-ity;

2. Discuss the concept of the illusion of life, defined as a per-ceptual phenomenon included into the wider category ofambiguity and caused by intentionality and animacy beinghard-wired in the brain (part of that previous knowledgenecessary to successfully process sensory inputs);

3. Explore features in behaviour and form which are mostlikely to trigger anthropomorphism, drawing insights fromart, technological applications and cognitive sciences, andfocusing on human interaction with artificial creatures.

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P U B L I C AT I O N S

Some ideas and figures have appeared previously in the follow-ing publications:

Perception of Ambiguous Figures: an fMRI study, F. Ghedini& M.Bergamasco, VRR-IJCAI 2011, 18-24 July, Barcelona, Spain[Ghedini and Bergamasco, 2011b]

Life evocation in art: from representation to behaviour. F. Ghe-dini & M.Bergamasco, ISEA 2011, 12-16 September, Instanbul,Turkey [Ghedini and Bergamasco, 2011a]

Robotic Art: Perceiving and inventing reality. F. Ghedini &M.Bergamasco, Art and Science: exploring the limits of humanperception, Conference Proceedings, Benasque, Spain, on July12-16, 2009 [Ghedini and Bergamasco, 2009]

"Passages: An Artistic 3D Interface for Children’s Rehabilita-tion and Special Needs" F. Ghedini, H. Faste, M. Carrozzino, M.Bergamasco ICDVRAT International Conference Series on Dis-ability, Virtual Reality, and Associated Technologies, Portugal,09-08-2008 [Ghedini et al., 2008]

Robotic expression. Developing an applied framework for theintegration of artistic approaches and technological competences,2008, PhD Application for the Scuola Superiore Sant’Anna [Ghe-dini, 2008]

A conversation with Bill Vorn (on robotic art creatures andother believable living machines) Scuola Superiore Sant’Anna,Pisa, Italy, 09-17-2007[Vorn, 2007]

"Enactive Network of Excellence, Digest 2006: MultimodalInterfaces," Massimo Bergamasco, Fiammetta Ghedini, HaakonFaste, Editors Enactive Consortium Press, project IST-2004-002114-ENACTIVE, 02-15-2007

Haptic interaction with virtual sculptures, 2007 MassimoBergamasco, Marcello Carrozzino, Fiammetta Ghedini

"Enaction and Inactive Interfaces: A Handbook of Terms,"Enactive Systems Books, 2007

"Le interfacce aptiche per i Beni Culturali" M. Bergamasco,C.A. Avizzano, F. Ghedini, M. Carrozzino Proceedings of LUBEC2007, "Valorizzazione dei Beni Culturali e Innovazione", Lucca,Italy, 2008 ISBN 978-88-89766-10-1 [Bergamasco et al., 2007]

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A C K N O W L E D G M E N T S

This dissertation would not have been possible without the sup-port and encouragement of Professor Massimo Bergamasco, myPh.D. supervisor at Perceptual Robotics Laboratory of ScuolaSuperiore Sant’Anna. Throughout my thesis he provided guid-ance, advices and inspiration. I would like to thanks all thecolleagues with whom I had the pleasure of collaborating: CarloAlberto Avizzano, Franco Tecchia, Antonio Frisoli, Chiara Evan-gelista, Elisabetta Sani, Federico Vanni, Walter Aprile, AndreaBizdideanu, Vittorio Spina, Davide Vercelli, Rosario Leonardi,Paolo Tripicchio, Paolo Gasparello, Emanuele Giorgi; VittorioLippi and Emanuele Ruffaldi for their precious help with LateXand those other colleagues whom I have neglected to mention.A special thanks to Haakon Faste for his inspiring enthusiasmand eclectic skills, Marcello Carrozzino for providing usefulfeedback and to Francesca Farinelli and Alessandra Scucces forbeing not only helpful colleagues but also very dear friends,and for supporting me during my thesis-writing period. Mygratefulness goes also to all the people working in the adminis-tration of the Scuola Sant’Anna and especially Laura Bevacqua.For enlightening conversations, encouragement, feedback andinspiration I would like to thank Israel Rosenfield. I owe a lot tohim and to his perspectives on neuroscience. I also would liketo thank Simon Penny and Bill Vorn for visiting our Laboratoryand inspiring me with their artworks on artificial life. My deep-est gratefulness goes to Professor Semir Zeki who made possiblethe fMRI experiment described in this thesis. Thank you for yourguidance and for working with me for over one year at the Well-come Lab of Neurobiology at UCL, London. I am indebted to allthe people working in Professor Zeki’s lab: Barbara Nordhjemfor her continuous support, John Romaya for his experience, JonStutters for his skills, Shelley Tootell for her helpfulness andTomohiro Ishizu and Sam Cheadle for being always supportive,through difficult times too. Thanks for you friendship and kind-ness. Thanks to all the people from the academic world who inconferences, seminars and workshops provided new inspiringideas, feedback on my research and good company: Mel Slater,Mavi Sanchez, Doron Friedman, Peggy Weil, Nonny de la Pena,Marcelo Wanderlay, Elena Pasquinelli, Benoit Bardy and many

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others. A very special thanks goes to Tommaso Andreussi: youwill print your next book on Luoyang paper! Finally, "merci"to François Pachet for his encouragement, for being a modelof what a researcher should be, and most importantly for com-ing into my life. And "grazie" to my parents, Anna Casanovaand Fabio Ghedini, because they taught me the importance ofknowledge: to them I dedicate my thesis.

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C O N T E N T S

i introduction 111 introduction 13

1.1 Perception: Making Sense of the Senses . . . . . . 141.1.1 Watching without seeing . . . . . . . . . . . 151.1.2 The Brain: an Abstraction Machine . . . . . 171.1.3 The Case of Colour Vision . . . . . . . . . . 19

1.2 Concepts and Categories in the Brain . . . . . . . 221.3 Seeing through Illusions . . . . . . . . . . . . . . . 24

1.3.1 Two Different Categories of Illusions . . . . 241.3.2 Ambiguity and Ambiguities . . . . . . . . . 27

ii first and second level ambiguity 312 perception of bistable ambiguity 33

2.1 What is multistable ambiguity . . . . . . . . . . . . 332.1.1 Neural processes underlying multistable

phenomena . . . . . . . . . . . . . . . . . . 362.1.2 Attention and perception of bistable figures 412.1.3 Levels of ambiguity . . . . . . . . . . . . . . 42

2.2 An Experiment on Two-Levels Bistable Ambiguity 422.2.1 General fMRI Analysis . . . . . . . . . . . . 46

2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . 482.3.1 Behavioural results . . . . . . . . . . . . . . 48

2.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . 502.4.1 Conclusion . . . . . . . . . . . . . . . . . . . 53

iii third level ambiguity 613 third level ambiguity : the illusion of life 63

3.1 Perceptual knowledge of life . . . . . . . . . . . . . 633.2 The illusion of intentionality . . . . . . . . . . . . . 663.3 The illusion of life in the brain . . . . . . . . . . . 69

3.3.1 Emotional clues in the illusion of life . . . 72

iv forth level ambiguity 754 aesthetics of anthropomorphism 77

4.0.2 Anthropomorphism as a forth level ambi-guity . . . . . . . . . . . . . . . . . . . . . . 77

4.0.3 Variability in anthropomorphisation . . . . 774.1 Life evocation in the arts . . . . . . . . . . . . . . . 78

4.1.1 Defining life away . . . . . . . . . . . . . . . 78

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xiv contents

4.1.2 Art and the illusion of life . . . . . . . . . . 794.1.3 From art to technology . . . . . . . . . . . . 834.1.4 Uncanniness as a result of life evocation . . 84

4.2 The illusion of life in artificial creatures: featuresof believability . . . . . . . . . . . . . . . . . . . . . 854.2.1 Form: is realism a necessity? . . . . . . . . 86

4.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . 90

bibliography 95

L I S T O F F I G U R E S

Figure 1.1 The response of an orientation selective cell 18Figure 1.2 The response of an orientation selective

cell in V5 . . . . . . . . . . . . . . . . . . . . 19Figure 1.3 A rotation of a mask: the forth image shows

the inside of the mask, appearing convexeven if it is hollow . . . . . . . . . . . . . . 25

Figure 1.4 Model of perception, based on (Gregory2009) . . . . . . . . . . . . . . . . . . . . . . 27

Figure 1.5 Different kinds of ambiguities . . . . . . . . 29Figure 2.1 a) Necker Cube - b) Rubin Vase . . . . . . . 34Figure 2.2 Binocular rivalry . . . . . . . . . . . . . . . 35Figure 2.3 Auditory streaming is a case of multistable

perception in the auditory modality . . . . 36Figure 2.4 Experiment stimuli: bistable intra-categorical

images + stabilized versions . . . . . . . . . 54Figure 2.5 Experiment stimuli: bistable inter-categorical

images + stabilized versions . . . . . . . . . 55Figure 2.6 Bistable Figures > Stable Figures . . . . . . 56Figure 2.7 Global 3D view of activations for the con-

trast internal change > external change fora random effects analysis with 16 subjects:selected activations superimposed on toaveraged anatomical sections . . . . . . . . 57

Figure 2.8 T statistic for Bistable > Stable in conjunc-tion with Intra-categorical: Bistable > Sta-ble switches (left) and Inter-categorical:Bistable > Stable switches (right) . . . . . . 57

Figure 2.9 Bistable activations conjoined with Inter-categorical and intra-categorical bistableactivations . . . . . . . . . . . . . . . . . . . 58

Figure 2.10 Bistable faces > All. FFA activation pro-jected onto averaged structural scans (left)and main HRF and TD plotted for FFA [38-58 -14] (right) . . . . . . . . . . . . . . . . 59

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xvi List of Figures

Figure 4.1 The Uncanny Valley graph following Mori 85

Part I

I N T R O D U C T I O N

1I N T R O D U C T I O N

From bistableperception toanthropomorphism

This thesis is a multidisciplinary work, whose goal is to mergeinsights and research from fields as different as art, neuroscienceand technology. My original question was: how do we attributefeatures of animacy (such as emotions and intentions) to objects,in spite of the certain knowledge of their non-animacy? Thisquestion brought me to consider, in the first place, some basicphenomena of perception, and in particular, illusions. Illusionsmake evident that perception is not a passive mapping of in-puts coming from the environment, but an active interpretation,involving a mechanism of inference. As illustrated in Chapter I,studies on optical illusions may be very useful in order to revealthe active role of the brain in the organisation of perceptualprocesses. Among all different kinds of illusion, ambiguity isone of the most interesting, since it clarifies how our brain dis-ambiguates the information received. Ambiguity is traditionallydefined as an alternation in time of two mutually exclusive inter-pretations of the same stimulus [Zeki, 2004]. As I propose in theframework of this thesis, this definition fits to a specific kind ofambiguity, namely the "intra-categorical" one, taking place whenthe two possible interpretations of the same stimulus belongto the same semantic category, for example the two recessionalplanes of the Necker cube. This kind of ambiguity is the basicmodel of a mechanism that probably happens endlessly in ourbrain, since our everyday environment contains ambiguitiesand conflicts which we do not usually notice because our brainsuccessfully - and continuously - disambiguates them. It can behypothesised that such an evaluation process is occurring allthe time, but becomes evident when ambiguities are maximised,as in the case of ambiguous stimuli. Indeed, also multistableambiguity involves a continuous and frequent evaluation ofsensory inputs, but it results in puzzling flips (or reversals) inperception, since ambiguous percepts do not provide enoughclues for "deciding" which is the "good" interpretation. But, inpartial contrast with the above quoted traditional definition, Ido not consider all possible interpretations of an ambiguousimage as mutually excluding. In Chapter II, on the basis ofbrain imaging data, I will propose the notion of different levels

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14 introduction

of ambiguity, including in such a framework the concepts of theillusion of life and of life evocation as "higher level" ambiguities.The illusion of life is a phenomenon that can be consideredas the perceptual basis of anthropomorphising, or attributinganimacy, emotions, intentionality, personality and other traitscommon to living agents to non-animated stimuli. The illusionof life takes place when geometrical stimuli showing certainfeatures of motion and behavior automatically elicit attributionof animacy and intention, as investigated in the seminal studiesof [Michotte, 1946] and [Heider and Simmel, 1944]. While theillusion of life is automatically and universally perceived, withthe only exception of persons with very specific brain damages,anthropomorphising is a psychological tendency implying anindividual variability and depending on factors such as socialisolation and need of mastering the environment. In Chapter IIII will focus on the features and neural events underlying theillusion of life, outlining why it can be considered as an illusionof ambiguity. As illustrated in Chapter IV, perception of animacyof non-animated objects has always been exploited and exploredby artists, who have been featuring in their works the aestheticsof life evocation. Finally, life evocation triggering anthropomor-phising has a great potential of application in today’s society,where humans interact more and more with technological ob-jects such as robots and avatars, designed to embody believablecreatures. In Chapter IV I will discuss some features of animacyperception drawing inspiration from arts and insights from thecognitive sciences, with the objective of outlining believabilityissues for the design of technological applications.

1.1 perception: making sense of the senses

Perception as anactive process Philosophy and science have traditionally separated intelligence

from perception, vision being interpreted as a passive windowson the world. It was German fellow Hemann von Helmholtz(1821-1894) who first proposed the principle that visual percep-tions are unconscious inferences [von Helmholtz, 1962]. VonHelmholtz thought that human perception is only indirectlyrelated to objects, being inferred from fragmentary data. Therehave been researchers who maintained a "direct" theory of per-ception, notable American psychologist J. Gibson [Gibson, 1950]who outlined the theory of affordances, proposing a model inwhich our senses "pick up" information form the environmentgiving significance to pattern of stimulation without recurring

1.1 perception: making sense of the senses 15

to further processing. But the majority of studies today agree onthe hypothesis that perception is not a passive reception of theinformation coming from the surrounding environment, ratheraffirming that the brain is a story-teller who actively buildsthe reality surrounding us, as illustrated by [Rosenfield, 1988].Researchers point out that our senses are faced by a chaotic, per-sistently changing world without labels. What our brain activelydoes is organising external reality, allowing us to generaliseand thus use the information we need from the environment,imbuing it with meaning. Since meaning is not in things butis in the brain, information, if not interpreted by the brain, isempty of meaning.

1.1.1 Watching without seeing

The born-blind issueResearchers supporting the thesis of "active perception" often re-fer to the argument of born-blind people regaining sight duringadulthood. Indeed, born-blid individuals who recuperated theirsight after many years, even if visually perceiving objects, donot "see" them (they do not understand what the objects are), orlearn to do it after a long and difficult training. In this brain con-dition, generally labelled as agnosia, sensations of light, colour,movement and shape can reach the brain but are meaningless;therefore for individuals suffering from this condition, objectsare seen as "meaningless" items. The first debate about this topiccan be traced back to a correspondence between English philoso-pher John Locke and William Molyneaux [Gregory, 1987]. In1688 the Irish scientist and politician William Molyneux (1656–1698) sent a letter to John Locke in which he asked whethera man who has been born blind and, during the course of hislife, has learnt to distinguish and name a cube and a sphereby touch, would be able to distinguish and name these objectssimply by sight, once he had been enabled to see. The so-called"Molyneaux problem" has been solved forty years later, whenthe English surgeon William Chelsden operated a 13 years oldfrom a cataract, allowing the boy to see for the first time in hislife. The first impression of the boy was objects were "dispropor-tioned". Moreover he did not have any sense of distance, and ofthe relation between size and distance: a little object very closeto his eyes was equivalent to a big house seen from far away. Hewas not able to distinguish a cat from a dog, unless he couldtouch them.

16 introduction

a case of sight recovery When he first saw, Cheseldenwrites, he was so far from making any judgement of dis-tances, that he thought all object whatever touched hiseyes (as he expressed it) as what he felt did his skin, andthought no object so agreeable as those which were smoothand regular, though he could form no judgement of theirshape, or guess what it was in any object that was pleasingto him: he knew not the shape of anything, nor any onething from another, however different in shape or magni-tude; but upon being told what things were, whose formhe knew before from feeling, he would carefully observe,that he might know them again; and (as he said) at firstlearned to know, and again forgot a thousand things in aday. One particular only, though it might appear trifling,I will relate: Having often forgot which was the cat, andwhich the dog, he was ashamed to ask; but catching thecat, which he knew by feeling, he was observed to lookat her steadfastly, and then, setting her down, said, So,puss, I shall know you another time. He was very muchsurprised, that those things which he had liked best, didnot appear most agreeable to his eyes, expecting thosepersons would appear most beautiful that he loved most,and such things to be most agreeable to his sight, that wereso to his taste. We thought he soon knew what picturesrepresented, which were shewed to him, but we foundafterwards we were mistaken; for about two months afterhe was couched, he discovered at once they representedsolid bodies, when to that time he considered them only asparty-coloured planes, or surfaces diversified with varietyof paint; but even then he was no less surprised, expectingthe pictures would feel like the things they represented,and was amazed when he found those parts, which bytheir light and shadow appeared now round and uneven,felt only flat like the rest, and asked which was the lyingsense, feeling or seeing? [Cheselden, 1683-1775]

The boy thus had a troublesome learning path, in which noth-ing came natural or spontaneous; he was conscious of the effortand he was trying to learn and record things everyday. For in-stance, he knew that he had a cat and a dog, and that he hadto distinguish them by seeing them; this task was probably asdifficult as for a normal-sighted person learn to distinguish at aglance two very similar specimen of the same breed. But, tridi-mensionality appeared to Cheselden’s patient as some kind of


illusion. Even after he acquired the capacity to correctly interpretbidimensional images, he was still "amazed" to perceive thebody represented by paintings as flat. The phenomenon thanksto which he could see a bidimensional object as tridimensionalwas so obscure to him that he was convinced that one of hissensory channels must have being lying. Several similar oper-ations have been conducted afterwards, and always with thesame results. In particular, bidimensional representations are al-ways troubling for born-blind individuals recovering their sight,because they see such representations in three dimensions, andthey cannot understand how this can be, when they touch theimage finding it flat. "Normal" perception of size, distance andtridimensionality is a phenomenon that we take for granted -but is actually the result of an operation of abstraction producedby the brain.

1.1.2 The Brain: an Abstraction Machine

Distance, size and tridimensionality are abstractions producedby the brain among all the mechanisms allowing us to recog- Abstraction at cell

levelnise objects. Acquiring the capacity to create the abstraction of"representation on two dimensions" is probably something thatwe learn to do very early in time, and blind born individualsdo not have the possibility to develop at "due time". Studiesaffirm that the common capacity of the cerebral cortex - whethervisual, auditory, somato-sensory ot otherwise- is namely theone of abstraction: "the capacity to abstract seems to accompany,and to be a corollary of, every specificity" [Zeki, 2009]. What itis meant for abstraction, in this specific context, is the capacityto grasp a general property instead of the particular one. Anexample of this process at a single cell level is orientation se-lectivity [Hubel and Wiesel, 1977]. Orientation selectivity is theproperty of some cells in the visual brain, which respond toobjects (lines) of a specific orientation and do not respond tolines oriented orthogonally at their "preferred" orientation: thereare cells which will respond only to vertical lines, and otherto horizontal ones. For instance, a vertical-selective cell willrespond when the stimulus is vertical, without being concernedwith what is vertical, whether a tree or a vertical line or a tower:this means that the cell has abstracted the property of verticalityfrom different stimuli discarding individual specificities.

In Figure 1.1, we can see the reponse of an orientation selectivecell. Such a response can be studied by inserting an electrode

18 introduction

Figure 1.1: The response of an orientation selective cell

into the visual cortex (a) and showing bars of light of differentorientation into the Receptive Field (the small rectangle on theleft, RF), that is to say that part of the global visual field (thebigger rectangle) which will trigger an electrical discharge in thestudied cell. (b) shows the representation of the cell’s selectivityto orientation: the cell responds positively to the oblique linemoved in two opposite directions (first three records) while itis unresponsive to the orthogonal orientation. In the same way,cells of the brain area specialised for processing motion, V5, aredirectionally selective. This means that they respond to motionin a specific direction and not in the opposite one, as illustratedin Figure 1.2. This kind of abstraction does not concern exclu-sively the visual brain, but also other sensory modalities. Cells"designed" for perceiving pressure in the somatosensory cortexwill respond to pressure independently from what causes it; thesame thing is true for a cell responding to temperature, pain,and for the auditory system.


Figure 1.2: The response of an orientation selective cell in V5

1.1.3 The Case of Colour Vision

Abstraction is the strategy used by the brain in order to create acoherent environment out of a chaotic and ever-changing world.As in the largely discussed example of colour vision, we cannot What are colours?help but perceive and organise constant features; we cannotavoid seeing a leaf as green at dawn and dusk, or a rose as redboth in a sunny and cloudy day, taking for granted that "colours"are features intrinsic to objects. Since the world we see is alwayschanging and the retina receives a constant flow of differentkinds of visual information, the brain must be able to selectvisual properties of objects and surfaces in order to give themmeaning. In acquiring this ability, the brain has developed spe-cialized functions for the analysis of different properties, suchas colour, shape, and movement. For example, contrary to ourvisual experience, there are no colours in the world, only elec-tromagnetic waves of many frequencies. Our retinal receptorsfor colour are divided in three categories, responding optimallyto long (red), middle (green), and short (blue) wavelengths. Thebrain compares the amount of light reflected in the wavelengths,and from these comparisons creates the colours we see. Theamount of light reflected by a particular surface - a table, forexample - depends on the frequency and the intensity of the

20 introduction

light hitting the surface; some surfaces reflect more short-wavefrequencies, others more long-wave frequencies; but the par-ticular sensation produced by a specific colour is created byour brain. Indeed, if our perception of an object as red were tochange with every change in the wavelength of light reflectedfrom it, the object would constantly change in appearance. If wewere aware of our ’real’ visual worlds we would see constantlychanging images of dirty grey - constantly changing images thatwould be very confusing, often making it impossible for us tosee forms. While, thanks to this mechanism, the brain is ableto attribute a constant colour making itself largely independentof the amount of light of the waveband reflected from objects’surfaces. This mechanism is a way of our brain of "inventing" anattribute allowing us to identify objects by means of a constantand meaningful feature. How can this happen in the brain? VonHelmholtz [von Helmholtz, 1962] based this phenomenon onlearning: he thought that since we know that a leaf is green,we operate a mechanism, which he names "unconscious infer-ence", allowing to "attribute" a colour to the leaf even if theilluminant (the wavelength composition of the light reflected indifferent lighting conditions) always changes. Another Germanpsychophysicist, Ewald Hering, thought that memory playeda central role [Hering, 1964 (originally pub. 1877]. Higher cog-nitive functions have therefore always been addressed whentrying to explain mechanisms underlying colour vision, untilEdwin Land (the inventor of the Polaroid) finally proposedanother point of view [Land, 1974]. He hypothesised that theassignment of constant colours to objects is the result of a sim-ple computational process of the brain, due to some kind ofinnate capacity of organisation of visual signals. Following Land,colours are the result of the comparison between the amount oflight of different wavebands reflected from a surface and fromits surrounds. This comparison has as a result a ratio, which isconstant (differently from the amount of reflected light).The Land hypothesis

the inherited concept of ratio-taking: In the Landexperiment, a green surface is surrounded by yellow, redand blue surfaces. If the surface is lighten by a projectorprojecting blue light, the surface will reflect let’s say 60units (milliwatts) of green light. The surrounds will bereflecting less green light. The same surface is seen undera red light: the green surface will now reflect 30 units ofgreen light. But we will still see it as green! This is be-cause the surrounding surfaces will reflect even less units


of green light than before. Indeed, the ratio (relationshipbetween the amount of green light reflected by the greensurface and the one reflected by non-green surfaces) isalways identical.

Colour perception is the most powerful example of how ourexperience of the world is based on the brain’s capacity toperform operations related to inherited concepts rather thenmere physical reality. The crucial feature of the colour system inthe brain is the ability to ascribe a constant colour to an objectdespite of wide-ranging changes in the wavelengths-energy com-position of the light reflected by such an object. If the colour ofthe surface would change along with every change in its lightingenvironment, objects would have ever-changing surfaces (e.g.,leafs would be green in the morning and red in the evening).This mean that colours would not mean much and, rather thanprovide us with information about things, would actually con-fuse us, being a non-constant overflow of useless information.The importance of understanding colour as a construction ofthe brain is that colour is an example of mechanism that thebrain has developed through evolution, and that concurs toinstil meaning and thus gain additional knowledge from theenvironment: our visual worlds are stabilized because the brain,through colour perception, simplifies the environment by com-paring the amounts of lightness and darkness in the differentfrequencies from one moment to the other. In the same way,an object maintains its identity independently from the pointof view and distance we look at it. The capability to organizeconstantly changing stimuli in a stable and meaningful way isan impressive feature of perception and is the way our brainallows us to cope with reality. And just as colours are differentin kind from the images projected on our retinas, space anddepth are different in kind from the individual images projectedthe retinas of our eyes. In creating three-dimensionality anddepth the brain in actually invents subjective experience. Thethree-dimensionality we normally see is not part of the "real"world; all of our perceptions are from a particular point of viewand that individual point of view is our subjectivity; it is cre-ated by the brain as it makes sense of the physical world thatsurrounds us.

22 introduction

1.2 concepts and categories in the brain

We saw how the brain can be independent from the continualchange of the surrounding information, allowing us to recognizeessential and non-changing characteristics of objects and situa-tions, optimising knowledge acquisition by abstraction. Colourperception is an example of categorisation intrinsic to the brain’sdesign. The capacity to see colours can be lost, as happenedto the most famous case of cerebral achromatopsia, the one ofthe colour-blind painter Johnathan I. [Sacks, 1995]. But, evenif the capacity to see colours stays intact, the brain can losethe capacity to abstract; and in this case, even if colours are"viewed", they are not "understood", becoming useless. Gelband Goldstein [Gelb and Goldstein, 1925] have reported the caseof a patient who was incapable to define the colours of objects,even if, apparently, he could perceive them. The patient couldnot indicate the name of the colour of an object mentioned tohim, neither he was able to point out a colour correspondingto a colour-name. Presented with colour samples, he utteredsome names, giving the impression that words had no meaning.When he was asked to choose a red object among a sample ofdifferent objects, he would choose by chance. But, if he was re-quested to chose a colour sample fitting to a coloured object, healways succeed: he never chose a wrong colour. On the contrary,he was never satisfied: if the colour specimen did not matchperfectly with the colour of the object, he continued looking fora more fitting specimen. This proved that he could "perceive"colours. But, when the patient had to assort different specimenof colours, the patient was incapable to find a unifying categoryin order to group them: the factor of hue, brightness, or otherfactors may prevail. Gelb and Goldstein explained the patient’sCategorising

behaviour behaviour (as well as other patients symptoms) as effects of thereduction from the level of "categorical" behaviour to the level of"concrete" behaviour. Confronted with the same task (groupingcolour specimina according to hue) the normal person imme-diately assorts the same specimina, e.g. a very light and a verydark red, by categorizing them as "red". In doing so, she is notunaware of the difference between them; she is performing anoperation of abstraction (abstracting the "redness") and categori-sation (by discarding "individual" differences among speciminaand unifying under the category "red"). Gelb and Goldstein’spatient, even seeing colours, was unable to establish abstractrelations between the category (red, blue, green, etc.) and the

1.2 concepts and categories in the brain 23

concrete colour. When he was asked to define the colours, healways had to make a comparison (e. g. "like an orange, like acherry") and he was meticulously grouping colours but withoutbacking up on a categorical sense. The patient was confined tothe content of perception as it is actually experienced (he wasseeing the "real" world, in a way); in other words he could notgo through his perceptual experience under the perspective ofa principle external to the perceptual experience itself, beingunable to refer his actual experience to any conceptual order.In the framework of this regression to a "concrete" behaviour,there is no hierarchy or differentiation between the experientialfeatures and their significance. All features are equally impor-tant; each features is of paramount importance because all ofthem are encountered "at the same level" in actual perception.The patient was overwhelmed by the actual experience, and hecould not emancipate from it by imposing a structure able tocreate meaning in the world.

What Goldstein refers to as "categorising" behaviour is par-allel to Zeki’s theory of inherited and acquired concepts: "The Inherited and

acquired conceptsinherited concepts organize the signals coming into the brain soas to instil meaning into them and thus make sense of them",[Zeki, 2009] while acquired concepts are generated through-out our existence, with the goal of simplifying perceiving andrecognizing things and situations. Inherited brain concepts areidentifiable by three features, in Zeki’s view: absence of freewill, immutability and autonomy. Therefore, in this perspectivecolour perception may be classified as an inherited concept, sincewe can not choose what colours we perceive, nor we can chooseof seeing the "real" colours of things instead that the colours"invented" by our brain; secondly, our system of perception forcolours is immutable, does not change over years - in normalconditions - and thirdly, the generation of colours is dependenton a specialised cortical system that differs from other systemsdesigned for processing other kinds of visual features. Whileacquired concepts are a way to organise knowledge throughoutour life (for instance, we can learn to define a specific set ofpaintings as "still life" and we will be able to insert in such a cat-egory all still life that we will see afterwards, even if they will becomposed of different objects, lighting conditions, colours, etc.).Still, what acquired and inherited concepts have in common isthe capacity of the brain to abstract and to generalize.

24 introduction

1.3 seeing through illusions

The way in which our brain organises knowledge can be more ef-ficiently investigated in exceptional conditions: those situationsin which things do not work as usual. This means analysingthose circumstances in which the brain’s capacity of stabilisationand abstraction is invalidated, temporary or permanently dis-carded, as in the cases of brain damages and illusions [Gregory,2009]. It is hard to give a satisfactory definition of the term "il-lusion". The OED (Oxford English Dictionary) defines it as "aninstance of a wrong or misinterpreted perception of a sensoryexperience"; here I will refer more precisely, to those phenom-ena implying a discrepancy measurements and inner perception.Such a discrepancy can happen when the knowledge (inheritedor acquired) that we "superimpose" to perception is inappro-priate or misapplied; in other words, where the "assumptions"we are doing are wrong. Indeed, perception is - following thisperspective - based on inferences that we deduce from sensorysignals; being an inference, it requires a previous knowledge.This is why illusions can clarify many mechanisms behind per-ception, indicating where and how this "previous knowledge"(abstraction, categories and things we learn throughout our life)play a role. As Chelsden’s blind born boy asked himself whetherwas the sight or the touch which was lying: he thought thatperceived tridimensionality was an illusion. And in a way itis, because behind our capacity to view tridimensional imagesin pictures there is a level of abstraction: illusions can provideevidence of working rules of perception.

1.3.1 Two Different Categories of Illusions

Physical illusionsGregory identifies two different kinds of illusion, the cognitiveand the physical ones. While the latter ones have a physicalcause, cognitive illusions are due following Gregory to "misap-plication of knowledge" employed by the brain in interpretingsensory signals [Gregory, 2009]. Illusions due to the disturbanceof light, between objects and the eyes, are different from illu-sions due to the disturbance of sensory signals of eye, thoughboth might be classified as physical. Among these, we can listwith Gregory mist (loss of information increasing uncertainty),mirage (refraction of light between the object and the eyes dis-placing objects or parts of objects, rainbow. Discussing this

1.3 seeing through illusions 25

taxonomy is nevertheless outside the scope of this thesis, andfor further reading on this subject we remand to [Gregory, 2009]. Cognitive illusions

Cognitive illusions are further devided by Gregory into "spe-cific knowledge" of objects from "general knowledge". An exam-ple of specific knowledge cognitive illusion is the "hollow face"illusion.

Figure 1.3: A rotation of a mask: the forth image shows the inside ofthe mask, appearing convex even if it is hollow

As illustrated in Figure 1.3, when seeing a hollow mask weare strongly biased in seeing it as convex. This bias of seeingmasks as convex is so strong it competes with monocular depthcues, such as shading and shadows, and also very considerableunambiguous information from the two eyes signalling stereo-scopically that the perceived object is hollow. Also, a textureimitating wood could look like wood even if it is plastic, or if it ispainted; this is because we apply our specific knowledge to thetexture and make an inference about the material on the basisof a specific and repeated experience (wood is grainy, brownish,etc.). An example of general knowledge leading to cognitiveillusions is misleading rules of Gestalt (Wertheimer, 1923/1938)applied to tricky objects (designed to trigger the illusion) e. g.Kanitsa triangle, due to postulating a nearer occluding surface to

26 introduction

explain "surprising" gaps [Gregory, 1972]. General knowledge,in this case, is the rules of Gestalt (closure, proximity, continuity,common fate) singled out by Wertheimer and influencing ourvision of objects (independently from the objects themselves).In order to trigger illusion related to misapplication of generalknowledge it is necessary to investigate the perception of excep-tional and atypical objects. For Gregory [Gregory, 1972] this isthe evidence of top-down knowledge applied to perception: thismeans that since we know, due to our experience, that faces -and therefore masks - are generally convex, we perceive it assuch. The top-down knowledge applied to this experience isvery strong, and even if we know that the mask is hollow, we seeit as convex. Interestingly, patients affected by schizophrenia donot perceive this illusion [Schneider et al., 1996]. This may meanthat they are more inclined to top-down influences since theyare affected by a lack of connectivity: Dima [Dima et al., 2009]demonstrated that schizophrenic patients show an increasedactivity of bottom-up processes if compared to healthy controls,who do perceive the hollow face illusion; schizophrenic subjectsin this sense see the world "as it really is" relying on stimulus-driven processes. On the basis of this perspective on illusions asA model of

perception a model of perception is illustrated in Figure 1.4: perception isan hypothesis, or an inference in Von Helmotz’s defition [vonHelmholtz, 1962] coming from a continuous dialogue of signalprocessing, perceptual and conceptual knowledge. Signals fromthe senses (bottom-up) are not only influenced (top-down) bypre-existing knowledge (e.g.: faces are convex) but also by per-ceptual "rules", which constitute the "language of the brain" (e.g. Gestalt rules, colour view); this continuous loop gives rise toqualia, sensations about what we perceive.

What is typical of several illusions is that they are experiencedperceptually though the observer knows conceptually that they areillusions. This phenomenon can tell us something interestingAutomaticity of

illusions about the nature of knowledge that we superimpose to percep-tion. It is not "conceptual" knowledge, but it is a separated kindof knowledge, that could be defined as "perceptual knowledge".This perceptual knowledge is probably linked to evolution al-lowing perceptual mechanisms to work very fast and efficiently,this being useful in case of danger. Perceptual knowledge is theassumptions that our brain takes, and can coexist with concep-tual knowledge even when in contradiction, as in the case ofseveral illusions. Also, if perceptual knowledge would not bedifferent from conceptual knowledge, our beliefs would deter-


Figure 1.4: Model of perception, based on (Gregory 2009)

mine perception making us blind to the new or strange, whichwould be dangerous in unusual situations, and would limitperceptual learning. What is this previous knowledge? For vonHelmoltz, signal processing interpretation is resolved thanksto previous knowledge by unconscious inductive inference. Aswe saw above, Zeki [Zeki, 2009] declines this definition in in-herited and acquired concepts, granting the brain a grasp onthe world (but also demanding a "prize to pay" when misap-plied). Gregory [Gregory, 2009] organises "previous knowledge"in general knowledge and specific knowledge, proposing thatperceptions are hypothesis predicting "unsensed characteristics"of the objects. I will use the term "conceptual knowledge" for in-dicating top down higher cognitive knowledge and "perceptualknowledge" for indicating bottom up impressions that can, asinvestigated in the next chapters, overcome and/or coexist withconceptual knowledge.

1.3.2 Ambiguity and Ambiguities

Among different illusions, it is especially the phenomenon ofambiguity that make us think of perception as actively creative:indeed, it makes clear that some kind of interpretation and

28 introduction

previous knowledge is necessary. Ambiguity, understood as itA general definitionis defined in the OED ("ambiguous: uncertain, open to morethan one interpretation, of doubtful position") is a feature ofthe environment that our brain faces every day, since it is con-fronted with situations or views that are open to more thanone interpretations. Retinal images are inherently ambiguous(for example for size, shape and distance of objects), but alsolanguage, situations, sounds. If, on the basis of the above modelFour levels of

ambiguity of perception, interpretations are hypothesis, thus, ambiguitymeans openness to two or more alternative hypothesis. Suchhypothesis can be mutually excluding in the instant but co-existing over time, or just coexisting. This thesis will explorethe hypothesis of different levels of ambiguity, on the basis ofthe possibilities of different interpretation to be mutually exclu-sive, partially or totally coexist. In certain cases, as the abovediscussed case of colour vision, the "choice" among interpre-tation is relatively simple, since it is limited by the design ofthe brain. It becomes more complex in other cases, when nosingle solution is more likely than other possible solutions. Eachinterpretation becomes as valid as the other interpretations, andthere is no correct interpretation. As illustrated in Figure 1.5,I will propose a framework of analysis identifying four levelsof ambiguity, whose first two levels are illustrated in ChapterII as results of a brain imaging study on neural bistability. InChapter III I will introduce the concept of "illusion of life", as athird level ambiguity, in which two possible interpretations arecoexisting in the conscious stage of the qualia but not mutuallyexcluding; the illusion of life always coexist with the awarenessof the non-animacy of the stimuli; nevertheless, such an illusionis automatically and universally perceived (except for patientswith specific brain damages). Going further, we could identifya phenomenon of ambiguity in anthropomorphism, in whichthe concept of individual variability has to be introduced (cfr.Chapter IV).


Figure 1.5: Different kinds of ambiguities

Part II

F I R S T A N D S E C O N D L E V E LA M B I G U I T Y

2P E R C E P T I O N O F B I S TA B L E A M B I G U I T Y

This chapter will discuss literature about how and where am-biguous perception takes place in the brain, and why ambiguityis a crucial issue for understanding how the mind works andhow do we gather information from the surrounding environ-ment. It will also discuss the results of an fMRI experimentcarried out in the general framework of ambiguity with a focuson visual bistability, proposing a framework of analysis basedon multiple levels of ambiguity, which takes into account thatdifferent interpretations of the stimulus content may not only ex-clude each other, but also coexist, depending on different levelsof ambiguity.

2.1 what is multistable ambiguity

Bistable ambiguous images are puzzling because they can bespontaneously experienced as two equally valid percepts. Fol-lowing the model of perception illustrated in Chapter I, whenthe brain is confronted with an ambiguous stimulus perceptualknowledge is oscillating between two different interpretation,while conceptual knowledge is aware that the percept is notactually changing. Following the literature, during the so-calledbistability illusion, the brain is confronted with one ambiguousstimulus that can be stably interpreted in only one way at anygiven moment, but will present two possible interpretationsover time; in other words, a stimulus is ambiguous when it isconsistent with two or more mutually exclusive interpretations[Zeki, 2004].

Repeated viewing of ambiguous stimuli lead to spontaneousperceptual switches, or "flips", where the brain alternates be-tween two or more stable perceptual interpretations every fewseconds. Multistable ambiguity is an especially interesting il-lusion because it can help us understand the mechanisms gen-erating a meaningful and coherent experience of the world,even though the the information we have is fragmentary andambiguous. Visual illusions of ambiguity are actually a sortor quintessential and simplified model of the choices that ourbrain is confronted with everyday, and in every modality. Some

33

34 perception of bistable ambiguity

Figure 2.1: a) Necker Cube - b) Rubin Vase

of the most well-know ambiguous figures are the Necker cubeand the Rubin vase (Figure 2.1). The perceptual interpretationof the Necker cube oscillates between two different recessionalplanes, while the interpretation of the Rubin vase alternatesbetween one vase and two profiles. Ambiguity is present alsoin other perceptual phenomena, namely bistable apparent mo-tion and binocular rivalry (Figure 2.2). Binocular rivalry resultsBinocular rivalryfrom presentation of different images to each eye, thanks to adispositive separating the view of one eye to the other one. Theresult is bistable alternation between the two images: the subjectis conscious of one stimulus at the time, and the perception isincessantly fluctuating between the two stimuli. For instance,the subject represented in Figure 2.2, looking at the vertical lineswith his left eye and looking at the horizontal lines with hisright eye will cyclically perceive only vertical lines alternatingwith only horizontal lines.

Multistable perception (when the possible interpretations areAuditorymultistability more than two) can characterise the auditory modality as well,

in the form of auditory stream segregation [Bregman, 1990] andverbal transformation effect [Warren and Gregory, 1958]. Audi-tory stream segregation happens when two tones of a differentfrequency are presented alternately in a repeating temporal pat-tern, as illustrated in Figure 2.3. Subjects’ perception alternatesbetween interpreting the sequence either as one stream withfluctuating tones or as two segregated streams (in the picture,indicated by the grey thick line).Verbal

transformation effect Verbal transformation effect occurs when a word is cycledin continuous repetition [Warren and Gregory, 1958] like for

2.1 what is multistable ambiguity 35

Figure 2.2: Binocular rivalry

instance the word "life". Initially, a percept corresponding to theoriginal form prevails, but after a certain period another percepttakes over and it stably alternates with the original one: in thecase of the repeated word "life", at a certain point the subjectwill perceive the word "fly" alternating with "life". Ambiguity in

languageAmbiguity is also a feature of many sentences, which canmean two very different things, being in a way "bistable" and in-terpretable only by means of the context in which they are used.There is a distinction between vagueness and real ambiguity:truly "bistable" sentences are the ones whose "meaning" can flipand can be stabilized only by context, for instance. "People likeus" [Gregory, 2000] or "She can’t bear children". Tactile ambiguity

Bistability exist also in the modality of touch, even if it hasto be triggered artificially. A tactile illusion has been devel-oped by Carter et al [Carter et al., 2008]. By means of a devicedesigned to provide the subject with vibrotactile stimuli, theresearchers could lead participants to report switches betweenthe perception of motion directed either up and down or leftand right across their fingertip, while the sensory input due tothe vibrotactile device stayed unvaried.

Nevertheless, visual ambiguity is undoubtedly the most stud-ied phenomenon among all these. Indeed, ambiguous figureshave become an experimental tool to study interpretive cognitiveprocesses related to conscious awareness because the perceptualexperience alternates over time without any external changes ofthe stimuli [Leopold and Logothetis, 1999]; [Sterzer et al., 2009].


Figure 2.3: Auditory streaming is a case of multistable perception inthe auditory modality

In particular, interest in this field has been growing thanks to theadvent of non-invasive brain imaging techniques such as fMRI(functional magnetic resonance imaging), which is the techniqueused for the experiment described further on.

2.1.1 Neural processes underlying multistable phenomena

Even tough perception of ambiguous figures has been exten-sively studied, there are many contradicting findings and contro-Top-down vs

bottom-up versies. Traditionally, two main theories explain why ambiguousfigures reverse; the main distinction is between supporters of thecentral role of bottom-up versus top-down processes [Leopoldand Logothetis, 1999]. The bottom-up theory proposes that neu-rons maintaining one percept fatigue over time and give rise toneurons supporting the other percept; the switch should thusbe independent from high-level (cognitive) control. Accordingto the top-down theory, ambiguous figures do not switch spon-taneously: the preconditions for seeing reversals are that theviewer knows the figure is bistable, knows the possible inter-pretations of the figure, and switches are initiated by intention.There are experimental findings supporting both theories, thus


more recent studies have adopted an hybrid model explicat-ing bistability as the result of a continuous dialogue betweenbottom-up and top-down processes [Toppino and Long, 2005][Mitroff et al., 2006]

Concerning the localisation in the brain where bistable am-biguity takes place, several studies show that changes in earlyvisual activity precedes conscious changes of perception. Thanks Subcortical and

early cortical visualprocessing

to fMRI studies, it has been consistently demonstrated that binoc-ular rivarly strongly effects V1, the earliest visual processingarea [Polonsky et al., 2000], [Tong and Engel, 2001] [Lee, 2005]. AMEG study [Parkkonen et al., 2008] shows that early visual brainareas (V1 and V2) reflect how an ambiguous figure is perceived,both for binocular rivalry and for Rubin’s vase. Also activity inprimary visual cortex recorded with EEG could predict whatperspective is perceived even before a geometrical ambiguousfigure was presented [Kornmeier and Bach, 2005]. This studydemonstrated that perceived reversal of perspective was pre-ceded by 160 ms with negativity in primary visual cortex. Asimilar negative component was found 50 ms earlier doing theexperiment with a stabilized version of the figure. fMRI studieshave also shown that activity not only in V1 but also in anotherpost-retinal processing area, the LGN (lateral geniculate nucleus)reflects the perceptual outcome of binocular rivalry [Tong et al.,2006]. These experiments alone could support the bottom-upthesis, that is to say the hypothesis that perception of ambigu-ous figures is resolved in a feed-forward manner by primarysensory areas without the involvement of higher cognitive areas;but, since there is evidence also for top-down processes, thisdata can be interpreted as a proof that early visual processingstages including V1 and LGN are the prerequisite for consciousinterpretation of percepts. In any case, the role of this earlyvisual areas is that of processing information but also influenceinterpretation ("am I going to see a vase or a face?") either vialocal interactions or through modulation by feedback signalsfrom higher cognitive areas [Tong, 2003]. Evidence for the latterhypothesis comes from fMRI experiments on bistable apparentmotion. Indeed, whenever the perception of apparent motion isinconsistent with added clues, early visual activity is suppressed[Sterzer and Kleinschmidt, 2005].

Most studies agree on the role of the extrastriate cortex in Extrastriate visualcortexperceiving multistable ambiguities (extrastriate visual cortex

includes those areas lying beyond V1). Many fMRI studies re-vealed correlations between subjective perception and activity


in the functionally specialised extrastriate cortex, that is to say,areas specialised to process a certain type of information, re-flecting the "content" of the stimulus itself. fMRI studies (see[Sterzer et al., 2009] for a review) demonstrated that duringbinocular rivalry, fluctuations in signals in extrastriate cortexare similar to those during actual alternation of two differentstimuli, suggesting that the interpretation of ambiguous stimuliare fully resolved at the stage of processing, without maintain-ing a representation of the temporally suppressed stimulus.Actually, perception of binocular rivalry is influenced by infor-mation linked to the suppressed stimulus as well [Andrewsand Blakemore, 1999] indicating that the suppressed stimulusis somehow "present" and processed in the brain. For instance,the emotional content of a suppressed stimulus (e. g. a fearfulface) is still processed in the amygdala [Jiang and He, 2006],[Williams, 2004], where activity is expected when the stimulusis consciously perceived. A more recent and high resolutionfMRI study has also found activities corresponding to responsesto different object category in "houses versus faces" binocularrivalry, namely activations in the fusiform face area (FFA) andin the parahippocampal place area (PPA) even during binocularsuppression of one of the two categories of stimuli [Sterzer et al.,2008]; in the same way, face-specific responses are reduced butstill present in EEG during a face-suppression period [Sterzeret al., 2009]. In parallel with these findings on binocular rivalry,studies on ambiguous motion and bistable images confirm thatactivity in the extrastriate visual areas correlates with consciousperception, and also that those areas are involved in the cycli-cal resolution of ambiguities. Following [Andrews et al., 2002]and [Hasson et al., 2001], signals from FFA are greater duringthe perception of two faces in the Rubin vase-face illusion; andfollowing the same principle, a bistable illusion whose elementscan be perceived either as a coherent shape or as a randomstructure, will correlate with lateral occipital complex (LOC,which preferably activates processing objects) activations whenthe stimulus is perceived as coherent. In the case of ambiguousapparent motion versus flicker, the conscious perception of mo-tion will correlates with activations in V5 (area which processesmotion) while the conscious perception of flicker will not.

Another line of research has been focusing not on the per-ceptual states between one conscious perception and the otherNeural correlates of

flips one, but on the flips themselves, in other words neural eventscorrelating with perceptual reversals. Flips-related activity is


generally observed in extrastriate visual areas and it is associ-ated with activations tuned to the features of the percept that isperceived. For instance, perceptual reversals from faces to objectcorrelates with activations in the ventral stream [Leopold andLogothetis, 1999] while apparent changes in motion directioncorrelates with activation in V5, motion sensitive area. [Sterzerand Kleinschmidt, 2007] suggested that prefrontal areas set offchanges in perception of ambiguous motion. In an fMRI studythey used both ambiguous and unambiguous moving dots; acti-vation in right inferior frontal cortex appeared earlier than V5activation in both conditions. Moreover, the frontal activationhappened earlier for spontaneous flips when looking at am-biguous stimuli, compared to when a flip was stimulus driven.By using EEG, [Britz et al., 2009] were able to predict stimulusperception in a similar manner to Kornmeier and Bach (2004),they found significant increase of activity in right inferior pari-etal cortex 50 ms before a flip in perception occurred. It hasalso been demonstrated that activity in the FFA can be used topredict whether faces or a vase is perceived during presentationof the Rubin figure [Hesselmann et al., 2008]. Indeed, activityin the FFA is higher when subjects subsequently report perceiv-ing two faces instead of a vase, suggesting that pre-stimulusneural activity precede subsequent perceptual inference. Suchactivations suggest that ongoing brain activity influences theresolution of ambiguity before stimulus driven processes, anda key role of functionally specialised areas in processing andinterpreting conscious visual perception. Parietal, frontal and

prefrontal cortexfMRI activations correlated with perceptual reverals or flipsare also assessed in the parietal and frontal areas [Lumer et al.,1998]. While extrastriate areas are equally activated both bynon-ambiguous and by ambiguous stimuli, parietal and pre-frontal regions show higher levels of activity during ambiguityillusions [Lumer et al., 1998]. Such special activations in frontaland prefrontal cortex could suggest top-down mechanisms trig-gering a re-organisation of activity in the primary sensory areasduring flips as in [Leopold and Logothetis, 1999]. Or, from thebottom-up perspective, they could reflect the feed-forward com-munication of events from the earlier visual cortex to highercognitive areas, a sort of initiating gateway for further pro-cessing. For example, changes in apparent motion perceptionshow that activations of the prefrontal cortex precede that ofV5 for bistable motion perception [Sterzer and Kleinschmidt,2007]. This "initiating" role is corroborated by other findings,


drawn from a study suggesting that flips during observation ofa Necker cube are preceded by activations in the right parietalcortex [Britz et al., 2009]. In such a framework, it is noteworththat many people are able to control flips of bistable figures,which suggest that perception is also influenced by top-downfactors. For instance, participants were able to voluntarily in-crease or suppress the frequency of switches for the Neckercube [Tracy et al., 2005]. It is demonstrated that higher cognitiveareas have an effect on voluntary switches. Indeed, the abilityto voluntarily increase switches is diminished in frontal cortex-damaged patients; but, the same patients did not experience asignificantly different rate of reversals when flips where happen-ing spontaneously [Windmann et al., 2006], while research ofeffects of meditation consistently demonstrate that meditatorscan alter the normal fluctuations in conscious state induced bybinocular rivalry [Carter et al., 2005]. The role of frontal cortexin active switches suggests that top down influence may not benecessary, but higher cognitive areas can play a role voluntarilyinitiation changes, while alternation during passive viewing isless dependent on prefrontal cortex. Activities in frontal andparietal cortex is not only associated with flips, but also inpercept stabilisation. Indeed, the tendency of an individual tostabilize a percept during, for instance, periods in which thestimulus has been removed, is correlated with activations in thefrontal and parietals areas [Raemaekers, 2009].Bottom up versus

top down:conclusions

In conclusion, experimental findings neither support a puretop-down or bottom-up account. There is both support for re-versals driven by primary visual areas, processing specific areassuch as the FFA and parietal and frontal regions. Even thoughactivations in typical higher cognitive areas appear to be relatedto perceptual switches [Kleinschmidt et al., 1998]; [Lumer et al.,1998]; [Sterzer et al., 2002] their involvement is still debatable.[Zeki, 2004] argues that the frontoparietal network is involvedwhen there is a change in perception, without being involvedin the actual visual percept. One solution to the contrastingexperimental findings is that there might be interaction betweenhigher cognitive and primary sensory regions. Indeed, recentstudies do not point to either a purely top-down or bottom-upmodel. For instance, [Britz et al., 2009] found that activationin right inferior parietal cortex precedes the flips, while [Ko-rnmeier and Bach, 2005] were able to predict perception fromactivation in primary visual cortex. Also behavioural findingsseem to contrast a purely cognitive top-down account. It is true


that subjects who are not informed that a picture is ambiguousdo not always experience reversals, but evidence supports thatperceptual bistability be spontaneously experienced by childrenas young as 5 years [Mitroff et al., 2006].

2.1.2 Attention and perception of bistable figures

The overlap between areas involved in spatial attention andperception of bistable figures have lead to speculation about therole of attention processes, suggesting that frontoparietal regions The attention issuecould activate when re-directing attention to sensory input andre-initiate an evaluation of the current interpretation, leadingeither to maintain stable the current interpretation or change it.[Slotnick et al., 2003] found common neural activation for bothvoluntary shifts of attention and voluntary perceptual reversals.Since perceptual reversals usually occur spontaneously there hasbeen some debate about the exact role of the frontoparietal net-work [Sterzer et al., 2009]. Areas involved in voluntary attentionmay serve several functions, such as being engaged in feedbackto the sensory areas and perform an ongoing re-evaluation orthe visual experience [Leopold and Logothetis, 1999]. Anothersuggestion is that ambiguous information is detected in earlysensory areas activates the frontoparietal network, which shiftsattention between the possible versions over time. Accordingto the so-called focal-feature hypothesis, local areas within anambiguous figure favour different global interpretations. Neckerhimself (quoted in [Toppino, 2003] proposed that reversals aredriven by eye movements. Perception of the Necker cube can bebiased by moving the point of fixation during viewing [Petersonand Gibson, 1991]; [Toppino, 2003], and similar effect has beenfound other bistable figures as well [Tsal and Kolbet, 1985]. Alsofree viewing conditions support that eye gaze and perception ofthe Necker cube is closely linked [Einhauser et al., 2004]. After aswitch, the eye position also shifts. The authors suggest that thechanges of eye position serves as a negative feedback signal tosuppress the previous percept. [Leopold and Logothetis, 1999]propose that the same motor processes underlie both selectiveattention and bistable perception, and that there in most cases isa close coupling between saccades and percept switches. Chang-ing eye gaze and perceptual reversals could both reflect the waywe actively explore and constantly reinterpret the stimuli. It mayhowever be possible to alternate bistable figures without eyemovements.


To sum up, while previous studies opposed top-down [Leopoldand Logothetis, 1999] to bottom-up [Attneave, 1971], [Blake,1989] models, now multistable illusion is considered as a con-tinuous and frequent dialogue between low-level (sensorial)and high-level (parietal and frontal) areas, aiming to verify intime interpretation of stimuli (and initiating changes in percep-tion). There may be a relation between selective attention andperception of bistable figures, but this still needs to be clarified.

2.1.3 Levels of ambiguity

In his essay "The Neurology of Ambiguity" [Zeki, 2004] dis-tinguishes between different levels of ambiguity, introducinga new component in a discussion traditionally limited to thebottom-up/top-down approach. Zeki proposes that ambiguityhas different layers, or levels, which correlate with the neuralactivity in one or more processing regions with a consciouscorrelate. Following Zeki, figures like the Necker cube belongto the most simple form of ambiguity because brain activityremains within the same area over time, with the same neuralcorrelates for both states it can be experienced. At a higherlevel of ambiguity such as the Rubin figure, several processingareas are involved and the current perceptual state becomesconscious by fluctuation of neural activity between these areas.The Necker cube is always seen as a cube, while some imagesfluctuate between image categories such as the Rubin figure.On a much more sophisticated level, artwork such as Vermeer’spaintings are ambiguous in terms of narrative interpretation.Zeki’s differentiation between levels of ambiguities is rootedin his theory of ’microconsciousness’, where consciousness isseen as distributed over functionally specialized processing sitesin the brain, which give rise to consciousness without furtherhigher interpretation. The level of ambiguity can be definedat fluctuations within one or between several microconsciousstates.

2.2 an experiment on two-levels bistable ambiguity

In the work reported here, to investigate if there are generalpatterns of neural activations when looking at bistable figures,we compared perception of bistable images, where the physicalstimulus remains the same but perception alternates betweentwo interpretations, with perception of two externally alternat-

2.2 an experiment on two-levels bistable ambiguity 43

ing stable images. Subjects were instructed to repetitively reporttheir conscious experience of the visual stimuli by key-presses,reporting the occurrence of perceptual endogenous reversalsand the occurrence of actual reversals of stable percepts during a"replay condition". Based on previous research we hypothesizedincreased activation in the ventral occipital cortex, in parietal ar-eas, as well as in frontal areas during bistable stimuli comparedwith stable stimuli [Ilg et al., 2008]; [Kleinschmidt et al., 1998];[Lumer et al., 1998]; [Sterzer et al., 2002].

Further we wanted to test the theory of levels of ambigu-ity, verifying if perception of figures with different levels ofambiguity engage different brain areas. To compare levels of Levels of ambiguityambiguity we used two types of bistable images. We definethose images where perceptual flip takes place within the samecategory as "intra-categorical". This is the case for the Neckercube (Figure 2.1 a). Here, what appears to be in the front canoccupy a different recessional plane with prolonged viewing,but nevertheless it conceptually remains the same figure. Thiscontrasts with what we refer to as "inter-categorical", namelythe two images created by a single picture belong to differentcategories, as in the face- vase bistable image (Figure 2.1 b). Wedefine as "intra–categorical" those images in which the percep-tual flip takes place within the same category. In the presentstudy, inter-categorical stimuli alternates between bodies andfaces, since studies have demonstrated the selectivity of differentbrain regions to the visual representation of faces [Kanwisherand Yovel, 2006] and bodies [Peelen and Downing, 2007]. Wecompared how neural activity during perception of bistableintra-categorical images and bistable inter-categorical imagescontributed to the overall activations during perception of allbistable figures. To our knowledge, this is the first imagingstudy comparing two levels of ambiguity. In line with [Zeki,2004] above quoted theory we expected more involvement ofhigher cognitive areas for the ambiguous inter-categorical im-ages. As a third approach, we also addressed how brain activityfluctuates over time, and if transient patterns of activation arerelated to the type of images perceived. We investigated if sepa- Content of the

perceptrate neural mechanisms are involved in the transition from onepercept to another. The goal was to investigate if two perceptsbelonging to the same attribute or category, for example the tworecessional planes of the Necker cube, evoke different areas ofactivation compared to when the transition is from one categoryto another, as in the Rubin face-vase bistable image. We looked


at neural activation during alternating percepts for both intra-and inter-categorical figures. We hypothesized that same brainarea would be active when the translation would take placewithin images belonging to the same category, while areas ofactivation would change when the two percepts belong to twodifferent categories. Based on previous findings, we further hy-pothesized that during reported face perception the FFA wouldrespond stronger [Andrews et al., 2002]; [Hasson et al., 2001];[Tong et al., 1998], while the same areas would be active whenthe translation would take place within images belonging to thesame category.

Design: We used bistable images to separate, and thereforeExperimental designcompare, perceptual from stimulus-driven changes. In our study,subjects were requested to repetitively report by key-pressestheir conscious experience of flips during the observation ofbistable figures. Their responses were recorded and the sub-jective occurrence of perceptual reversals was replayed by al-ternating the two stabilized versions of the same percepts. Weused two sets of bistable images: intra-categorical and inter-categorical. Subjects were instructed, when looking at "geomet-rical figures" (intra–categorical stimuli) to alternate key presseswhen spontaneously perceiving a flip. For the inter–categoricalambiguous figures, subjects were requested to press a specifickey indicating body perception and another key indicating faceperception. During the replay condition, subjects were presentedwith stabilised versions of the ambiguous figures. The onsets ofthe alternating stabilised pictures were the same as when sub-jects indicated seeing a flip in the ambiguous condition. Subjectswere also requested to perform key presses during the replaycondition, in order to control for motor responses.

Subjects: 16 healthy subjects (with normal or corrected tonormal vision; 8 females) were recruited through advertisementsrequesting volunteers for a study about optical illusions. Theirage varied from 21 to 40 years (mean 29,8 years). Two subjectswere left handed. Informed written consent was obtained fromall participants and the study was covered by the MinimumRisk Ethics (Minimum risk magnetic resonance imaging studiesof healthy human cognition, UCL Ethics Project ID number:1825/003 / Data protection ref: Z6364106/2010/03/04). Duringa first visit to the laboratory, prior to scanning, each subjectwas requested to do a pre-test in order to qualify for the fMRIexperiment, by performing the same task to be carried out inthe scanner. X participants were excluded because they were not


able to perform the task correctly. During each scanning sessionsubject’s heart-rate and respiration were continuously recorded,providing physiological measurements to be subsequently usedas regressors-of-no-interest in the first-level SPM analysis foreach subject.

Stimuli: Stimuli were generated using Cogent 2000 and Co-gent Graphics (http://www.vislab.ucl.ac.uk/cogent.php). Fourintra-categorical images were chosen from the images in ThePsychophysics of Form: Reversible-Perspective Drawings of Spa-tial Objects, Hochberg and Brooks, The American Journal ofPsychology, Vol. 73, No. 3 (Sep., 1960), pp. 337-354, University ofIllinois Press) and 1 was created manually. Images were selectedfollowing a pre-test in which four subjects viewed 8 images andchose the ones that most easily flipped between two states forall subjects. All five intra-categorical ambiguous images weregenerated using Adobe InDesign CS3. Five inter–categorical im-ages were chosen from existing ambiguous figures. The choseninter–categorical images were those displaying two mutuallyexclusive interpretation, a body OR a face. Subsequently, eachambiguous image was modified to create two stable versions,which could be shown successively to the subjects using Photo-shop CS3, and two stable versions of each image were created(see Figures 2.4 and 2.5 ).

Each subject was exposed to two runs displaying the sameimages in the same order. Each run began with a neutral back-ground, lasting 26 s, during which the first six brain volumeswere discarded to allow T1 equilibration effects to subside. Thestimulus sequence then began. During each session the 10 am-biguous images (5 intra–categorical + 5 inter–categorical) weredisplayed; subjects were instructed to alternate key presseswhen perceiving a flip from one percept to the other. Withinter–categorical ambiguous images, subjects were instructedto press a button to indicate whether it was a body or a facethat they perceived. During each session, ambiguous imageswere mixed with a following replay condition of the subjects’perception, displaying the two alternating stabilised versions ofeach ambiguous image. The replay condition was implementedusing the recorded button presses relative to each ambiguousimage so that the time sequences remained the same. Conse-quently, the onsets of the alternating stabilised pictures werethe same as the alternating perceptual flips indicated by thesubjects. In order to control for motion correction, subjects werealso required to press buttons during the replay condition, each


time that the image changed. Each epoch lasted 16 s with aninter—stimulus interval varying in duration between 3 and 5s between stimuli where a blank grey screen was presented.Stimuli were presented in a pseudo-random sequence, ensuringthat each ambiguous image was presented before its stabilizedversions.

Scanning details: Scans were acquired using a 1.5–T SiemensMagneton Sonata MRI scanner fitted with a head volume coil(Siemens, Erlangen, Germany) to which an angled mirror wasattached, allowing subjects to view a screen onto which stimuliwere projected using an LCD projector. An echo-planar imag-ing (EPI) sequence was applied for functional scans, measuringBOLD signals (echo time TE =50 ms, repeat time TR= 90 ms,volume time 4.32 s). Each brain image was acquired in a de-scending sequence comprising 48 axial slices covering the wholebrain. The experiment consisted of 2 runs; 100 volumes were ac-quired per run. After functional scanning had been completed,a T1* weighted anatomical scan was acquired in the sagittalplane to obtain a high resolution structural image (176 slices pervolume).

2.2.1 General fMRI Analysis

Analysis: Data were analysed using SPM8 (http://www.fil.ion.ucl.ac.uk/SPM).The time series of functional brain volume images for each sub-ject was realigned and normalized into MNI space (voxel size3 x 3 x 3 mm) and then smoothed using a Gaussian smooth-ing kernel of 9 mm. The stimulus for each subject was mod-elled as a set of regressors in the SPM8 general linear model(GLM) (first–level) analysis. The stimulus was a block designmerged with an event-related design; boxcar functions wereused to define regressors which modelled the onsets and dura-tions of each stimulus, as indicated by each subject by meansof key–presses. Consequently, the regressors were: faces, bod-ies, geometrical state 1 and geometrical state 2. Regressors werefurther subdivided in stables versus unstable; stable onsets corre-sponded to actual changes, while unstable onsets correspondedto perceptual changes, as indicated by key-presses. Key-presseswere modelled as delta functions in an additional regressor.Head-movement parameters calculated from the realignmentpre-processing step and physiological data acquired during thescan (heart-rate and respiration) were included as regressors ofno interest. Regressors were convolved with the default SPM8


canonical hemodynamic response function (HRF), its temporalderivative (TD) and dispersion derivatives (DD). The resultantparameter estimates for each regressor (at each voxel) were com-pared using t–tests to establish the significance of differences inactivation between conditions. We have investigated five maineffects: Unstable Figures vs Stable Figures; in respect to inter–categorical stimuli, Unstable Faces vs baseline and UnstableBodies vs. Baseline; in respect to inter-categorical stimuli, Geo-metrical State 1 vs. Baseline and Geometrical State 2 vs Baseline.Contrast images for these effects for each subject were enteredinto random–effect analyses at the second level. Conjunction

analysisA conjunction analysis [Friston et al., 1999] was performedto asses how the two types of bistable images, intra-categoricaland inter-categorical, each contributed to the areas of activationfound when contrasting all bistable with all stabilised figures.Separate contrasts were made for each for both types of fig-ures: Bistable intra-categorical vs. Stable intra-categorical, andBistable inter-categorical vs. Stable inter-categorical. To make theconjunctions, the contrast Bistable Figures vs. Stable Figures waspaired separately with the contrasts Bistable intra-categorical vs.Stable intra-categorical, and Bistable inter-categorical vs. Stableinter-categorical. Event-related

analysisFor the even-related part of the analysis we made contrasts forinter-categorical stimuli: Bistable Faces vs. All and Bistable Bod-ies vs. All, and in respect to inter-categorical stimuli: Bistablestate 1 vs. All and Bistable state 2 vs. All. Regressors wereconvolved with the default SPM8 canonical hemodynamic re-sponse function (HRF) and a first-order Taylor approximationin terms of the temporal derivative (TD) was added [Fristonet al., 1998]. Whole brain t-maps for main effects of interest andfor temporal and dispersion derivatives were created for eachsubject. Contrast images for the main HRF and its TD were com-puted separately for each effect investigated. Then, second levelrandom-effects models were created for each contrast, using thet-maps from the first-level fixed effects analysis. The onsets ofinternally and externally driven changes were modelled basedon the recorded key presses and set to a fixed duration of onesecond. Perception of faces and bodies as well as the two statesof the intra-categorical figures were also modelled separatelybased on the recorded key presses. A more complex model foranalysing the event-related results has been chosen; adding theTD to the canonical HRF gave us the possibility to model BOLDsignals with deviations in onsets. The Henson et al. (2002) have


demonstrated that it can be useful to model differential latenciesof the HRF as a to investigate if BOLD signal may occur earlieror later then what the canonical parameter estimates.

2.3 results

2.3.1 Behavioural results

All subjects reported that they were able to see the stimuliduring scanning and alternate their key-presses according to theinstructions. Overall, subjects perceived each type of state for asimilar period of time during presentation of bistable images;bistable faces mean 2.5, ± 2.35 s., bistable bodies mean 2.1,±1.47 s., bistable geometrical 1 mean 2.3, ± 1.64 s., and bistablegeometrical 2 mean 2.51, ± 2.29 s. Subjects indicated perceptdurations ranging from .02 to 15.12 s. The periods betweenflips found here are shorter than what subjects indicated inKleinschmidt et al. (1998) who had inter-reversal times of 9.0±2.6 s and 8.1 ± 1.9 s, but in line with studies of ambiguousmotion where similar durations of alternating percepts wereobserved ([Ilg et al., 2008]).Blocked fMRI

analysis: Neuralspecificity of bistable

images

We compared spontaneous and stimulus-driven perceptualswitches. We first contrasted perception of Bistable Figures withperception of Stable Figures with blocked design analysis. Spon-taneous perceptual changes were correlated with increased ac-tivations in right inferior and superior parietal lobules, and inbilateral inferior frontal, middle frontal, and insular cortex. In-creased activity was also observed in regions of the anteriorcingulate cortex, supplementary motor area, and left primarymotor and somatosensory cortex. Selective activation duringperceptual transitions were also found in the right extrastriatevisual cortex and the cerebellum, putamen and thalamus (seeFigures 2.6 and 2.7).Conjunction

analysis: comparinglevels of ambiguity

A conjunction analysis was performed to provide more in-sight into how each type of figures contributed to the overallactivation found during perception of bistable stimuli. Severalsimilar areas of activation were identified for overall bistableperception in conjunction with both inter- and intra-categoricalbistable perceptions respectively (Figures 2.8 and 2.9 ). Therewere clearly also differences between the two conjunctions: theintra-categorical figures evoked bilateral activation of superiorparietal lobule while inter-categorical figures only showed sig-nificant right activation of this region. The significant regions

2.3 results 49

were also noticeably larger for the intra-categorical conjunction,both in frontal and parietal areas. Event-related

results: contrastinginterpretations

We assessed if face perception was correlated with increasedBOLD activation in the FFA, known as a region specificallyinvolved in face processing. We predicted that we would findpercept specific activation during face perception, which hasalso been demonstrated, in previous studies [Andrews et al.,2002]; [Hasson et al., 2001]. As hypothesized, our results showedclear activation in the fusiform gyrus when subjects indicatedperceived faces during inter-categorical stimulus presentation,an activation pattern we did not find in any of the other contrastswith bistable stimuli. To ensure we did not miss any activationfor the contrast Bistable bodies > All, we did a small volumecorrection for the contrast Bistable bodies > All with a 16 mmsphere at [38 -58 -14] which was identified as the extrstriate bodyarea (EBA) [Downing et al., 2001]; no significant voxels wererevealed. For the intra-categorical stimuli we did expect to haveactivations in the same areas for both Bistable state1 > All andBistable state2 > All. Our results showed significant activationonly for Bistable state2 in right middle occipital gyrus. We did asmall volume correction to test if there was possible activationin the same area for State1 with a 16 mm sphere at [36 -85 7].The small volume search revealed a highly significant cluster(x, y, z = 36, -82, 7, Z = 4.79). The central interest of the event-related part of this study was to investigate if activation wouldchange between the two perceptual states for both inter- andintra-categorical bistable images. For the inter-categorical imagesthere was a correlation between face perception and activation inthe fusiform face area, which was not found during perceptionof bodies. For both states of the intra-categorical figures weidentified significant activation in the same area, the middleoccipital gyrus. The middle occipital gyrus has previously beenassociated with spatial attention [Noesselt et al., 2002]. All event-related contrasts showed deactivations in primary visual regionsin line with previous findings by [Kleinschmidt et al., 1998],where deactivations in occipital areas also were found duringbistable perception.

The contrast estimates showed that the main canonical HRFaccounted for very little of the activation (see figure 2.10 for Latencya representative example), while the TD is much larger andpositive which shows that activation actually takes place earlierthan the events [Friston et al., 1998]. For the deactivations in theoccipital regions the TD was negative, indicating that suppres-


sion might take place just before upcoming perceptual switches.Also for the deactivations, the main signal modelled with thecanonical HRF was much lower compared to the estimate of theTD. This could indicate that the deactivations are more transient,and may occur in the transition between perceptual states ratherthan in the period when the percept is temporarily stable.

2.4 discussion

The aim of the first part of our study was to compare spon-Neural specificity ofbistable images taneous perceptual reversals with externally driven changes

in terms of neural activity. In accordance with previous imag-ing studies using bistable percepts [Kleinschmidt et al., 1998];[Lumer et al., 1998], we observed activations in several frontaland parietal areas. As expected we did not find any notableactivations in the primary visual system because the image washeld constant. It is unlikely that our results reflect the motor task,because subjects were doing the same key presses during bothbistable and stabilised stimuli presentation. The frontoparietalactivations could reflect a continuous loop of communicationfrom the visual cortex to higher-order areas. One interpretationis that these areas are involved in a feedback to early visual areas,re-evaluating the multistable percept over: this would supporta top-down explanation. Alternatively, changes are driven bysignals from lower perceptual areas due to destabilization ofthe current percept, in line with the satiation / bottom-up hy-pothesis. The role of the frontoparietal attention network wouldthen be to detect changes or to momentarily stabilise the cur-rent interpretation. The frontal and parietal regions identifiedin our study are similar to the areas found during both volun-tary reversals of bistable images and changes in visual spatialattention [Slotnick et al., 2003]. In the current study, it is notlikely that frontoparietal regions reflect voluntary changes inattention because we specifically instructed the subjects not totry to voluntary elicit the flips, but to signal report reversals.The involvement of these regions in this context suggests a cou-pling between spatial visual attention and dynamic changes ofvisual perception. It is still debatable if these activations reflectinitiation or detection of changes in interpretation. We specu-late that the brain is constantly engaged in interpretation andrevaluation of perceptual input, and during this process atten-tion is shifted to different features of the figure. These changesof attended local features could initiate switches. Our expla-

2.4 discussion 51

nation corresponds to the theoretical framework suggested by[Leopold and Logothetis, 1999], and is supported by behavioralresults showing that attending to different local features of anambiguous figure bias perception [Peterson and Gibson, 1991];[Tsal and Kolbet, 1985]. The pre-central gyrus has found to beinvolved in selective processing of relevant visual targets ratherthan directing attention towards a cued target [Hopfinger et al.,2000]. The area also contains the frontal eye fields, an area alsofound in the study by [Kleinschmidt et al., 1998]. In our studya fixation cross was not used, so activation could be due toreversal-related changes of gaze or covert shifts of attention. Sev-eral areas in the cerebellum were identified when contrastingwhole periods of bistable perception with stabilised replays. Thecerebellum is traditionally associated with movement at speechfunction, but recent studies also show involvement in mentalactivities such as attention, error detection (see [Ito, 2008] for areview). It has also been demonstrated that the posterior partof cerebellum (lobule VII, crus I) supplies temporal informationto frontoparietal spatial attention network involved in visualattention [O’Reilly et al., 2008]. Involvement of the posteriorcerebellum was more active when subjects had to predict thetrajectory of an occluded moving object. In our study, it may bepossible that the cerebellum predicts the upcoming dominantvisual percept.

In the conjunction analysis, larger parts of the overall activa- Levels of ambiguitytions during bistable perception were accounted for by activationduring viewing of intra-categorical figures. There may be severalways to interpret this finding. Our initial hypothesis, in line with[Zeki, 2004], was that reversing figures represent a very simpleform of ambiguity and are not affected by top-down factors,while face/body figures should trigger an activation in frontalareas (top-down). Zeki’s hypothesis seems to contrast the factthat we found larger areas of frontal and parietal activationduring perception of intra-categorical figures. However, theremay also be other explanations.

If, indeed, we are less able to control alternations of intra-categorical figures, and the frontoparietal network reflects de-tection of changes in perception, then increased activity couldbe due to less anticipation of changes. In our study, severalsubjects spontaneously reported that they were able to see bothfigures at the same time for the inter-categorical figures, whilethis was not the case for the intra-categorical ones. This impliesthat inter-categorical are not "purely" bistable, then they are


less effective as stimuli and that could also account for whywe found less ambiguity-specific activation. In order to checkthis hypothesis, after the experiment we asked subjects whetherthey had the impression they could see both images at the sametime in geometrical stimuli and in face/body stimuli. while only12% of the subjects said they could perceive geometrical (intra-categorical) two interpretations at the same time, 56 % said theyhad the impression they could see both face and body in theintra-categorical images. Therefore in terms of ambiguities level,we affirm that intra-categorical images belong to second levelambiguity. For the event-related analysis we hypothesized thatContrasting

interpretations activation would take place within the same brain area for bothstates of the intra-categorical stimuli, while activation wouldchange back and forth between two areas during perceptionof inter-categorical stimuli. As expected, we did find increasedactivation in the same area for both states of the intra-categoricalstimuli. For the inter-categorical stimuli, we did find activationin FFA during face perception in line with previous studies[Andrews et al., 2002]; [Hasson et al., 2001]; [Tong et al., 1998].This supports the general idea that the conscious experience of afigure is correlated with activation in its processing specific area.A cube will remain a cube even if it is seen from a different per-spective, and therefore processing takes place within the samearea. Activation for one state was only found using a small vol-ume correction. A weakness of this study is that it was difficultfor subjects to report which was the dominant interpretation ofintra-categorical stimuli, while it was much easier to assign onebutton to perception of faces and one to perception of bodiesfor the inter-categorical figures. In further studies, our findingscould be supplemented with a similar experiment using am-biguous motion in the future because direction of movement iseasier to report than perspective. The TD of the HRF modellingperception of faces indicates that activation in FFA actually occurbefore the reversal is consciously perceived. This finding is inline with the study by [Andrews et al., 2002] showing that FFAactivation can be detected before subjects report seeing a facewhen looking at the Rubin figure. Also transient deactivationswere found in occipital areas, most consistently in the lingualgyrus. This area has been shown to be sensitive to direction ofspatial attention [Giesbrecht et al., 2003], and similar patterns ofdeactivation have been found during inhibition of unattendedvisual stimuli [Hopfinger et al., 2000]; [Slotnick et al., 2003].

2.4 discussion 53

2.4.1 Conclusion

We addressed the general question of ambiguous perceptionin three different ways. We compared endogenous with exoge-nous changes by contrasting perception of bistable figures witha replay condition using stable figures. With our results, wesupport the hypothesis that frontoparietal processes constantlyre-evaluate the current interpretation of the sensory stimulusinput causing changes in subjective perception. The neural pro-cesses underlying spatial attention and perception of ambiguousstimuli appear to be similar, but the exact role of attention needsto be further investigated. In general, endogenously driven per-ceptual changes seem to involve widely distributed brain areas.Further, we investigated neural correlates of different levelsof ambiguity. Surprisingly, intra-categorical stimuli evoked alarger magnitude frontal and parietal activation than the inter-categorical figures. The implication of this finding is that itmay be useful to distinguish between different types and levelsof ambiguity. We propose that in first level ambiguity fronto-parietal activations are more significant and this fact correlateswith a subjective experience of a more "pure" perception ofbistability, implying the mutual exclusiveness of the stimulusinterpretation. Second level ambiguity, when activations takeplace in two or more different brain areas, may correlate withthe coexistence of interpretations and with a diminished ac-tivity in the fronto-parietal network, which appears to be anambiguity-specific neural activity. Our findings could furtherbe expanded to involve cognitive multistability, such as moreopen-ended ambiguities, referring to gender or racial ambigui-ties [Chiu et al., 2011], situation-related ambiguity [Zeki, 2004]or, as we are going to discuss in the next chapter, the illusionof life. We also found support for the hypothesis that for firstlevel ambiguity, activation takes places within one brain area.During perception of ambiguous figures changing between dif-ferent categories, neural activity fluctuates between two or moreprocessing areas. Our study confirms that activation changes inprocessing areas are correlated with the each stable experiencedpercept over time.


Figure 2.4: Experiment stimuli: bistable intra-categorical images + sta-bilized versions

2.4 discussion 55

Figure 2.5: Experiment stimuli: bistable inter-categorical images + sta-bilized versions


Figure 2.6: Bistable Figures > Stable Figures

2.4 discussion 57

Figure 2.7: Global 3D view of activations for the contrast internalchange > external change for a random effects analysiswith 16 subjects: selected activations superimposed on toaveraged anatomical sections

Figure 2.8: T statistic for Bistable > Stable in conjunction with Intra-categorical: Bistable > Stable switches (left) and Inter-categorical: Bistable > Stable switches (right)


Figure 2.9: Bistable activations conjoined with Inter-categorical andintra-categorical bistable activations

2.4 discussion 59

Figure 2.10: Bistable faces > All. FFA activation projected onto aver-aged structural scans (left) and main HRF and TD plottedfor FFA [38 -58 -14] (right)

Part III

T H I R D L E V E L A M B I G U I T Y

3T H I R D L E V E L A M B I G U I T Y: T H E I L L U S I O N O FL I F E

Chapter II has illustrated how and where in the brain the illu-sion of ambiguity takes place. Introducing the concept of levelsof ambiguity correlating with fronto-parietal activations andcoexistence, at the conscious level, of different possible interpre-tations. In this chapter I propose the concept of life perceptionas an illusion, the illusion of life. This specific illusion resultsin the qualia of attributing aliveness, and animacy attributessuch as intentions and emotions to objects, in spite of the certainknowledge that such objects are not alive. This illusion coulddescend by the specific knowledge of behaviour and appearanceof alive entities; but it is so strong an so compelling that suggeststhat animacy perception is due to a perceptual knowledge, or aninherited concept, that is present in our mind and organises ourperceptions even when we face blatantly non-animated stimuli,like geometrical figures. This illusion may represent a higher(third) level of ambiguity, in line with our results of ChapterII. Such results demonstrate that ambiguity-related activationsare more likely to correlate with intra-categorical images, thatare also the most decidedly "mutually exclusive" interpretations.Inter-categorical images are more likely to be less exclusive. Asthe illusion of life represents a higher level ambiguity, the ob-server will attribute aliveness-related features to objects whilecontinuously maintaining the awareness of their non-aliveness.The illusion of life is so strong and compelling that many studies Automaticity of

illusionsreported the impossibility of preventing the subjects of anthro-pomorphizing stimuli [Schultz et al., 2004]. [Castelli et al., 2000]pointed out that several subjects were anthropomorphising alsorandom-moving stimuli.

3.1 perceptual knowledge of life

Attributes and features of animacy can elicit in us strong au-tomatic reactions that may be classed under that label of "per-ceptual knowledge" which persists in qualia and can contradictconceptual knowledge in illusions. The ability of perceivinganimacy, being obviously useful and especially robust, allows

63

64 third level ambiguity: the illusion of life

us not only to immediately spot all "living beings" surroundingus, but also to attribute intentions, emotions, thoughts, and atheory of mind to them. The mechanism of "life perception"is so powerful that it invariably leads us to assess some "falsepositives", hence the illusion of life: to perceive inanimate objectsas animate, to ascribe them life-related attributes (e.g. intentions,awareness, perceptions), and to experience towards them feel-ings such as empathy and affection. The false positives causedby the efficiency of "life perceptions mechanisms" are always ex-perienced as ambiguous, since they conflate cognitive awarenessof "non-aliveness" with partial perception (qualia) of "aliveness"(e.g. attribution of personality, feeling of sympathy). The natureof the life perception as a crucial specific knowledge causes itsmanifestation as illusion of life in ambiguity-generating situa-tions.The importance of

life perception The evolutionary necessity of spotting alive creatures is mir-rored in our perceptual ability to identify biological movements,which is amazingly effective. This was first demonstrated inclassical experiments by [Johansson, 1973], who showed that afew dots of light placed strategically on a moving human oranimal body are instantaneously organized into the coherentpercept of a living creature.

[Baron-Cohen, 1995] defines a partial aspect of life perceptionas the ID: the Intentionality Detector. ID is a "perceptual devicethat interprets motion stimuli in terms of the primitive volitionalmental states of goal and desire", thus attributing intentional-ity to anything with (apparently) self-propelled motion. ID issupposed to be a very basic function, working through sensorymodalities. It is based on [Premack, 1990] argument that infantsdistinguish between two kinds of objects, those that are andthose that are not self-propelled. Premack follows research linesby [Leslie and Keeble, 1987] that describe the "appropriate stim-ulation" (the percept needed to elicit the concept of causality)as temporal and spatial contiguity between appropriate events.Applying and extending this argument, Premack affirms thatthe brain deduces basic assumptions from motion features, in-ferring the principles of causality, intention and reciprocation.Premack follows the hypothesis that the perception of intentionand causality are "hard-wired perception based not on repeatedexperience but on appropriate stimulation". It is not motionitself that is critical but change: a switch from rest to motion(or vice versa), and from one speed/direction to another; "justas causality is the infant’s principal hard-wired perception for

3.1 perceptual knowledge of life 65

non self-propelled objects, so intention is its principal hard-wired perception for self-propelled objects". [Mandler, 1992]also attempts to investigate what distinguishes the "animate"from the "inanimate", arguing that this is one of earliest con-cepts formed in early development stage, and attributing itsperceptual "gateway" to the analysis of different kinds of motion.Causal perception through motion is a perceptual mechanismfirst studied by [Michotte, 1946]. Causal perception is what al-lows us to "attribute" cause-and-effect relations to facts; thisconcept is so strong that we attribute causality and intentionseven to bi-dimensional moving shapes moving schematically, bydescribing their motions with intentionality verbs. All these re-sults demonstrate that hard-wired brain functions related to "lifeperception" would lead to "false positives" provoking attributionof intentions and goals to inanimate objects or even shapes. Theclassical demonstration of this mechanism is a study by [Heiderand Simmel, 1944], where subjects were asked to describe a filmin which geometric shapes moved. The subjects tended to as-cribe intentionality and causality to the shapes themselves or toconstruct narratives where squares and triangles act as humancharacters. From the neurobiological point of view, Warrington Animacy perception

as a categoryand Shallice [Warrington and Shallice, 1984] led a seminal studyon four patients struck by herpes simplex encephalitis. In all pa-tients, researchers identified a specific difficulty in identifying -visually and verbally - living things more than inanimate objects.This kind impairment has been defined as "category-specificsemantic deficit". Since then, many studies have been carriedout on patients investigating the animate / inanimate categoriesas issues concerning the organisation of conceptual knowledgein the brain. For a complete review of the approaches to thisdebate, see [Caramazza and Mahon, 2006] where it is suggestedthat the domains in which conceptual knowledge regardingthis issue are organised are living animate, living inanimate,conspecifics and tools. Inside each of these domains, the authorssuggest that there would be different mechanisms for the analy-sis of visual form, visual motion, and conceptual knowledge, aswell the attribution of intentional content. From the biologicalperspective, a "perceptual life detector" has been proposed inrelation with biological motion perception in animals [Johnson,2006]. Experiments with scrambled point light displays gaveresults that the researchers interpreted as evidence of a visualfilter "tuned" to motion of the limbs of an animal in locomotion,


thus functioning as a general detection system for articulatedterrestrial animals.

3.2 the illusion of intentionality

As discovered by Johansson, biological motion perception isexceptionally robust in humans (and animals); but, a featureallowing of the illusion of life is that some movements are per-ceived as animate even if what is moving is a blob, dots orgeometrical objects. Motion perception is central to life percep-tion; indeed, motion-related information can not only providethe observers with the feeling of animacy but also cause attri-bution of roles, goals, intention, personality and emotions. Asa common characteristic of illusion, (see Chapter I, about thehollow face perception), also the illusion of life triggered by mo-tion information is perfectly compatible with the awareness ofits deceptive nature. When viewers make "inferences" ascribinganimacy to moving geometric shape, they do it being fully awarethat what they are seeing are geometric shapes. Nevertheless,the illusion is so compelling that it is impossible not to ascribeanimacy to these shapes. Such an automaticity, once again, typ-ical of illusions, is a finding that may be interpreted against apure top-down framework of analysis. Activations correlatingIntentionality in the

social brain with animacy attribution of non-alive stimuli are surprisinglycoincident with neural activations relative to perception of otherindividuals: the temporal parietal junction (TPJ), the FFA andboth ventral and dorsal medial prefrontal cortex (VMPC andDMPC). This areas constitutes what is known as the "socialbrain" [Brothers, 1990], [Skuse et al., 2003]; [Adolphs, 2003] be-cause it is generally activated during social tasks. [Michotte,1946] and [Heider and Simmel, 1944] where the first to investi-Seminal studies on

the illusion of life gate how do motion features could lead to animacy attribution,working in the same years but separately. Michotte with his ex-periment demonstrated that different features of motion can beinterpreted as physically caused while other as psychologicallycaused. For instance, if the surface of moving objects A comesto contact with the surface of object B, and B immediately startsmoving, the event is interpreted by all the viewers as a transferof physical motion. But if B moves not immediately but after apause, the attribution of animacy becomes compelling and themotion is interpreted as psychologically-caused: object B movesbecause object A told it to move or it tries to escape from A etc.Heider and Simmel (1946) have been working on a 2.5 minutes

3.2 the illusion of intentionality 67

movie. The video casts three geometrical shapes, two triangles(a small one and a big one) and a circle. The three shapes weremoving around, in and out a rectangular perimeter, displayingdifferent motion features. During the experiment, subjects wererequested to describe what happened in the video; with veryfew exceptions, the subjects were reporting a narrative includ-ing attribution of intentions, goals, social relations, gender. Forexample, the circle is almost always interpreted as an aggressiveman and the two triangles as a couple trying to avoid him orescape him, while the perimeter is interpreted as a building.Other studies [for a review see (Scholl and Tremoulet, 2000)]have been following this first experiments, trying to identifymotion features of the Michotte tradition and theory of mindissues for Heider and Simmel. In the Michotte tradition, studieson a single moving object have singled out some features linkingmotion to animacy attribution demonstrated that self-propelledmotion is crucial [Stewart, 1982]; [Tremoulet and Feldman, 2000];also, environmental features are important, since animacy canbe seen as emerging from an interaction with the context, as wellas changes in velocity and directions. Studies containing two ormore moving object seems to be more compelling in eliciting theillusion of life, probably because objects constitute environmentand create interaction for each others. [Bassili, 1976] demon-strated that timing is crucial for perception of animacy, sincetemporal events suggest whether the objects are interacting (andtherefore animated) or not; and time contingencies would in-fluence the psychological interpretation. When motion pathsand timing coincided with each other an object was interpretedas "leader" and another one as the "follower", and especiallythe following object was eliciting intentionality attribution, butwhen motion paths were random, the impression of agency waslessened [Dittrich and Lea, 1994] Nevertheless, intentionalitydoes not correspond to animacy, which is a propriety on its own,but contributes to create the illusion of animacy. This is demon-strated by an experiment by [Opfer, 2002] which designed twosets of blobs, identical in shape - but one was autonomouslymoving whilst the other one was "chasing" objects; the ratesof animacy were higher for the intentionality provided blob.[Blythe et al., 1999] studied the interaction possibilities impliedby two objects moving in pair with each other; objects were sim-ple computer cursors "moved" by participants to the experimentwhose had roles to interpret (chase, court, follow). An algorithmbased on a very few motion parameters could successfully cate-


gorise the trials, suggesting that not only intentionality but alsopsychological content can be delivered with very few motionclues. Affective content can be delivered also by motion clues,as demonstrated by [Rime et al., 1985] who found a very highconsensus between US and European subjects while defining theemotions conveyed by geometrical shapes such as the ones usedby Michotte. What is interesting here is that the consensus wasremarkably lower when the shapes were substituted by humansilhouettes. Minimal information seems to be more adequateto elicit the illusion of life, and especially robust in the case ofstimuli like point light displays, and even just limbs [Trosciankoet al., 1996].

Summing up, literature demonstrates that autonomous mo-The role of motiontion, is quite a good way to elicit animacy illusion, but less thengoal directed motion showing an interaction with the environ-ment or between two objects. The illusion of life is so compellingsince based on strong perceptual clues that this mechanismsare valid not only for human adults but also for children andbabies. Infant under 1 year can categorise goal-directed shapes.Furthermore, motion as a clue of intentionality and animacy isstronger when "pure" and not associated with other informationlike form (even if the form openly leads to anthropomorphism).This suggest that intention attribution or agency may be hard-wired in the brain [Scholl and Tremoulet, 2000]; [Tremoulet andFeldman, 2000]. Slightly more complex movement can go furherand convey not only intention but emotions and mental content,as in te study of [Blythe et al., 1999]. Another clue indicating thatform is not useful if not counter-productive is that attributionof intentions and psychological content to Heider-like objects isdue to movements features and changes of location over time,but not to the shapes themselves. Other version of the Heidermovie has been produced, in which movement has been dis-rupted, causing the absence of illusion in the description of thescenes; whilst in a version in which the forms where changedthe description remained the same as with the original movie(Berry et al, 1992).The obligatory

nature of illusions The most striking feature of the illusion of life is its com-pulsory nature, as we said above, typical of illusions. Despiteknowing that we are watching geometrical shapes, the urge toattribute them animacy features is compelling. This "qualia" of"obligatory" perception has been studied by [Hashimoto, 1966]who has been working with a group of observers looking to aHeider-like movie. He told the subjects that they had to describe

3.3 the illusion of life in the brain 69

the shape moving by keeping in mind that they were just look-ing at geometrical objects and thus avoiding any reference toanimacy. The subjects were nevertheless describing the moviewith anthropomorphic terms "leaking" out of the descriptions,and this has been the first demonstration of the obligatory na-ture of the illusion of life. Following Hashimoto’s study, otherresearchers have been investigating such a compelling impres-sion. Other methods used have been counting in the descriptionsthe words depicting social roles, affective content, and a specificanalysis tool - the Linguistic Inquiry and Word Count [Heber-lein, 2008], organising in 74 categories the references to animacyin the description of the stimuli. Using this software, Heberleinand colleagues found that, even explicitly forbidding subjectsto describe in anthropomorphic terms a Heider-like movie, thepercept of intentionality is powerful enough to leak throughthe verbal descriptions: all the subjects failed in describing theshapes without using animacy-related terms. They also foundthat the rate of speech in subjects forbidden to describe themovie in anthropomorphic terms was significantly slower thenthe control group who describing the scene without any instruc-tion; these data demonstrate the effort in overriding the perceptsof intentionality, supporting the hypothesis that intentionalityand animacy are hard-wired being inherited concepts in thebrain.

3.3 the illusion of life in the brain

fMRI studies have been investigating the neural events correlat-ing with the attribution of intentions and perception of animacy.As anticipated at the beginning of the Chapter, many structuresthat appear active when perceiving stimuli eliciting the illusionof life seems to be also involved in perceiving social facts, andindeed the active circuit has been labelled "social brain". Thesebrain areas involve the posterior sperior temporal sulcus (pSTS),the amygdala, the fusiform gyrus, the ventral and medial pre-frontal cortices, the tempo-parietal junction. The social brainalso include this areas, as proposed by [Brothers, 1990] whodefined as a circuit specialised in making inferences about be-haviour (mental states and predictions of actions based on them).fMRI studies have been obtaining such a brain map by scanningsubjects while they were looking or describing Heidder-likeor Michotte-like movies. Generally, this movies were depictingshapes animated by intentions, but animacy, as specified in the


previous section, does not overlap with animacy (but it is avery good cue for it). Animacy correlates have been isolatedwith a contrast analysis from perception of intentions attributionby showing movies of goal directed motions versus physicallyrandom [Schultz et al., 2004], physically but not psychologicallycaused [Blakemore et al., 2003] or geometrical motions [Castelliet al., 2000].Superior temporal

sulcus [Schultz et al., 2005] have been designing an experiment iso-lating perception of movement from animacy perception. Thestimuli used were animations of two autonomously propelleddiscs, in which, periodically, one "chases" or "follows" the otherone. By continuously varying the disc movements, alternatingbetween interactive and non-interactive, the analysis could graspthe perception of interaction isolating it from the perception ofmovement. In the moments in which the movement was interac-tive (when one disc was chasing the other one) the stimuli wereperceived as more animated. When subjects were indeed observ-ing interactive motions, bilateral regions of posterior STS/STGwere found to be activated in contrast with the non-interactive(non correlated) motions. This area was active even when thetask given to subjects was meant to distract their attention fromthe perceived animacy of the objects, for instance, when thesubjects were told to judge velocity or other features irrelevantto animacy. This means that this brain area processes animacyeven in absence of conscious attention devoted to it; neverthe-less, when attention is elicited towards animacy (when subjectsare instructed to observe the interaction between the shapes, orto try to "interpret" the casing strategy of one object) activityin the posterior STS/STG is even increased [Blakemore et al.,2003]; [Schultz et al., 2004]. This suggests that the pSTS/STGis the area specialised for perceiving animacy, as the same areais active is animated in correlation with the event of spottingbiological motion while viewing a point light display stimulus[Zacks et al., 2006].Other activations

Researchers have been trying to identify neural correlates ofanimacy perception. [Castelli et al., 2000] compared activationsof subjects viewing three kinds of Heider-like stimuli: randommovements, goal-directed movements and movements trigger-ing psychological content (e. g. seducing, bullying, etc). Fourregions, pSTS regions, medial prefrontal cortex, fusiform gyrusand extrastriate regions of the lateral occipital cortex were moreactive looking at goal-oriented movements (chasing, following)and in the high-psychological content movements if compared


to random moving stimuli. [Martin and Weisberg, 2003] havefound a consistent map of activations viewing animated actionscompared to objects. In a study showing thre geometrical objectsinteracting, subjects were asked to judge whether the objectswere friends (thus imposing a priori an attribution of animacy)[Schultz et al., 2004] and they showed activations, if comparedto non animated stimuli of which subjects had to evaluate theweight, in the fusiform gyrus, amygdala temporal pole, medialPFC and STS. Particular activations as been found in the FFA, af-ter a localization. This activation of FFA in stimuli without facesmight mean that either the FFA is included in social judgementseven whether stimuli have no faces, or that the FFA might bypotentiated by inputs from the amygdala which as we saw maybe implicated in processing social stimuli. This latter interpreta-tion is reinforced by a damage study [Heberlein and Adolphs,2004] on a subject with a bilateral amygdalal damage, who wasdescribing in totally non-anthropomorphic terms the originalmovie by Heider and Simmel. The role of

amygdala and pSTSThe amygdala is known for processing emotional content,in particular processing fear and rating trustworthiness. Theamygdala may be relevant for directing attention towards so-cially relevant stimuli, since it projects to frontal and temporalregions; thus the amygdala may project signals to pSTS, pre-frontal regions and FFA. pSTS has been considered as relatedto animacy perception and among that area TPJ has been iso-lated among other regions for inference about other’s peoplemind and intentions in contrast with other’s representations[Saxe and Kanwischer, 2003]. Also mPFC has been found tobe active during representations of mind [Amodio and Frith,2006], but bilateral damage does not affect intention attribution[Bird et al., 2004]. Studies did not give any definitive answer,but mPFC seems to be important for processing people-relatedinformation. Top-Down versus

Bottom-up[Wheatley and Martin, 2009] have been addressing the ques-tion whether the illusion of life (which they refer to as anthro-pomorphising) is due to a top-down or bottom-up mechanism.The same set of moving geometrical objects was duplicated andassociated with two different context, one encouraging and theother one discouraging animacy attribution. Brain regions activein the animacy-stabilised versions of the stimuli were once againoverlapping with the social brain: fusifom gyrus, STS, amygdala,insula, mPFC, thus overlapping with the regions active duringattribution of animacy to simple geometrical figures without


biasing for anthropomorphising, and also when subjects wereasked to imagine anthropomorphic attributions. So apparentlytop down information influences the activations of these regions,and not just perceptual information, in a hybrid mechanism asfor first and second level ambiguity.

3.3.1 Emotional clues in the illusion of life

Following neuroscience, then, what are the features allowingthe illusion of life, and thus the activation of the social brain’scircuit? Goal-directedness alone is not enough, as suggested by[Blakemore et al., 2003] and [Schultz et al., 2004] and [Schultzet al., 2005]. Contextual clues also are not crucial, since a verysimple and contextual-free stimulus as the Heider and Simmelmovie is undoubtedly apt to trigger the illusion. On the con-trary, the original movie features several interactions betweenthe shapes (fighting with, escaping and hiding from, protectingand chasing each other). The fact that a bilateral brain damageBrain damage

preventing theillusion of life

at the amygdala prevents from anthropomorphizing the Heiderand Simmel movie [Heberlein and Adolphs, 2004] is an impor-tant clue of what can triggers anthropomorphism. The Heiderand Simmel movie contains emotionally-charged interactions,since it is interpreted as a story of bullying or threatening. It isvery interesting to observe that the emotions observed in themovie are negatives ones. In the movie, the two triangles arebullied, or persecuted, or chased, by the bigger shape; thereis an "happy end", since they gently touch each other in a be-haviour described as "kissing", "celebrating", "high-fiving" bythe subjects. But, this last "event" is seldom included in thedescription of the movie, while the most negative events arealways explicitly described, as the "destruction of the house" (therectangle). Negative events, and thus negative emotions, seemsNegative biasto be more important and drive more attention, and they arethe one which trigger the social interpretation of the stimulus,thus the illusion of life. In this sense, the amygdala damagepreventing anthropomorphism is very meaningful since as spec-ified above the amygdala processes emotional information andespecially fear and threat-related clues. The negative bias in theillusion of life has been suggested also by [Morewedge, 2009]who showed that a negative intention or outcome is more easilyinterpreted as human. During an ultimatum game, subjects wereasked to judge wheter on the "other side" there was a humanor a computer. If confronted with negative behaviours, such a


selfish ultimatum, the subjects would generally rate the agentas human, while if confronted with a generous offer, the agentwould have been rated as a computer. Negativity bias seems tobe linked with the evolutionary necessity of dealing with unpre-dictable and potentially harmful living entities, other humans oranimals; thus, we appear to be more inclined to attribute socialattribution to negative events. It is a necessity which gives riseto false-positives, that from an evolutionist point of view areless harmful than negatives.

Part IV

F O RT H L E V E L A M B I G U I T Y

4A E S T H E T I C S O F A N T H R O P O M O R P H I S M

4.0.2 Anthropomorphism as a forth level ambiguity

The illusion of life is probably the perceptual basis of thosecommon and inescapable phenomena of anthropomorphism,that all of us experienced. Our capacity to invent living agentsand superimpose this belief on objects that are clearly non an-imated is impressive: we name our cars, curse computers andlove gadgets. I consider the illusion of life as the perceptualknowledge leading to inference of aliveness. In this Chapterthis psychological phenomenon is declined in life evocation inthe arts and anthropomorphism in human-machine interaction.Anthropomorphism includes the illusion of life, since it repre-sents a process of inference allowing people imbue the real orimagined behaviour of other agents with human-like charac-teristics, motivations, intentions, or underlying mental states[Epley et al., 2007]. While the illusion of life is universally per-ceived, with the only exception of brain damaged patients, lifeevocation and anthropomorphism are variable depending onbias. Indeed, some agents are more easily anthropomorphisedthan others, some cultures are more likely to anthropomorphisethan others [Asquith, 1986], children anthropomorphise morethan adults [Carey, 1985] and some situations and needs lead toanthropomorphisation [Epley et al., 2008]. On the basis of suchan individual variability, anthropomorphism can be defined asa forth level ambiguity, being a conflation of the awareness ofnon-animacy and qualia of animacy, but which is not alwaysand automatically perceived, as in the case of the illusions weexplored in the previous chapters.

4.0.3 Variability in anthropomorphisation

Research has outlined that different people react in a differentway to anthropomorphisation; research has just begun to explainand predict the variability of this phenomenon [Waytz et al.,2010a]. [Epley et al., 2007] identified three primary determinantsexplaining anthropomorphism. The first is motivation for socialconnection (in a situation of loneliness); experimentally induced

77

78 aesthetics of anthropomorphism

isolation increased tendency to anthropomoprhisation [Epleyet al., 2008]. The second is the need to master our environment.Anthropomorphising a stimulus makes it seem more predictableThe need for

anthropomorphism and understandable, demonstrating that anthropomorphism isincreased by effectance motivation. Effectance is the possibilityto attribute predictability to "behaving" things allow us to havethe impression to understand them easily, and to familiarise,having thus the perception of increased mastery, with the finalgoal of making sense of an otherwise uncertain environment.Research on experimental psychology has demonstrated thatthe experience of unpredictability stimulates attempts to gainmastery [Berlyne, 1962]; [Whitson, 2008]. A study by [Waytzet al., 2010b] demonstrated that unpredictable and unexpectedbehaviour triggers the motivation to understand and explain it.

Life evocation has long been exploited by artists, and anthro-pomorphism has a great potential of application in today’s soci-Ambiguity and artety, where we interact more and more with technological objectssuch as robots and avatars, implicitly designed for embodyingbelievable creatures. Identifying features of believability, anddrawing examples and inspiration from arts and technologycould lead to insights useful both in terms of design and in cog-nitive studies. Yantis identified an analogy between ambiguityand artistic phenomena [Yevin, 2000] proposing a modelisationof perceptual ambiguity (proposing the model of saturation ofattention). Ambiguities have been exploited in artworks suchas paintings by Dali. The most famous example of artistic am-biguity is the Mona Lisa, in the words of Gombrich: "Even inphotographs of the picture we experience this strange effect, butin front of the original in the Paris Louvre it is almost uncanny.Sometimes she seems to mock at us, and then again we seem tocatch something like sadness in her smile" [Gombrich, 1995]. Inthe same perspective, Zeki makes reference to Vermeer’s paint-ing as featuring a higher level ambiguity [Zeki, 2004], whereambiguity displayed here refers to ambiguity of different situa-tions, that can can be interpreted in many different ways.

4.1 life evocation in the arts

4.1.1 Defining life away

The attribution of intention to shapes, motion features and emo-tional clues are all involved in the illusion of life. But, what is"life"? Even if the answer seems to be intuitive and straightfor-

4.1 life evocation in the arts 79

ward, researchers propose that we lack of an adequate theoreticalframework [Cleland and Chyba, 2002]. As Cleland and Chyba What is life?argument, the possibility of define life is now facing the samedifficulties hindering the definition of "water" before the inven-tion of molecular theory, since we still lack a "theory of biologythat allows us to attain a deep understanding of the nature of lifeand formulate a precise theoretical identity for life comparableto the statement water is H20. The distinction between life andnon-life has also been a central issue discussed by Artificial Liferesearcher. The so-called "strong thesis of Artificial Life" has alsoargued that it would be possible to create "life" in some othermedium, abstracting the essence of life from the details of itsimplementation in any particular model, trying to build modelsthat are so life-like that they cease to become models of life andbecome examples of life themselves. Yet, despite the difficultiesin agreeing upon a scientific definition of life, everybody knowswhat "being alive" means in the "ordinary sense"; the difficultieslie in "defining it away", to say reducing it to its "independentlyintelligible properties". Even if there is no consensus about howto "define life away", our perception of something as alive can beelicited by pressing some Darwinian button able to evoke in usa visceral reaction. Life evocation arises when we are confrontedwith perceptions that we know are deceptive, but we feel as trueand real.

4.1.2 Art and the illusion of life

One of the main objectives of art has always been to representand evoke life. Many myths illustrate this idea, beginning fromthe one about the origin of the first painting, as narrated byPliny: the first painting was actually a silhouette draw at can-dlelight by a "Corinthian Maid". She traced the features of her Art imitating lifesleeping lover onto a wall. He was about to leave for a far awaycountry, and she traced this image in order to keep his presencewith her. Another meaningful story is the one of Giotto. Vasarirecounts that when Giotto was only a boy in the studio of hismaster Cimabue, "he once painted a fly on the nose of a facethat Cimabue had drawn, so naturally that the master, returningto his work, tried more than once to drive it away with his hand,thinking it was real"[De Vere, 1912-1915]. Realism and accuracywere intended as the tool for not only representing life, but toattribute to the work of art the ideal feature of communicatingthe feeling of life-like presence, or life evocation. Several other


stories establish a relation between the realism of life represen-tation creating the "illusion" of life with aesthetic appreciationand artistic value. In literature, many histories portraying artistsand focusing on creativity and inspiration stage the ambiguitybetween the inanimate and the animate. Typically, the topoi ofart-related literature include works of art awakening to life, thewill of creating life by means of art, the uncertain nature of acharacter (animate or inanimate, statue or human being). Themost celebrated example of the first category is the Portrait ofDorian Gray, in which the inanimate object (the portrait) absorbssome specific characteristic of its animate counterpart (Dorian),to say moral traits, embodying them through formal features.The second category probably stages a common metaphor forartistic inspiration and creation, ranging from the carpenter whocarved Pinocchio to Pygmalion giving life to his loved statue.The third case, more specifically focused on ambiguity, is thenarrative expedient often used for arousing the feeling of un-canniness, thus used in fantastic and horror fiction, leaving thereader or the main character in uncertainty as to whether awork of art is animate or not. Examples of this mechanism areColomba by Merimée (1840), or A Mystery of the Campagna,(1887) by Crawford, or the most famous Sandman (1816) by ETAHoffman.

Another art exposing the ambiguity of life evocation is pup-petry, a literal enactment of the "animate versus inanimate"contradiction. The main characteristic of puppetry is the "in-escapable tension" that Steve Tillis identifies as being betweenthe material object itself and the object as "signifier of life" [Tillis,1996], setting up a conflict between the puppet as object andthe puppet as life. Indeed, a marionette elicits a double pointof view on the spectator: it is an object but one onto whichthe viewer projects her own emotions and a theory of mind.When attending a puppet show, the spectator is drawn, littleby little, towards increasing her suspension of disbelief, finallygranting the puppet the status of an actor. Puppetry imagery incontemporary art takes, as historic point of departure, AlfredJarry’s 1896 puppet play Ubu Roi. Later, other puppets were fea-tured in works from international well-established artists (suchas Kiki Smith, Pierre Huyghe, Christian Jankowski, Kara Walker,Laurie Simmons). [Cohen, 2006] identifies a first wave of pup-pet imagery appearing in avant-garde art coinciding with theWestern appropriation of masks and other artefacts from exoticculture and folk art. He specifically refers to the Bauhaus and


Futurist artists Jan Toorop and Paul Klee who created abstractpuppet spectacles using geometric figures. In this period Picasso,Cocteau, and Calder created mobile sculptures and puppets; andJoan Miro designed an experimental puppet show, Death to theBogeyman (Mori el Merma, 1978), with monstrous painted bodypuppets drawn from Ubu Roi. From where does this artisticinterest in puppetry stem? Puppets challenge the audience’s un-derstanding of object and life, and question a complex relationwith acting, non-living beings. After the advent of photography,representation has not being anymore the central objective ofart practices. Assuming an auto-reflexive attitude, art has beenexploring other domains, inventing a newer aesthetics includingthe spectator, aware of him-or-herself existing in the same spaceas the work, and being aware of the perceptual relationships thatare established. Cultural trends began to steer art theory andpractice towards concepts of interaction and perception at theend of the 50’s. In 1957 Marcel Duchamp delivered a key lecture,The Creative Act, in which he argued that "the work of art is notperformed by the artist alone", since "ce sont les regardeurs quifont les tableaux" [Sanouillet, 1973]. It was the dismissal of theModernist conception of the art object’s internal self-sufficiencyin favour of a sense of its dependence on contingent, externalfactors such as context and audience participation. How couldartists translate the traditional objective of live evocation in thisnew challenging and changing phase of art development? Manycritics rejected the idea that art should mimic life, and manyartistic trends dismissed this ambition, exploring other visuallanguages, such as abstraction. Especially in modernist aesthet-ics, the repudiation of anthropomorphism was radical. It was infavour of medium specificity, autonomy of the artwork from itsenvironment, and rejected narrative. Nevertheless, life evocationis such a powerful tool - both in terms of human perceptionand artistic expression - that, even if abandoned in theory, itreemerged very soon in practice.

Art evocation re-emerged in contemporary art practices af-ter Modernism, beginning with Minimalism and continuingwith technological and in particular robotic art. These artisticexplorations continued the trajectory of anthropomorphism inWestern art, but switching their focus from representation offormal features to simulation of behaviour as a form of life evo-cation in parallel with a greater attention to elicited perceptualprocesses. Minimalists have delivered anthropomorphic and The return of

anthropomorphismin modern art

mimetic content in their works, not by means of representing


life in a human form, but rather by simulating the feeling ofpresence and interaction. This peculiarity of minimalism hasbeen paradoxically pointed out by a modernist critic, M. Fried,who analysed minimalist works specifically attacking their ten-dency of being "a kind of statue; a surrogate person". The basicswitch of sensibility identified by Fried lays on the fact thatminimalist art produces "objects in situation" which "[occupy] aposition in the world" [Fried, 1967]. These works interlace rela-tions with the spectators, losing the frame and separation fromthe surrounding world (as modernist aesthetics would), embrac-ing objecthood and acknowledging audience, being concernedwith "the actual circumstances in which the beholder encountersthe work" and, eventually, concealing at the core of its theoryand practice "hidden naturalism, indeed anthropomorphism".Robert Morris, a minimalist artist, confirms these features (ofcourse from a positive perspective) in "Notes on Sculpture" [Mor-ris, 1969-1969], in which he argues that the art objects shouldbe designed for triggering physical participation by the visi-tor. In this way, the spectator is directly led towards her ownperceptual activity which is, by the same token, revealed anddisclosed. The "economy of tools" (to which is due the label"minimalism") is precisely intended to reveal the artwork asa relational system by means of a reductionist approach: thework is conceived starting from elementary parameters (light,shape, colour, size) susceptible to entertain continuous changingrelations with the spectator, whose "task" is the physical explo-ration of the artwork. In Fried’s words, the work "depends onthe beholder, is incomplete without him, it has been waiting forhim. And once he is in the room the work refuses, obstinately, tolet him alone - which is to say, it refuses to stop confronting him,distancing him, isolating him". This use of intentional verbs isvery interesting: indeed, being confronted with a minimalist ob-ject "is not entirely unlike [being] distanced, or crowded, by thesilent presence of another person". But, how it is possible thatminimalist works - utterly simple, geometric 3D objects, such ascubes or parallelepipeds - would elicit in the spectator such aninescapable life evocation perception? Writings by minimalistartist Tony Smiths may explain this perceptual phenomenon. Inminimalism, an important feature for eliciting the impression ofbeing confronted by "something alive" probably lies in the sizeof the work: "(not too big, or it would become a monument) nortoo small (it would become an object)" as Smiths claims about hissix-foot cube, "Die". Minimalists have also been designing works


that are "unitary and wholistic shapes", having the perceptualproperty of suggesting an inside: two openly anthropomorphicfeatures. These formal characteristics (an appropriate size, aunitary shape) have always being part of Western traditionalsculpture; but only with Minimalism, which reduced life evo-cation to minimal terms expressive tools, could they be singledout as tactics for eliciting the specific ambiguous perception oflive evocation in the brain of the spectator.

4.1.3 From art to technology

Art addresses questions on how we view, perceive and interactwith our surroundings, changing and evolving in a continuousdialogue with the development of culture and technology. Af-ter the advent of photography and thanks to the advances oftechnology in fields such as robotics and computer graphics,one of the objectives of art practices has become not only torepresent life, but also to simulate it by creating artificial crea-tures crossing category boundaries, and questioning from thecognitive point of view which features can evoke in us life per-ception. These artworks suggest that there is no such a thing asa clear and discrete gap in our perception between animate crea-tures and inanimate objects, but rather a continuous category.In their paradoxical status of quasi-living entities, these artificialcreatures are agents of cognitive dissonance, addressing theambiguities of our perceptions and confronting us with stimulithat we know as deceptive or fictional yet accept as "true" or"real", operating a "suspension of disbelief", feeling empathy orattributing them intentions and self-awareness. These works are Life evocation in

behaviourpaving the way to a time where we will have to interact moreand more with artificial creatures, in a technological world inwhich emotion and its affect will have an increasing prominentrole in technological artefacts. In the future we will probably in-teract more and more with objects crossing category boundaries,as the borders between artificial and organic will be less andless clear. Both in terms of theory and practices, interaction be-tween art, science and technology can help stimulate a new wayof feeling and thinking not achievable through purely rationalinquiry. The issue of life evocation in artificial artefacts is crucialto our technology-oriented society. Indeed, studies demonstratethat our relationships with machines are both natural and social,since our brain mechanisms evoke empathy, trust, uncanniness,etc. towards an assembly of circuits or mechanical pieces. A


technological object can suspend our disbelief, just as would aliterary character or a puppet; moreover, we project our feelingsand attachment more and more on virtual worlds, and we be-come operators or "interactors" with many on-line puppets (theavatars) that represent ourselves or others in the digital realm.Robots, like puppets, are an example of the ontological paradoxthat can take place in our technology-saturated environment, asentities simultaneously occluding and exposing their artificiality.

4.1.4 Uncanniness as a result of life evocation

The concept of the "uncanny" can be explored as a first exampleof concept concerning life evocation leaked from aesthetics totechnology. Ambiguity related to life evocation has been sin-gled out and discussed in theory of literature and psychology,where it elicits, following Jentsch (Jentsch 1909) and then Freud(Freud 1919), specific feeling of "uncanniness", which the twoauthors define as the result of the process of familiarity (heim-lich) turned unfamiliar (unheimilich, translated in English as"uncanny"). Among the example proposed by Jentsch and thentaken up by Freud, there are wax figures, which have the "abilityto retain their unpleasantness after the individual has taken adecision as to whether it is animate or not". Jentsch suggests thatthis feeling is caused by "secondary doubts which are repeat-edly and automatically aroused anew when one looks again andperceives finer details; or perhaps it is also a mere matter of thelively recollection of the first awkward impression lingering inone’s mind". Jentsch intuition has been translated into roboticsin the 70’ies with the so-called "Uncanny Valley" [Mori, 1970],The Uncanny Valleypromoted by robotic pioneer Mori and illustrated in Figure 4.1.The Uncanny Valley (a translation from the Japanese "BukimiNo Tani") theory states that as the level of human-likeness in-creases up to a certain point the sense of familiarity with therobot increases as well, but only up to a certain point; beyondthis it drops off suddenly as robots become too human-like andthus appearing uncanny. In his diagram showing this negativepeak, Mori introduces movement as a factor reinforcing the per-ception of uncanniness or familiarity. The first part of Mori’smodel describes the increasing of the sense of familiarity up tothe maximum peak, after which the uncanny valley opens up.From the other side of the valley another positive peak grows incorrespondence with creatures reproducing human attributesexactly and finally with healthy human subjects.

4.2 the illusion of life in artificial creatures: features of believability 85

Figure 4.1: The Uncanny Valley graph following Mori

4.2 the illusion of life in artificial creatures : fea-tures of believability

In the field of Human/Robot Interaction (HRI) and ComputerGraphics (CG), the notion of life evocation is translated into theconcept of believability. Definitions of believability are numerousand diversified: the issues emerging from studies concern tradi- Believabilitytional agents’ properties (agents can be robots or avatars, or anyartificial artefact that acts) concern social functions, behaviour,and a relationship with the environment. At a basic level, believ-ability is a specific property of artificial agents aiming the user’ssuspension of disbelief and "illusion" of life, triggering one’s"instinctive" reaction. Researchers attempting to create engagingartificial creatures both in the HRI and in the CG fields may findimportant insights in the work of artists who have explored lifeevocation. Researchers in artificial intelligence and robotics havebuilt various types of social robots which can express emotions.Research pursues such a goal mainly through speech, facial ex-pressions and hand gestures. Indeed, it is generally a commonhypothesis in research that if robots have salient human-likeattributes, then people’s mental models of robotic assistants willbecome more anthropomorphic as they interact with them. It is


a common hypothesis in the scientific community that in orderto achieve a higher degree of empathy robots should have ahuman-or-pet-like shape, or a very realistic anthropomorphicshape [Kiesler and Goetz, 2002].

4.2.1 Form: is realism a necessity?

While the efforts of robotic design research on emotions is gen-erally focused on developing robots with anthropomorphic fea-tures such as hand and facial expressions [Roccella et al., 2007].A small but still focused part of qualitative research has directlyfaced the question whether anthropomorphic appearance affectsbelievability, generally giving a positive answer, stating that themore the artificial creature is realist and human-like the morecan trigger empathy and emotions. Other researchers tried toget inspiration from the arts, especially in the field of CG, stat-ing "that artists tell us are needed to present the convincing,persistent, illusion of life" [Bates, 1994]. But, artistic practiceswith the goal of believability and arousal of empathy follow theopposite path: in order to create a believable creature, realism isnot a necessity, and for evidence we can look to artists’ creationWhy looking at the

arts? of believable characters. For instance, an analysis of robotic artpractice may suggest that non-humanoid creatures trigger empa-thy and believability as effectively as humanoid ones. Bill Vornis an artist whose work is focused on life evocation. His instal-lations involve robotics, motion control, sound, lighting, video,and cybernetic processes. The aim of his robotic art projects isto induce empathy from the viewers towards characters whichare nothing more than simple articulated metal structures. Thestrength and richness of Vorn’s mechanical machines relies onhuman perception of basic reactive behaviours in robots (es-sentially based on sensors) and by an appropriate immersiveaudiovisual context that sets an environment for the works. But,when confronted with Vorn’s machines (which in terms of shapeare totally non-humanoid), an inevitable reflex of empathic pro-jection arises. In Vorn’s case, the whole realistic appearance isdismissed in favour of a few repetitive movements and simpleinteractions. Artistic creatures are often a distillate of a fewtraits, abstracted from reality, and allowing enough space for thespectator to project feelings and interpretations. Caricaturingis a means for capturing the essence, as in the words of two ofthe most famous Disney animators, Thomas and Johnston, whodescribed their techniques they used in order to create believ-


able characters: "The more an animator goes toward caricaturingthe animal, the more he seems to be capturing the essence ofthat animal. If we had drawn real deer in Bambi there wouldhave been so little acting potential that no one would have be-lieved the deer really existed as characters. But because we drewwhat people imagine a deer looks like, with a personality tomatch, the audience completely real" [Thomas and Johnston,1981, reprint 1997]. Believability does not require human form,as suggested by the arts. Drawing another example from Disneyanimations, we can quote the Fliying Carpet starred in the filmAladdin (1992): it has no eyes, limbs nor even a head. It is only acarpet that can move. And yet, it has a definite personality withits own goals, motivations and emotions, thus is able to evokelife. Unpredictability

"Petit Mal", an artwork by Australian artist Simon Penny, ex-plicitly attempts to explore autonomous behaviour as a probe ofemotion, expression, and believability. "Petit Mal" (an epilepticcondition, a lapse of consciousness), displays an unpredictablebehaviour and is not only an artistic exploration of a medium’spotential but also an act of humour on the typical conventionalidea of control in robotics: the device is "anti-optimized" to in-duce the maximum level of personality. Thanks to its sensors,Penny’s "Petit Mal" senses and explores architectural space, re-acting to people in its environment. Its form and behaviourare neither anthropomorphic nor zoomorphic, but it is clearlyperceived as a living creature by observers interacting with it,since they never gain complete control over the system (as intraditional man/machine interaction). This "reactive" model isa communication scheme which is closer to the relationshipbetween living organisms and their environment if comparedto the common interactive model where the system is waitingfor an input from the user in order to react. In a reactive con-text proper to autonomous systems, the objects react on theirown "will", by themselves, and without the required presence ofviewers, communicating a personality through motion [Penny,1997], and eventually evoking life by other means that form. Thecentral feature of this robot is unpredictability: it never reactsin the same way in the same way to people surrounding it,therefore, is elicits anthropomorphising. [Waytz et al., 2010a]demonstrated that increasing the perceived unpredictability of anon-human agent increases the motivation for mastery and thusanthropomorphism. Anthropomorphising a stimulus makes itseem more predictable and understandable, demonstrating that


anthropomorphism is increased by effectance motivation. Ef-fectance is the possibility to attribute predictability to "behaving"things allow us to have the impression to understand them eas-ily, and to familiarise (giving names to hurricanes) having thusthe perception of increased mastery, with the final goal of mak-ing sense of an otherwise uncertain environment. For example[Berlyne, 1950] identifies uncertainty of the environment the pri-mary motivation for babies to master their environment. Fromthis seminal publication on, research on experimental psychol-ogy has demonstrated that the experience of unpredictabilitystimulates attempts to gain mastery [Berlyne, 1962]; [Whitson,2008]. A study by [Waytz et al., 2010b] carried out a study whereparticipants were confronted with malfunctioning computersand unpredictable gadgets, following surprising patterns of be-haviour. The more frequently computers malfunctioned, or themore the gadget was rated as unpredictable, the higher wasthe anthropomorphisation tendency. For instance, in order totrigger anthropomorphism in the the AIBO (a dog robot) Sonyresearchers have been working on programming this robot inorder to make it preserve its "free-will". Systems of behaviour ofthe AIBO consisted of a base (the "instinct" of the robot"); therobot can learn from the user and be trained, but its instinctswill never be completely cancelled. Also, the AIBO has beenprogrammed with "moods" influencing the reaction in time totraining and to enhance perception of unpredictability [Kaplan,2001].Negative bias

As we saw in Chapter II, negative bias can influence anthro-pomorphism. Anyone had the feeling of attributing a mind toa computer after a crash, with a feeling of frustration; 790/00of people scold and 73 0/00 curse their computer when theydo not "behave" following their intentions [Luczak et al., 2003].Looking back at the arts, it is quite surprising that any robotsdesigned by artists exhibit a negative behaviour, such as suffer-ing. The Suffering Machine by Ricardo Nascimiento, withoutbeing anthropomorphic in shape, is a clear example of howartistic intuition can come to the same results than neuroscience.The Suffering Machine is a robot consisting of three arms orlegs all connected at the same joint. All of the robot’s limbsare controlled by a separate motor, although one of the motorsis purposely weak in an attempt to invoke a type of artificialhandicap. This design poses difficulties for the machine to movearound its immediate environment and thus attempts to pro-voke an emotional connection between the audience and the


object, triggering individuals’ empathy with the difficulties ofmovement of the robot. If someone attempts to reach down tohelp it, the robot plays "dead", thus not accepting any outsideaid. Even an everyday object can trigger empathy, if its move-ments and behaviour are consistently designed: the animatedartwork survivor, designed by artist Laura Morelli, is a roboticchair that walks and react to the surrounding environment, inthe attempt to emulate and suggest some feeling and behavioursthat are typical of survivors of land-mines blasts learning to usecrutches. This has the aim of sensitizing viewers and usuallyprovokes very strong empathy reactions in the public. Animal behaviour

Another common way of evoking life in robotic artworks issimulating specific kinds of animal behaviours such as flocking.Indeed, robotic art has been linked with Artificial Life, thestudy of artificial systems which exhibit behaviour characteristicof natural living systems with a bottom-up approach. This isin contrast with the classical Artificial Intelligence top-downapproach. Some robotic artworks are A-Life sculptures, such asthe works by Yves Klein [Klein, 1998]. The process of creating a"living sculpture" involves developing technologies for gesture,locomotion, sensory input, and behaviour to achieve a unifiedcreature. For instance, Octofungi is an eight-sided polyurethanesculpture that uses a neural network to integrate current eventsvia multiple sensors and shape-metal alloy for silent, non-linearmotion. Motion provided to the robotic creatures is specific tobiological forms, chain reactions, propagation and aggregationbehaviour, herds and swarms. The same interest for biologicallyspecific motion is to be found in Flock by Ken Rinaldo. The Flockconsists of an assemblage of hanging robotic arms that interactwith one another and with viewers, to manifest a "flocking"behaviour that develops from an awareness of each other andthe environment. The artworks’ behaviour is analogous to theflocking found in natural groups such as birds, schooling fish, orflying bats. Flocking behaviours demonstrate characteristics ofsupra-organization, of a series of animals or artificial life formsthat act as one. They are complex interdependent interactionswhich require individual members to be aware of their positionin relation to others.

Another important factor eliciting believability by means ofemotion attribution and empathy can be attributed to infantile-like form. For Konrad Lorenz [Lorenz, 1970] juvenile traits auto- Feeding and

empathymatically trigger a reaction of empathy and tenderness. Featuresidentified by Lorenz are "a relatively large head, a disproportion-


ately large forehead, large eyes placed underneath, prominentcurved cheeks, short thick limbs a firm elasticity, and awkwardmovements". These are the same principles used by CynthiaBreazeal in order to design the robot Kismet [Breazeal, 2000].Kismet is a robotic head which interact with his environment ina non-verbal modality. The robot is very expressive, designedwith big eyes eliciting empathy and encouraging interaction.Kismet can express emotions only by varying the position ofhis head, neck, ears and eyes. Lorenz’s shapes triggering em-pathy are largely independent from realism, as it appears inother robotic creatures designed for interaction, as the AIBO,Furby or Paro. On the contrary, if the above quoted theory of theUncanny Valley is true, a resemblance which is too close withan existing living being may be counter-productive in termsof empathy. Paradoxically in this forth level of ambiguity it isprobably necessary that the creature is perceived as artificial tofully elicit anthropomorphism. Movements, just as in the case ofthe illusion of life, is a crucial feature for eliciting empathy. Con-trary to the Kismet, the AIBO does not have juvenile features inform, but in movement: his movement being awkward, he elicitthe idea of a puppy; when it is switch off, many users can findhim repulsive and cold [Kaplan, 2001].

[Thomas and Johnston, 1981, reprint 1997] refer to personal-ity as the most important requirement for creating believablePersonalitycharacters, defining personality as "all the particular details -especially details of behaviour, thought and emotions - thattogether define the individual. The second requirement for be-lievable agents is that they appear to have emotional reactionsand to show those emotions in some way. This is such a funda-mental requirement in the traditional character-based arts thatoften artists refer to expressing the emotions of their charactersas what brings them to life.

4.3 conclusions

An inspiring function of both art and technology is to go beyondrepresentational "likeness" for evoking the feeling of life itself,triggering those qualia emerging when we are confronted withan animated creature. In two domains as different as these, sucha function has different objectives and strategy of accomplish-ment, but a common perceptual feature: the possibility to conveythe impression that and object is alive despite the exact aware-ness that it is not. It is undoubtedly not too difficult to press our

4.3 conclusions 91

"Darwinian buttons" since, probably for evolutionary reason, weare biased to perceive life: "there is a universal tendency amongmankind to conceive all beings like themselves, and to transferto every object, those qualities, with which they are familiarlyacquainted, and of which they are intimately conscious". It isknown from cognitive sciences that the human brain organisesexternal reality abstracting it, in order to make it meaningful;life, therefore, could be an inborn perceptual category that wespontaneously apply even at the price of cognitive dissonance.Thus life perception could be thought of as an optical illusion,not so different from seeing two lines diverging even knowingthey are parallel, and in general similar to those phenomenacausing a friction between what we know (conceptual knowl-edge) and what we feel (perceptual knowledge): a temporaryoverriding of bottom-up impressions on top-down awareness.In particular, life perception of non-animated objects could beassimilated to the illusion of ambiguity, traditionally definedin literature as the possibility for a stimulus to be stably in-terpreted in only one way at a given moment, but in two ormore different ways over time. In this thesis I investigated, bymeans of an fMRI study, how the illusion of ambiguity relatesto perception of categories, by using stimuli whose interpretablecontent is known form previous studies to be processed in dif-ferent brain areas, namely geometrical figures, faces and bodies.In line with the initial hypothesis, in the case of geometricalambiguous images, for both possible interpretations activationswhere found in the same area, the middle occipital gyrus. In thecase of face-body ambiguous images, there was a correlationbetween face perception as indicated by the subjects and theFFA, known as the area processing faces. Previous studies onthe illusion of ambiguity have consistently shown a networkof frontal-parietal activations in correlation with the percep-tion of ambiguous images when contrasted with their stablecounterparts. In line with literature, the contrast between stableand bistable images revealed increased bilateral activations inthe superior frontal gyrus and in the superior parietal lobule.Surprisingly, the activation of this network was significantlylarger for geometrical ambiguous images (intra-categorical) thenfor face-body ones (inter-categorical), as if the latter were lesseffective stimuli in terms of ambiguity, being not purely bistable.A qualitative questionnaire outlined how 56 % of subjects hadthe impression they could see both images at the same timein the case of inter-categorical images. The implication of this


findings is that it may be useful to distinguish between differentlevels of ambiguity, in which the first one correlates with a more"pure" perception of bistability implying the mutual exclusive-ness of the two possible interpretations. Second level ambiguitymay correlate with the coexistence of the two interpretationsand a diminished activity in the fronto-parietal network. In thisframework, we identified the illusion of life as a third levelambiguity. The illusion of life is the attribution of alivenessfeatures (desires, goals, intentions, strategies) to simple geomet-rical moving figures. In this case, activations are surprisinglycoincident with neural activations relative to perception of otherindividuals, corresponding to those activations constituting the"social brain"; in particular, the posterior and superior temporalsulcus and gyrus activates in correlation with animacy, as theydo in correlation with spotting biological motion while viewinga point-light display stimulus, and the amygdala, known forprocessing emotion-related information. While a frontal braindamage can prevent subjects to see flips of ambiguous images,an amygdala damage can prevent the illusion of life, and mentalattributions are often inappropriate in autistic children. Exceptfor this cases, the illusion of life is universally perceived, whilevariability in what I identified as a forth level ambiguity, an-thropomorphism, is much higher, depending on culture, ageand needs. In this last level of ambiguity I believe that mergingbetween art and technology could be especially fruitful. Indeed,anthropomorphism as life evocation as long been exploited byart, and it has a great potential of application in today’s society,where we interact more and more with artificial creatures suchas robots and avatars. As a future work. it could be interestingto investigate in depth which are the insights that art could sug-gest both to cognitive sciences and technological applications.Artworks suggest that there is no such a thing as a clear anddiscrete gap in our perception between animate creatures andinanimate objects, but rather a continuum. In their paradoxi-cal status of quasi-living entities, these artificial creatures areagents of cognitive dissonance, addressing the ambiguities ofour perceptions and confronting us with stimuli that we knowas deceptive or fictional yet accept as "true" or "real", operatinga suspension of disbelief, feeling empathy or attributing themintentions and self-awareness. These works are paving the wayto a time where we will have to interact more and more with ar-tificial creatures, in a technological world in which emotion andits affect will have an increasing prominent role in technologi-

4.3 conclusions 93

cal artefacts. In the future we will probably interact more andmore with objects crossing category boundaries, as the bordersbetween artificial and organic will be less and less clear. Both interms of theory and practices, interaction between art, scienceand technology can help stimulate a new way of feeling andthinking not achievable through purely rational inquiry.

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