ABSTRACTWe present a new way of conceptualising tangibles forlearning . This scheme adopts Heidegger's analysis of theways a user can treat a tool : either as 'ready-to-hand' or`present-at-hand' . It also proposes two types of activity alearner can engage in when using a tangible : eitherexploratory or expressive activity . Finally, two types ofmodels that a user can explore are proposed : theoreticaland practical models .Examples from the literature are described in terms of thisframework and an example is given from our own work ofan attempt to use this conceptualisation in design .

KeywordsTangible, conceptualisation, learning, external cognition,embodied interaction

INTRODUCTIONThe `tangible' approach to design is becoming increasinglyviewed as an alternative to the traditional graphical userinterface. Inspired by Weiser's vision of computationremoved from the desktop box [30], and exploitinginnovation in sensing technology, researchers arebeginning to explore the coupling of physical objects withdigital information to support users engaged in a diverserange of activities [12, 15] . Different design frameworkshave been applied to the development of these systems,resulting in a rapid growth in applications, including theuse of physical objects as tokens to access digitalinformation [14], the use of generic physical objects ascontainers to move information between devices [27], andtangible interfaces where physical artefacts are used toboth represent and control digital information [26] . Anexample of a system designed in this spirit is Underkofflerand Ishiis' Urban Planning (URP) workbench [29], wherephysical models of buildings can be manipulated on a tabletop to explore what shadows might be cast at differenttimes of the day, and how different configurations mightinfluence the pattern of airflow, through dynamic

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li in

tangibles to support learning

Paul Marshall, Sara Price and Yvonne RogersInteract Lab

School of Cognitive and Computing SciencesUniversity of SussexBrighton, BNI 9QH

paulma@cogs.susx.ac .uk

visualisations projected onto the space. The term tangiblehas been used in various ways, but is adopted in this papergenerally to describe all examples of physical objectsaugmented with digital information . .One of the goals of our research has been to look toemerging technologies as a source of inspiration forconceptual development [24] . To this end we are exploringthe potential of tangible technologies to support learning .In particular we aim to highlight differences betweentechnologies and styles of interaction with tangibles and toexplore educational implications .In his recent book Where the Action Is, Dourish [12] hasdescribed the tangible approach to computing as part of anhistorical movement in HCI to design user interfaces thatexpand the range of human abilities available wheninteracting with computers. Specifically, he suggests thattangible (and social) approaches to computing allow workto be embodied ) in the everyday environment . Dourish'snotion of embodiment emphasises the role of practicalengagement with the world in the creation and sharing ofmeaning. This contrasts with what has been the dominantparadigm in cognitive science and HCI, namely a Cartesianseparation of cognition and action, with an emphasis onobjective rational thought.

The characterisation of embodiment as a state of directengaged action has its roots in phenomenologicalphilosophy, particularly in Heidegger's notion of`readiness-to-hand' 2 [13] . This concept refers to the waythat when working with a tool or representation we treat italmost as if it were invisible; instead focussing upon thetask it is used for. Dourish's notion of embodiedinteraction, at its heart, is about how meaning is coupled toobjects, actions and representations. He argues thattechnologies designed in this way must communicate to theuser how they are coupled to the world, allowing them tobe viewed at multiple levels of meaning. The physicalmodels in Underkoffler and Ishii's URP [29] could for

I The notion of embodiment is explored more generally inClark l l l ] .

2 The terms "ready-to-hand" and "present-at-hand" wereoriginally introduced into the HCI literature by Winogradand Flores [31]

example be viewed by the user as objects in their ownright, as symbolic representations of real buildings, or astools for manipulating an airflow simulation .

However, as Chalmers [9] has recently pointed out,Dourish overemphasises the concept of 'readiness-to-hand' leading to a neglect of Heidegger's complimentarynotion of 'presence- at-hand' : attention to the tool orrepresentation as an object in its own right. We agree thatthis imbalance in emphasis is a weakness of Dourish'sembodied approach, particularly when the goal of thetechnology is to facilitate learning . Instead, we adopt theperspective of Ackermann ( l, 2, see also 10], that effectivelearning often involves temporarily standing back from thelearning experience to reflect upon it in more objectiveterms, as Chalmers points out, exactly the sort of"rationalising, objectifying, and abstracting activity" [9]that Dourish contrasts with the embodied approach . Weshare with Dourish a wish to design embodied artefacts thatwill allow users to act through them in engaging activity .However, our focus on learning technologies suggests thatin order to learn from experience, to exploit generalitiesand links between learning domains, children need toremove themselves from it periodically to reflect upon it asseparate from self [1, 2, 10]. Augmenting physical artefactswith digital capabilities opens up the space of possibleactivities that children can engage with in this manner.

We have found the concepts of 'readiness-to-hand' and`presence-at-hand' useful for thinking about the differentmodes of interaction supported by tangibles for learning .However, despite this, and although there has been aproliferation of new technologies in recent years [e .g . 19,26-29], the tangible approach remains underspecified interms of conceptual frameworks that might be applied todesign decisions. In this paper we describe some conceptsthat we have found useful in describing and designingtangibles for play and learning . We see all well designedtangibles as supporting an embodied ready-at-handinteraction . However, we also point to differences in theway users can attend to the tangibles in a present-to-handmanner . In so doing we hope to provide some initial ideasto inform the design of tangible systems for differentactivities . We propose two main classes of tangiblesystems : expressive and exploratory .

Expressive tangible systemsOne class of tangibles embodies aspects of the user'sactions with the system . Thus, when users attend to thetangible as present-to-hand, they can focus on an externalrepresentation of their own activity . We suggest, in linewith a theory of external cognition [25], that representingactivity in an external representation can aid objectivereflective thought and support learning . By making explicittheir own understanding of a topic, learners can make clearinconsistoncies, conflicting beliefs and incorrectassumptions (t0, 18] . As the learners create their ownrepresentations, we term this class of tangibles expressive :

a categorisation adopted from Mellar and Bliss' [18]discussion of the ways children can learn with scientificmodels .

Exploratory tangible systemsThe second class of tangible interface does not embody theuser's activity . We suggest that when attending to this typeof tangible as present-at-hand, the user will be more likelyto focus on the way the system works, rather than reflectingon the history of their own interaction with it. We adopt theterm exploratory [18] to describe this class of tangible, asthe learner explores a model presented by someone else .

We can see two types of reflective learning that couldderive from this class of tangible . First, the learner canlearn to use the tangible itself for some task . The learningin this case would be highly situated [6, 16]. That is, howto use a particular tool in a particular context. We call thistype of reflective attention to the tangible practical. It canbe exemplified by the type of question the learner mightask himself or herself. For example, "What can I do withthis system?" Second, the tangible could encapsulate sometheoretical model of the world. We call this way oforienting to the tangible theoreticalj . In this situation, thelearner explores the model through their interaction withthe tangible . As the model encapsulated in the systemmight be different to the learner's own mental model, thenlearning might be expected to result from a comparisonbetween the two world views [7] . The type of question thelearner might ask in this context could be "How does thismodel relate to the real world?"

The tangibles classification scheme that has beendeveloped here describes two ways that learners can orientto the system : they can treat the tangible as ready-at-hand,working through it to complete a task, or they can focus onthe tangible itself, treating it as present-to-hand. Wesuggest that productive learning results from a cyclebetween these two attentive styles . We also suggest twokinds of activity that the learner can engage in, which haveimplications for the manner in which they focus on thetangible : expressive activity, where the tangible willembody in some way the learner's behaviour, eitherphysically or digitally, and exploratory activity, where thetangible embodies a model provided to the learner by thedesigner. Finally, we suggest two ways that the learner canexplore a model provided by the designer : eithertheoretically, where the model embodies some theoreticaldescription of the world, or practically, where the learnermight reason about the mechanisms by which the tangibleinterface works. In the next section four examples of

3 Although situated cognition theorists might balk at adistinction between theoretical and practical learning, webelieve there to be a meaningful difference . However, itmight be better represented as a continuum of abstractionrather than as categorical : an idea proposed by CarlBereiter [5]

tangibles f'or learning will be introduced and analysed interms of this framework.

TANGIBLES FOR LEARNINGChromariumChromarium is a mixed reality activity space that usestangibles to help children experiment and learn aboutcolour mixing [23] . The framework developed in thecourse of this work looked at the notion of transforms :changes to the state ofthe world relative to actions upon it .Four types of transforms were investigated : physical(action)-physical (effect), physical-digital, digital-physical,and digital-digital . Of interest here is the physical-digitaltransform, where changes in the physical orientation ofmulticoloured cubes augmented with RF-tags and placedon a tag reader, provoked changes on a digital displayshowing the effect of mixing the colours on the cube faces(see figure 1) .

Figure 1 : Chromarium - physical actions producedigital effects [231The tangibles used in the Chromarium system were foundto support a fluid, embodied interaction . Children wereable to interact with the coloured cubes as ready-to-hand,rapidly combining and recombining colours withimmediate visual feedback . The type of present-at-handattention supported by the Chromarium system was alsoexploratory and largely practical : the system has a fixedmodel of possible interactions, and it is the child's task toexplore these possibilities . This characterisation issupported by the kinds of reflective discussion andactivities that Rogers et al. [23] report children to engagein . In particular it was found that they spent much timeexploring the parameters of the interface, for example,putting their faces on the tag reader, expecting them to beprojected onto the screen, and pressing down on the cubesin the expectation that this would make the colours on thescreen appear darker .In their comparison of different types of transforms,Rogers, Scaife et al. [23] found the coupling of a familiarphysical action with an unfamiliar digital effect to beeffective in getting the children to talk about and reflect

103

upon their experience. This finding is of importance for ourframework, as it suggests that tangible-based learningmight be particularly effective in getting children toalternate between the present-at-hand and the ready-to-hand .

Illuminating LightIlluminating Light (28] is a system designed at MIT toallow the rapid prototyping of laser-based optical layouts .The system comprises a large workspace where tangibleelements representing objects like lasers, lenses and mirrorscan be manipulated . The system senses the orientation ofthese elements and projects dynamic simulations of laserlight onto the workspace surface (see figure 2) .The Illuminating light system affords the user the potentialto engage in a ready-at-hand interaction, working with theobjects to produce different patterns of light . In ourframework, the kind of present-to-hand attention the usercan pay to the system is exploratory, as the user ispresented with a model of optics to explore and where nokind of history of interaction is constructed . It is alsotheoretical as the model is a simulation of how patterns oflaser light might be produced in the real world. The design,like the Chromarium, suggests that tangibles can supportboth ready at hand and present to hand interaction .

Figure 2: Illuminating Light [281

TeIlTaleTeIlTale is a tangible system that allows young children topractice literacy skills through oral language [3, 4] . A toycaterpillar was designed, comprising of a number ofmodular segments, each of which allows a short soundrecording to be made and which can be rearranged in anyorder (see figure 3) .

Children use the recording facility of TeIlTale as a tool tocreate short oral stories, finding the recording interfacestraightforward to use [4]. Thus, the focus of their attentioncan be directed through the toy to the recording and story-telling task : an engaged, ready-at-hand interaction .

Figure 3 : TellTale system [3, 4]

Two aspects of Te1ITale's design support reflection by thechildren on the storytelling activity. First of all, the systemallows the children to record their composition in anexternal medium . In the framework we have beenproposing this can be seen as an expressive activity .Making digital recordings facilitates the separation oflanguage from the context in which it is created [17],aiding more objective present-to-hand attention to thestory. The ability to think about language removed fromcontext is an important predictor oflater literacy [8] .

The second aspect of TellTale's design, relevant to theframework being developed here, is its physical form .TellTale embodies the segmented and linear structure oftraditional narrative [e .g . 20] . Focussing on the structuralelements of the toy's design provides children with a modelof narrative to explore. A comparison of the storiesproduced by children with segmented and non-segmentedversions of the toy showed that children playing with thesegmented version produced longer and more cohesivestories with more traditional story endings compared withchildren playing with the non-segmented version [8] . Interms of our framework this supports present-to-handtheoretical activity through the use of the caterpillarstructure .

SummaryWe have briefly reviewed four tangible-based learningsystems, describing each in terms of our tangibleframework. We have seen that all support both `embodied'ready-at-hand, and more `removed' present-to-handactivity . The colour mixing task in Rogers, et al.'s [23]Chromarium study presents learners with an unfamiliarform of interaction to explore and make sense of.Underkoffler acd Ishiis' [28] Illuminating Light presentsusers with a theoretical model of optics to explore andprototype systems with . Fourthly, Ananny's [3, 4] TellTaleboth provides young children with a structural model oftraditional narrative and allows them to interactexpressively, recording and listening to their own oralnarratives .

In the next section we describe our attempt, using thisframework, to design a tangible-based system to promotereflection within a larger digitally augmented learningexperience . The project called the Ambient Wood [22],was designed to help children learn scientific skills whileon a field trip in a digitally augmented environment .

DESIGN OF ATANGIBLE LEARNING SYSTEMWe designed a large-scale learning experience, called theAmbient Wood, based around the idea of a digitally-augmented field trip [22] . The project aimed to helpchildren learn about the nature of scientific enquiry throughdiscovery, reflection, and experimentation . Pairs of 11-12year old children initially explored different habitats in alarge woodland environment, taking light and moisturereadings and having information about the organisms livingin the wood `pinged' to them on PDAs, relative to theirlocation [21] . In this way they received augmentedinformation about organisms they could see in the wood aswell as those that were inhabitants but not readily visible tothe children, for example, caterpillars and woodlice .

We used our tangible framework to design an activity forthe second Phase of the learning experience, gettingchildren to reflect upon and consolidate the knowledgethey had gained both from their physical exploration of thewood and from information they had received on theirPDAs while doing the exploring. We specifically wanted tosupport children in thinking about the relationships andinterdependencies between the organisms they hadobserved . Thus, we wanted pairs of children to compare theinformation they had about two different habitats in thewood. This would provide them with further information,requiring them to collaborate and discuss . In so doing, wewanted to facilitate them in transferring from the concrete(of their explorations) to the abstract (of their conceptualunderstanding), to move from the focussed individualpieces of information they had found to a more holisticunderstanding of the ecosystem. This phase was to takeplace in a `den' : an informal classroom-type environmentin a marquee erected in the wood itself.In line with our framework we focussed on activities thatallowed both embodied activity, where the tangible wastreated as ready-to-hand, and a more reflective present-at-hand attention to the activity embodied in the tangible . Tothis end, we conceived of a tangible system that childrencould use to collaborate in constructing a picture of thewoodland habitats they had explored . Through thisexpressive activity, we hoped the children might makeexplicit their understanding of the relationships betweenorganisms they had discovered in the habitats . However,we were concerned that simply constructing a picture ofthewoodland might not be enough to make children thinkdeeply about the relationships between organisms. Thus,we decided to also incorporate elements of an exploratoryactivity . This was to take the form ofthe system monitoringthe children's activity in relation to its own model of the

ecosystem and informing them when they either deviatedfrom this model or when they incorporated elements thatcould be related at a higher level of abstraction. Thus, forexample if the children incorporated pictures of brambles,and a type ofbird called a chiff-chaff, the system played ananimation showing the chiff-chaff nesting in its naturalhabitat under the brambles . If on the other hand, thechildren placed thistles in the woodland habitat. (where theydid not grow), the system alerted the children to theirmistake and asked them to try again.

Two studies were carried out to develop and determine theeffectiveness of our system based on the tangiblesframework.

Study 1The first task we designed was one where children had touse digitally augmented tokens to build up an externalrepresentation of the two habitats in the wood . The twopairs of children were required to each build up a picture ofthe habitat they had explored in the wood by placing RF-tagged tokens representing the organisms on a tag reader .We were initially interested in having the children explorethe notion of change over time, so one tag readerrepresented the wood in autumn, while the otherrepresented the wood in spring . Placing a tagged tokenwould cause a picture of that organism to appear on a largedisplay, representing both habitats in the wood . By makingexplicit the composition of the wood in different seasons,the aim was to enable the children to better understand thechanging relationships between organisms.

Figure 4 : Materials used in study 1

(Top - paper cut-out `display', bottom left - some of the

tokens used, bottom centre and right - `tag readers'

representing seasons)

In order to develop this task and provide concrete design

solutions, a low-tech version was initially produced . Plastic

tokens were created with pictures of the organism they

linked to printed on top. Paper cut-outs of the organismswere also produced to mimic the pictures that would appearas visualisations on the display in response to a token beingplaced on the RF-reader (see figure 4) .

MethodA study was designed where pairs of 11-12 year oldchildren were first asked to imagine they were exploring awood while they walked around the school playground .Images ofthe organisms found in the wood were presentedto the children on a PDA coupled with information such aswhat the organism eats, where it lives/grows etc. The aimof this part of the study was to mimic the exploration phaseof the ambient wood experience itself and to put thetangible task in context. Images of the organisms found in awoodland habitat were presented to one pair of children,while images from a clearing habitat were presented to theother pair .

The pairs were then brought together in a large room in theschool . The children were asked to work together to buildup a picture of what the two habitats would look like firstin autumn (the time of year the study was carried out) andthen in spring . The children performed this task by placingthe plastic tokens on the relevant `RF-reader' . Anexperimenter played the role of the computer placing papercut-outs of organisms on the mock display. The childrenwere encouraged to both work together and to talk abouttheir reasons for placing each token .

FindingsFindings from this low-tech study were particularlyrevealing about the sort of activity necessary to engagechildren in the task using the tokens in a ready-to-handmanner. The children did not find the activity of placingtokens on the RF-reader to be a particularly engaging one,often just throwing the tokens down on the reader withvery little thought as to why they were placing them in thatparticular location .

We reasoned that this lack of engagement might be due tothe children having little control over the placement of thepaper cut-outs on the display and the manner of interactionnot being direct enough to support the kind of embodiedactivity we wanted to support. This prompted us to

redesign the way the children interacted with the paper cut-outs in the second half ofthis study. Instead of having themplace the tokens on the RF-reader, we asked the children totake over the role of the experimenter, placing the paper

cut-outs on the mock-up display.

The children found this activity to be much more engaging

than the last. They discussed the placement of the cut-outs

to a greater extent and talked about some of therelationships between organisms . For example:

Cl :

"Where shall we put the trees?"

C2 :

"Put the trees there, so you can put the chiff-chaff onthem ."

Cl : "Butterfly . . ."C2 : "Stick it on the bluebells. Make sure you stick it the

right way up this time".

We concluded from this study that embodied interactionwas better supported in the task, when children were ableto work directly with the representations themselves, ratherthan controlling the placement of the representations moreindirectly through the placement of more abstract tokens .

Study 2Based upon our findings from the first low-tech study, weredesigned our task to allow children to work more directlywith representations of the organisms in the wood . Insteadof having the children build up a picture on a displaythrough placing tagged tokens on a reader, we decided tohave them work with representations of the organismssimilar to the paper cut-outs used in the low-tech study.This was accomplished by printing pictures of theorganisms onto static-cling film . This film could then bestuck onto a shiny board with areas representing thehabitats in the wood . In order to link the placement of thesepictures to the computer model of the habitats, small RF-tags were attached to each of the pictures and two RF-readers were placed behind the two areas on the boardrepresenting the clearing and woodland habitats . A displaywas placed next to the board. This set up is shown in figure5 .

Figure 5: Set up used in study 2

MethodThis study was run as part of the larger Ambient Woodproject (see Rogers, et al [22] for a more detaileddescription of this project) . At this stage of the learningexperience, the children were introduced to the tangiblesystem . RF-tagged pictures printed on static-cling filmwere laid out on a table in front of a board with two areasrepresenting the woodland and clearing habitats . Afacilitator showed the children how to stick the picturesonto the board, and to describe the relationships between

the organisms. The children were then asked to worktogether to complete pictures containing all of theorganisms that lived in each habitat . The children wereencouraged to give reasons for each picture they stuck tothe board, and to describe the relationships between theorganisms. The system was designed to provide feedbackin the form of animations and sounds if the children eitherstuck a picture in the wrong habitat, or if they stuck acombination of pictures that could be related at a moreabstract level.

FindingsFindings from the second study suggest the potential oftangibles for supporting recollection and discussionbetween the children . With little encouragement from theexperimenter, the children used the tokens on the table as afocus for a discussion about what they had found in thehabitats they had explored as shown in the followingexample:

Cl : "Wesew a woodlouse"C2 :

"We found a thistle"

C1 :

"We found moss . . . came up on our screen and itgrows in dark damp areas"

This finding supports our suggestion that focusing on therepresentational form of the tangibles in a present-at-handmanner might facilitate reflection and discussion betweenthe children. Some comparisons between the two pairs as tothe organisms they had encountered were also made . Forexample :

C1 :

"I

saw a butterfly, a white

one. . just in

there[points to wood]

C2 :

"We didn't see any butterflies . We saw birds . . ."However, the task was not as successful as we had hopedin encouraging the children to construct an externalrepresentation of the two habitats . In terms of ourframework, this was largely due to technical and practicalissues . First, the static-cling film in the outdoorenvironment rapidly became quite dirty, making it verydifficult to get the pictures to stick to the board. Thisresulted in the children spending most of their timeattending to the pictures in a practical present-at-handmanner, focussing on the pictures as a difficult to use tool,rather than working through the tool in the embodiedconstruction task we had designed .Secondly, the link between the placing of a picture on theboard and the triggering of a contingent animation provedto be a temperamental one. Thus, the children were oftenunable to make the link between their ready-to-handactivity and the exploratory model embodied in the system .Another issue that arose from this study was theimportance of context in engaging children in a tangibletask . Whereas, the children in study 1 had found the pictureconstruction task to be an engaging one, the children instudy 2 found it to be less so . This may be due to its

relationship to the rest of the ambient wood experience. Inthe first stage of the experience, the children had gainedinformation in two ways : by actively probing the light andmoisture readings in the wood, and by passively receivinginformation on a PDA relative to their location in thewood . The tangible task in the den was designed to help thechildren make links between the information that they hadreceive passively, which in this context they found lessinteresting than the information they had gatheredthemselves and which we propose they had a greater senseof ownership over . This suggests the importance ofattention to the ways in which children receive or interactwith information for future work : For example, a moreactive role for the children, to be in line with our focus onembodied interaction .

DISCUSSIONWe have seen from the two studies presented in the lastsection that an attention to the ways in which physicalartefacts support ready-at-hand interaction is crucial to thedesign of a tangible learning system . To engage children ina task, it is not enough for a system to just be tangible . Aswe saw in the first study, it is also crucial that the tangiblebe designed in a way that is appropriate to the task .Children found the placing of tokens on an RF-reader to betoo far removed from the task of building up a picture totreat the tokens as ready-to-hand . It was necessary to makethe children's engagement with the representation muchmore direct, in accordance with our emphasis on embodiedinteraction .

In the second task simple practical problems were enoughto interfere with the children's ready-at-hand interactionwith the tangibles . Instead the children focussed on thetangibles as a problematic tool in a present-at-hand manner,weakening their level of engagement.

We have also seen the importance of context in theimplementation of a tangible for learning . A tangiblelearning system that works in a classroom context may nottransfer readily to a different setting, e.g . the outdoorlearning environment of our ambient wood, where this wasone activity was embedded in a whole experience . Wesuggest that this may relate to the way children orient to theinformation being manipulated in the tangible .

CONCLUSIONWe have presented a nascent conceptualisation of tangiblesdesigned to support learning and given examples from theliterature and our own work on how it might be applied .This scheme comprises three levels of description that canbe used to determine how a tangible might be used in alearning system . First, we have proposed that tangibles forlearning should be analysed in terms of their ability to be, ready-to-hand' and 'present-at-hand' . We have suggestedthat productive learning will result from the learner cycling

between these two viewpoints, acting both through the

tangible, and focussing on the tangible itself. Second, we

have proposed two styles of interaction with a tangible :

107

exploratory activity, where the learner investigates a modelpresented by the designer of the task, and expressiveactivity, where the learner works to produce an externalrepresentation or artefact. We have suggested in line with atheory of external cognition [25] that through expressiveactivity, the learner can make explicit their ownunderstanding of the domain of study, highlightingmisconceptions or gaps in their knowledge. Throughexploratory activity with a tangible, learners can gain anexperiential understanding of a model of a knowledgedomain . We have also highlighted a distinction betweentheoretical and practical models that learners can explore.Theoretical exploration is of a model of external reality, asin the model of optics underlying Underkoffler and Ishiis'[28] Illuminating Light. A practical exploration of a modelwill be of the manner in which it can be interacted with, asin Rogers, et al.'s (23] Chromarium .

Of course these categories need not be mutually exclusive .Ananny's TellTale system [3, 4], for example, allowslearners to interact both expressively, recording oralstories, and in an exploratory manner, focussing on thestructure of traditional narrative embodied in the physicaldesign of the toy. Our own attempt to design a tangiblesystem as part of the Ambient Wood experience [22] triedto engage the learner in both exploratory and expressiveactivities . We consider this style of interaction to havemuch potential for the design of learning experiences .

Further work is required however, to both extend and fleshout this categorisation . For example, there has been littleattention to the differing roles of physical and digitalrepresentations in tangibles . We aim to develop a morecomplete framework to suggest concrete design solutionsfor the role of tangibles in learning and to build theoryabout tangible interaction .

ACKNOWLEDGMENTSThis work was funded as part of the EPSRC Equator IRC.We thank all of our partners from Nottingham, RoyalCollege of Art, Southampton and Sussex who wereinvolved in the Ambient Wood Project, particularly thoseinvolved in designing the `den' experience : Eric Harris,Ted Phelps Hilary Smith, Danae Stanton, and MiaUnderwood. This paper is dedicated to the late Mike Scaifewho continues to inspire us .

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