Categories and concepts- introduction CS182/Ling109/CogSci110 Spring 2006

Categories and concepts- introduction

CS182/Ling109/CogSci110

Spring 2006

Lecture Outline

• Categories– Basic Level– Prototype Effects– Neural Evidence for Category Structure

• Aspects of a Neural Theory of concepts• Image Schemas

– Description and types– Behavioral Experiment on Image Schemas

• Event Structure and Motor Schemas

Concepts

• What Concepts Are: Basic Constraints– Concepts are the elements of reason, and – constitute the meanings of words and linguistic

expressions.

Concepts Are:

•Universal: they characterize all particular instances; e.g., the concept of grasping is the same no matter who the agent is or what the patient is or how it is done.

•Stable.

•Internally structured.

•Compositional.

•Inferential. They interact to give rise to inferences.

•Relational. They may be related by hyponymy,

antonymy, etc.

•Meaningful.

•Not tied to the specific word forms used to express

them.

Concepts: Traditional Theory

• The Traditional Theory– Reason and language are what distinguish human

beings from other animals.– Concepts therefore use only human-specific brain

mechanisms.– Reason is separate from perception and action, and

does not make direct use of the sensory-motor system.– Concepts must be “disembodied” in this sense.

The neural theory

Human concepts are embodied. Many concepts make direct use of sensory-motor, emotional, and social cognition capacities of our body-brain system.

• Many of these capacities are also present in non-human primates.

Classical vs prototype model of categorization

• Classical model– Category membership determined on basis of essential

features– Categories have clear boundaries– Category features are binary

• Prototype model– Features that frequently co-occur lead to

establishment of category– Categories are formed through experience with

exemplars

Prototype theory

1. Certain members of a category are prototypical – or instantiate the prototype

2. Categories form around prototypes; new members added on basis of resemblance to prototype

3. No requirement that a property or set of properties be shared by all members

4. Features/attributes generally gradable

5. Category membership a matter of degree

6. Categories do not have clear boundaries

Prototype theory1. Certain members of a category are prototypical – or

instantiate the prototype

Category members are not all equal

a robin is a prototypical bird, but we may not want to say it is the prototype, rather it instantiates (manifests) the prototype or ideal -- it exhibits many of the features that the abstract prototype does

“It is conceivable that the prototype for dog will be unspecified for sex; yet each exemplar is necessarily either male or female.” (Taylor)

3. No requirement that a property or set of properties be shared by all members -- no criterial attributes

– Category where a set of necessary and sufficient attributes can be found is the exception rather than the rule

– Labov household dishes experiment• Necessary that cups be containers, not sufficient since many things

are containers

• Cups can’t be defined by material used, shape, presence of handles or function

Prototype theory

Prototype theory

– Wittgenstein’s examination of game• Generally necessary that all games be amusing, not

sufficient since many things are amusing

• Board games, ball games, card games, etc. have different objectives, call on different skills and motor routines

- categories normally not definable in terms of necessary and sufficient features

• What about mathematical categories like odd or even numbers? Aren’t these sharply defined?

– (Armstrong et al.) Subjects asked to assign numbers a degree of membership to the categories odd number or even number

3 had a high degree of membership, 447 and 91 had a lower degree (all were rated at least ‘moderately good’)

Prototype theory

Categories - who decides?

• Embodied theory of meaning- categories are not pre-formed and waiting for us to behold them. Our need for categories drives what categories we will have

• Basic level categories - not all categories have equal status. The basic level category has demonstrably greater psychological significance.

Basic-level categories

chair desk chair easy chair rocking chair

furniture lamp desk lamp floor lamp

table dining room table coffee table

Superordinate Basic Subordinate

Categories & Prototypes: Overview

• Three ways of examining the categories we form:– relations between categories (e.g. basic-level category)

– internal category structure (e.g. radial category)

– instances of category members (e.g. prototypes)

Furniture

Sofa Desk

leathersofa

fabricsofa

L-shapeddesk

Receptiondisk

Basic-Level Category

Superordinate

Subordinate

Basic-level -- Criteria

• Perception – – overall perceived shape– single mental image– fast identification

Basic-level -- Criteria

• Perception

• Function – motor program for interaction

Basic-level -- Criteria

• Perception

• Function

• Words –– shortest– first learned by children– first to enter lexicon

Basic-level -- Criteria

• Perception

• Function

• Communication

• Knowledge organization –– most attributes are stored at this level

Basic-Level Category

• Perception: – similar overall

perceived shape

– single mental image

– (gestalt perception)

– fast identification

• Function: – general motor program

• Communication: – shortest

– most commonly used

– contextually neutral

– first to be learned by children

– first to enter the lexicon

• Knowledge Organization:– most attributes of category

members stored at this level

What constitutes a basic-level category?

Other Basic-level categories

• Objects

• Colors

• Motor-routines

Concepts are not categorical

Mother

• The birth modelThe person who gives birth is the mother

• The genetic modelThe female who contributes the genetic material is the mother

• The nurturance modelThe female adult who nurtures and raises a child is the mother of the child

• The marital modelThe wife of the father is the mother

• The genealogical modelThe closest female ancestor is the mother

(WFDT Ch.4, p.74, p.83)

Radial Structure of Mother

The radial structure of this category is defined with respect to the different models

CentralCase

Stepmother

Adoptivemother

Birthmother

NaturalmotherFoster

mother

Biologicalmother

Surrogatemother

Unwedmother

Geneticmother

Marriage

• What is a marriage?

• What are the frames (or models) that go into defining a marriage?

• What are prototypes of marriage?

• What metaphors do we use to talk about marriages?

• Why is this a contested concept right now?

Concepts and radial categoriesConcepts can get to be the "prototype" of their category in

various ways. • Central subcategory (others relate to this)

• Amble and swagger relate to WALK• Shove relates to PUSH

• Essential (meets a folk definition: birds have feathers, beaks, lay eggs)

• Move involves change of location.

• Typical case (most are like this: "sparrow")• Going to a conference involves air travel.

• Ideal/anti-ideal case (positive social standard: "parent"); anti-ideal case (negative social standard: "terrorist")

• Stereotype (set of attributes assumed in a culture: "Arab")• Salient exemplar (individual chosen as example)

Category Structure• Classical Category:

– necessary and sufficient conditions

• Radial Category: – a central member branching out to less-central and non-central cases

– degrees of membership, with extendable boundary

• Family Resemblance: – every family member looks like some other family member(s)

– there is no one property common across all members (e.g. polysemy)

• Prototype-Based Category• Essentially-Contested Category (Gallie, 1956) (e.g. democracy)

• Ad-hoc Category (e.g. things you can fit inside a shopping bag)

Prototype• Cognitive reference point

– standards of comparison

• Social stereotypes– snap judgments

– defines cultural expectations

– challengeable

• Typical case prototypes– default expectation

– often used unconsciously in reasoning

• Ideal case / Nightmare case– e.g. ideal vacation

– can be abstract

– may be neither typical nor stereotypical

• Paragons / Anti-paragons– an individual member that

exhibits the ideal

• Salient examples– e.g. 9/11 – terrorism act

• Generators– central member + rules

– e.g. natural number = single-digit numbers + arithmetic

Neural Evidence for category structure

• Are there specific regions in the brain to recognize/reason with specific categories?

Category Naming and Deficits

• People with brain injury have selective deficits in their knowledge of categories.

• Some patients are unable to identify or name man made objects and others may not be able to identify or name natural kinds (like animals)

A PET Study on categories (Nature 1996)

Study

• 16 adults (8M, 8F) participated in a PET (positron emission tomography) study.– Involves injecting subject with a positron emitting radioactive

substance (dye) – Regions with more metabolic activity will absorb more of the

substance and thus emit more positrons– Positron-electron collisions yield gamma rays, which are detected

• Increased rCBF (regional changes in cerebral blood flow) was measured– When subjects viewed line drawings of animals and tools.

The experiment

• Subjects looked at pictures of animals and tools and named them silently.

• They also looked at noise patterns (baseline 1)• And novel nonsense objects (baseline 2)• Each stimulus was presented for 180ms followed

by a fixation cross of 1820 ms.• Drawings were controlled for name frequency and

category typicality

PremotorACC

Left middle temporal gyrus

Calcarine Sulcus

Conclusions

• Both animal and tool naming activate the ventral temporal lobe region.

• Tools differentially activate the ACC, pre-motor and left middle temporal region (known to be related to processing action words).

• Naming animals differentially activated left medial occipital lobe (early visual processing)

• The object categories appear to be in a distributed circuit that involves activating different salient aspects of the category.

Action Words- an fMRI study

• Somatotopic Representation of Action Words in Human Motor and Premotor Cortex– Olaf Hauk, Ingrid Johnsrude,and Friedemann

Pulvermuller*– Medical Research Council, Cognition and Brain

Sciences Unit Cambridge, United Kingdom– Neuron, Vol. 41, 1–20, January 22,

2004, Copyright 2004 by Cell Press

Traditional theory

• Unified meaning center in the left temporal lobe.– Connected to Wernicke’s area– Experiments on highly imageable words/nouns.

• Vocalization and grammar associated with frontal lobe– Connected to Broca’s area

Do action words activate the motor cortex

• Given: Cortical representations of the face, arm, and leg are discrete and somatotopically organized in the motor and premotor cortex

• Hypothesis: Words referring to actions performed with the face, arm, or leg would activate premotor networks.– neurons processing the word form and those processing the

referent action should frequently fire together and thus become more strongly linked, resulting in word-related networks overlapping with motor and premotor cortex in a somatotopic fashion.

• Experiment: An fMRI study with word stimuli from different effectors (face, arm, or leg). ROI based on movements (face, arm, leg)

Somatotopy in STS and MC

The Experiment• In order to find appropriate stimulus words, a rating study was first

performed. – Subjects were asked to rate words according to their action and visual

associations and to make explicit whether the words referred to and reminded them of leg, arm, and face movements that they could perform themselves

• From the rated material, 50 words from each of the three semantic subcategories were selected and presented in a passive reading task to 14 right-handed volunteers, while hemodynamic activity was monitored using event-related fMRI.

• The word groups were matched for important variables, including word length, imageability, and standardized lexical frequency, in order to minimize physical or psycholinguistic differences that could influence the hemodynamic response.

• To identify the motor cortex in each volunteer individually, localizer scans were also performed, during which subjects had to move their left or right foot, left or right index finger, or tongue.

Norming

(B) Mean ratings for the word stimuli obtained from study participants. Subjects were asked to give ratings on a 7 point scale whether thewords reminded them of face, arm, and leg actions. The word groups are clearly dissociated semantically (face-, arm-, and leg-related words).

All Actions

(C) Activation produced by all action words pooled together. Results are rendered on a standard brain surface (left) and on axial slices of the same brain (right).

Correlation with BOLD Signal

Neural Evidence for category structure

• Are there specific regions in the brain to recognize/reason with specific categories?

• No, but there are specific circuits distributed over relevant regions of the brain.

• What might the general characteristics of such circuits look like?

What are schemas?

– Regularities in our perceptual, motor and cognitive systems

– Structure our experiences and interactions with the world.

– May be grounded in a specific cognitive system, but are not situation-specific in their application (can apply to many domains of experience)

Basis of Image schemas

• Perceptual systems

• Motor routines

• Social Cognition

• Image Schema properties depend on– Neural circuits

– Interactions with the world

Image schemas

• Trajector / Landmark (asymmetric)– The bike is near the house – ? The house is near the bike

• Boundary / Bounded Region – a bounded region has a closed boundary

• Topological Relations– Separation, Contact, Overlap, Inclusion, Surround

• Orientation– Vertical (up/down), Horizontal (left/right, front/back)– Absolute (E, S, W, N)

LMTR

bounded region

boundary

Similarity:

• Perceptual and motor systems

• Basic functional interactions with the world

• Environment

Variation:

Cross-linguistic variation in how schemas are used.

Cross-linguistic Variations

English

Japanese

English

ON

AROUND

OVER IN

Bowerman & Pederson

Dutch

Bowerman & Pederson

AAN

OM

BOVEN IN

OP

Chinese

Bowerman & Pederson

SHANG

ZHOU

LI

Spatial schemas

• TR/LM relation

• Boundaries, bounded region

• Topological relations

• Orientational Axes

• Proximal/Distal

Trajector/Landmark Schema

• Roles:Trajector (TR) – object being located

Landmark (LM) – reference object

TR and LM may share a location (at)

TR/LM -- asymmetry

• The cup is on the table

• ?The table is under the cup.

• The skateboard is next to the post.

• ?The post is next to the skateboard.

Boundary Schema

Region ARegion B

Boundary

Roles:BoundaryRegion ARegion B

Bounded Region

Roles:Boundary: closed

Bounded Region

Background region

Topological Relations

• Separation

Topological Relations

• Separation

• Contact

Topological Relations

• Separation

• Contact

• Coincidence:

Topological Relations

• Separation

• Contact

• Coincidence:- Overlap

Topological Relations

• Separation

• Contact

• Coincidence:- Overlap- Inclusion

Topological Relations

• Separation

• Contact

• Coincidence:- Overlap- Inclusion

- Encircle/surround

Orientation

• Vertical axis -- up/down

up

down

above

belowupright

Orientation

Horizontal plane – Two axes:

Language and Frames of Reference

• There seem to be three prototypical frames of reference in language (Levinson)– Intrinsic– Relative– Absolute

Intrinsic frame of reference

frontback

right

left

Relative frame of reference

frontback

left??

right??

Absolute frame of reference

north

west

south

east

TR/LM and Verticality Schemas

• The book is under the table.up

down

under

Proximal/Distal Schema

.

Simple vs. Complex Schemas

Container Schema

• Roles:– Interior: bounded region– Exterior– Boundary

C

C C

TR

TR

out in

TR/LM + Container

Container Schema Elaborated

– Complexities –more roles/specifications:• Boundary properties

– Strength– Porosity

• Portals

Source-Path-Goal

Constraints:

initial = TR at Source

central = TR on Path

final = TR at Goal

Source Path Goal

SPG -- simple example

She drove from the store to the gas station.

TR = she

Source = the store

Goal = the gas station

Source Path Goal

SPG and Container

She ran into the room.

SPG. Source ↔ Container.Exterior

SPG.Path ↔ Container.Portal

SPG. Goal ↔ Container.Interior

PATH landmarks

past across along

LM

LM

LM

Part-Whole Schema

Part

Whole

semantic schema Containerroles:

interiorexteriorportalboundary

Representing image schemas

Interior

Exterior

Boundary

PortalSource

Path

GoalTrajector

These are abstractions over sensorimotor experiences.

semantic schema Source-Path-Goalroles:

sourcepathgoaltrajector

Language and Spatial Schemas

• People say that they look up to some people, but look down on others because those we deem worthy of respect are somehow “above” us, and those we deem unworthy are somehow “beneath” us.

• But why does respect run along a vertical axis (or any spatial axis, for that matter)? Much of our language is rich with such spatial talk.

• Concrete actions such as a push or a lift clearly imply a vertical or horizontal motion, but so too can more abstract concepts.

• Metaphors: Arguments can go “back and forth,” and hopes can get “too high.”

Simulation-based language understanding

Analysis Process

SemanticSpecification

“Harry walked into the cafe.” Utterance

CAFE Simulation

Belief State

General Knowledge

Constructions

construction WALKEDform

selff.phon [wakt]meaning : Walk-Action constraints

selfm.time before Context.speech-time selfm..aspect encapsulated

The INTO construction construction INTO subcase of spatial-prep

form selff .phon [Inthuw]

meaningevokes Trajector-Landmark as tlevokes Container as contevokes Source-Path-Goal as spgtl.trajectorspg.trajectortl.landmarkcontcont.interiorspg.goalcont.exteriorspg.source

Simulation specification

A simulation specification consists of:- schemas evoked by constructions- bindings between schemas

Simulation-based language understanding

Analysis Process

SemanticSpecification

“Harry walked into the cafe.” Utterance

CAFE Simulation

Belief State

General Knowledge

Constructions

construction WALKEDform

selff.phon [wakt]meaning : Walk-Action constraints

selfm.time before Context.speech-time selfm..aspect encapsulated

An experiment on Image Schemas

• Richardson and Spivey (2003) operationalized this question by presenting participants with sentences and testing for spatial effects on concurrent perceptual tasks.

• An interaction between linguistic and perceptual processing would support the idea that spatial representations are inherent to the conceptual representations derived from language comprehension (Barsalou, 1999).

Example verbs

The servant argued with the master.

The storeowner increases the price.

The girl hopes for a pony.

The athlete succeeds at the tournament.

The miner pushes the cart.

Aspect angles

• Vertical was 90 and horizontal 0.– Mean aspect angles were – (12=H, 42=Neutral, 69=V)

Example verbs

The servant argued with the master. 20 11 H

The storeowner increases the price. 85 75 V

The girl hopes for a pony. 55 36 V

The athlete succeeds at the tournament. 68 44V

The miner pushes the cart. 10 12 H

Free formForced choice

AVERAGE ASPECT ANGLE

The experiment

• Each trial began with a central fixation cross presented for 1000 ms. A sentence was presented binaurally through headphones. There was then a pause of 50, 100, 150 or 200 ms. – This randomized “jitter” was introduced, so that participants could not

anticipate the onset of the target visual stimulus. • The target, a black circle or square, then appeared in either the top,

bottom, left or right position, and remained on screen for 200 ms. • Participants were instructed to identify the stimulus as quickly as

possible, pressing one key to indicate a circle and another to indicate a square.

• Reaction times and accuracy rates were recorded. • The questions were interrogative forms of the filler sentences with an

object substitution in half of the cases (e.g., “Did the dog fetch the ball/stick?”). Participants responded “yes” or “no” by pressing designated keys.

Summary of Result

• There is an interference effect when the verb category is vertical (from norming study) and the visual stimulus object is vertical.

• Issues with the experiment?

Language and Thought• We know thought (our

cognitive processes) constrains the way we learn and use language

• Does language also influence thought?

• Benjamin Whorf argues yes• Psycholinguistics

experiments have shown that linguistics categories influence thinking even in non-linguistics task

Language

Thought

cognitive processes