Contributions of Principles of Visual Cognitive Scienceto AAC System Display Design

KRISTA M. WILKINSONa* and VINOTH JAGAROOb

aEmerson College and University of Massachusetts Medical School, Shriver Center, USA; bEmersonCollege and Boston University, USA

Beukelman (1991) introduced the concept of the magic versus the cost of communicativecompetence in AAC. Fundamentally, this refers to the relative effort that must be exerted (thecost) in order for AAC to be a viable communication mode (the magic). Many clinicians haveseen the magic for clients who are truly successful in using AAC; such successes have alsobeen documented in the literature. Yet until AAC is successful with each and every client forwhom it is implemented, it is necessary to continue to identify barriers to its effective use. Inthe same year, Light and Lindsay (1991) argued for consideration of principles of cognitivescience in constructing maximally useful AAC symbol arrays. In the current paper, weconsider how knowledge from one area of cognitive science, that of visual cognition, might beintegrated into AAC symbol array construction. We review four areas of visual cognitionthat might relate to the construction of AAC displays:(a) organization of stimulus arrayswithin either grids (row-column configuration) or integrated within natural scenes, (b)symbol location, (c) color and contrast, and (d) symmetry and axial orientation.

Keywords: Cognitive science; Visual processing; Symbol organization

Over 10 years ago, Light and Lindsay (1991)called for consideration of the cognitive sciencesin the design and implementation of aidedaugmentative and alternative communication(AAC) systems. Their challenge to the fieldwas to develop a systematic approach tostructuring such displays in order to maximizethe utility of AAC. Yet in general, the potentialcontributions of the principles of cognitivescience have remained largely untapped. In thispaper, we suggest some initial ways in which therich clinical framework of recommended prac-tice in AAC can be integrated with state-of-the-art methods that have emerged in the areas ofcognitive neuroscience and visual cognition overrecent years. By doing this, we hope to initiatediscussion of how principles of perception andcognition might become one consideration inthe design of visual symbol arrays for AACsystems.

BACKGROUND AND RATIONALE

The term augmentative and alternative commu-nication refers to a compilation of methods andtechnology designed to aid people whose speechcannot meet the full range of their communicativeneeds. A major component of this approach iscalled aided AAC. Aided AAC refers to modes inwhich an external aid is used to store and accesssymbols. External aids range from low-technol-ogy books of symbols to high-technology devicesin which a computer is used to store and displaythe symbols (see Beukelman & Mirenda, 1998, fordetailed introduction to AAC). Although thereare some systems that make use of auditory formsof language representation (e.g., auditory scan-ning), many others rely on visual-graphic symbolslike letters, words, or pictures. The concern here iswith those systems in which symbols arerepresented and accessed visually.

*Corresponding author. Emerson College, Communication Sciences & Disorders, 120 Boylston St., Boston, MA 02116, USA. Tel:(617) 824-8288. E-mail: Krista_Wilkinson@emerson.edu

Augmentative and Alternative Communication, September 2004 VOL. 20 (3), pp. 123–136

ISSN 0743-4618 print/ISSN 1477-3848 online # 2004 Taylor & Francis LtdDOI: 10.1080/07434610410001699717

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AAC: Costs and Magic

In a 1991 address to the international communityof AAC professionals and researchers, Beukel-man introduced an important contrast: the magicversus the cost of communicative competence.Fundamentally, this refers to the relative effortthat must be exerted (the cost) in order for AACto be a viable communication mode (the magic).Many clinicians have seen the magic for clientswho are truly successful in using AAC; suchsuccesses have also been documented in theliterature (e.g., Cafiero, 2001; Romski & Sevcik,1996; Waller, et al., 2001). Yet until AAC issuccessful with each and every client with whom itis implemented, it is necessary to continue toidentify barriers to its effective use and tosystematically investigate those factors thatspecifically enhance the magic (and reduce thecost) of AAC.Some well-documented factors contributing to

the cost of aided AAC include significantlyreduced rate of message preparation, limitationsin vocabulary size, and limited numbers ofpartners who are trained to encourage commu-nicators who use aided AAC to participate inconversation. Solutions to these limitations havebeen offered. For instance, word predictionattempts to increase message speed, generativesystems like iconic encoding respond to vocabu-lary limitations, and partner training can mitigateconversational limitations (see, e.g., Beukelmanand Mirenda, 1998, for greater detail). Yet eventhese solutions have their own costs (see Beukel-man & Mirenda, 1998).In this paper, we introduce the possibility that

both the structure of the visual symbols them-selves as well as the display upon which theyappear may affect cost and magic of AAC. Wepropose that the rich basic science of visualcognitive neuroscience might offer tips forreducing some of the perceptual processingbarriers that make the cost of visual-graphicAAC symbols too high for some individuals. Ourproposal is intended to initiate discussion thatcould lead to research collaborations.

What is Visual Cognitive Neuroscience?

The general term cognitive neuroscience refers to afield that seeks to understand cognition andbehavior in relation to underlying neural systems.Cognitive neuroscience, as it has emerged over thepast 25 years, is defined in part by its widelyinterdisciplinary nature. It draws on and inte-grates findings from the fields of cognitivepsychology, biological psychology, neuroanat-omy; and neurobiology, psychophysics, and

computer science; as well as the clinical disciplinesof neuropsychology, neurology, and psychiatry. Itfollows that researchers in the field of cognitiveneuroscience study functional domains such aslanguage; memory; vision; spatial processing;aspects of sensory and motor function; emotion;and abstract, supramodal cognition. Yet, whiletopics of interest in the discipline include a rangeof cognitive and behavioral phenomena, researchemphasis is often placed on information proces-sing aspects of cognitive and neural systems.The field has emerged and continues to thrive by

embracing a very flexible and integrative approachto expansion of the knowledge base. Cognitivetheories may inform the interpretation of clinical,neuropsychological, and neuro-imaging data frompeople with brain damage or certain neuropscy-hological conditions. Conversely, knowledgeabout neural circuits and functional neuroanat-omy and procedures such as functional neuroima-ging, may themselves be used to test or constraintheories and ideas about cognition. This may beviewed as a coevolutionary strategy, typified byinteraction among research domains, whereresearch at one level provides constraints, correc-tions, and inspiration for research at other levels(Churchland & Sejnowski, 2000, p. 14). Aneurocognitive phenomenon can be analyzed interms of discrete computations within a neuralcircuit or from the viewpoint of overt behavior.This openness and commitment to mutuallyinformative strategies has generated many levelsof analysis within the field.Because vision and spatial function are preemi-

nent functional domains of the human brain,much of the work in cognitive neuroscience hasconcentrated on visuospatial function (seeKosslyn & Osherson, 1995; Palmer, 1999;Gazzaniga, 2000). The study of visual and spatialfunctioning and its neurological foundations iscalled Visual Cognition or Visual CognitiveNeuroscience. Processes of interest include visualattention (what determines patterns of observa-tion), visual recognition (object, face and wordrecognition), spatial representation and mentalimagery and rotation (the ability to imagineobjects in space and to mentally manipulatevisual images), spatial plans for eye and limbmovements, and visual systems involved inguiding movement and action. Visual cognitivescience is a widely studied domain because it lendsitself to multidisciplinary analysis (Farah, 2000).It is studied from the perspectives of molecularneuroscience, neurophysiology, neuropsychology,cognitive psychology, computational neuro-science, and artificial intelligence.There are numerous areas in the brain

dedicated to visual perception and processing.

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They are distributed across all four of the majorlobes of the cortex as well as within subcorticalstructures, organized to form a functional hier-archy (Kaas, 2000; Felleman & Van Essen, 1991).Processing along this hierarchy can be dividedinto two large stages: (a) primary or early vision:seeing and registering a visual stimulus; theseparation of figure and background, perceivingborders, lines and surfaces, etc.; and (b) high-levelvision: using the percepts from primary vision toconstruct visual form, mentally represent and givemeaning to a visual object or scene, and mentallymanipulate the scene if required.

Why is Visual Cognitive Neuroscience Importantwith Respect to AAC?

Processing of data in visual and spatial modalitiesis central to visually-based aided AACapproaches because those systems, out of neces-sity, define a fixed frame of object-centered spacethrough the use of an external aid. Visual and/orspatial principles also come into play in virtuallyevery aspect of the aided AAC process becauseaided AAC differs in unique ways from spokencommunication. Perhaps the most obvious differ-ence is that visually-based AAC symbols involvevisual rather than auditory modes. Although it isnot fully clear how linguistic symbols withinvisual-graphic modes are processed in the brain, itstands to reason that there are at least somealterations from the processing of auditorylinguistic stimuli. Most likely, both primarylinguistic pathways as well as specific visualpathways are recruited. If so, it will clearly benecessary to understand the functioning of bothof these systems. Neither one, in isolation, willprovide a complete picture of language processingwhen a visual mode is used.Another important difference is in the organi-

zation of the lexicon. For people who use speech,vocabulary is internal, organized by the indivi-dual and stored in and accessed from his or herown memory. With aided modes, however, thelexicon is stored on and accessed from a spatially-constrained external aid, which is most typicallyorganized by a team of professionals andcaregivers. Thus, unlike spoken or signed modes,the lexicon of an individual who uses aided AACis graphically represented on an external display.Thus, visuo-spatial processing is integral even tothe most basic tasks like symbol perception (seeingthat a symbol is present on a display), discrimina-tion (being able to tell two symbols on a displayapart), identification (knowing what real-worldobject or event the symbol references) and recall(remembering that a symbol appears on a certaindisplay). In order to enhance communicative

competence, it is important to consider both theperceptual salience of the symbols themselves aswell as their organization. Visual symbols andorganization systems that impede basic proces-sing tasks are, in turn, unlikely to foster thehigher-order communication competencies thatare the fundamental goal of augmented interven-tion. Direct study of the design properties thatenhance or inhibit access and use of visualsymbols is therefore essential to the success ofAAC interventions.

Current Aim

The aim of this paper is to provide an overview ofsome of the considerations in visual cognitionthat might be relevant for AAC display design.Four areas of visual cognition that might relate tothe construction of AAC displays are considered:(a) organization of stimulus arrays within eithergrids (row-column configuration) or integratedwithin natural scenes, (b) symbol location, (c)color and contrast, and (d) symmetry and axialorientation. Each of these areas, defined anddescribed in the upcoming sections, were selectedbecause they relate directly to object-centered orallocentric visual fields such as those used in AACdisplays.It is important to note that the focus of this

paper is on one application of cognitiveneuroscience to the design of AAC displays,namely the role of perceptual structure of visualsymbols and arrays in supporting processes of on-line communication. Other important areas ofmutual interest also exist. For example, cognitiveneuroscience research on the relationship of visualsystems and higher-order processes of attention,memory, or linguistic functioning all have poten-tially significant implications for the design ofAAC displays. The focus on perceptual factors is alogical first step in this essential interdisciplinarydialog, as a means of laying the groundwork bywhich other factors may be investigated andintegrated. Similarly, although we touch on theunderlying neural bases for these phenomena,they serve only as backdrop to the current paper.The rapid emergence of visual cognitive

neuroscience has emphasized many cognitiveframeworks and neural systems that make upthe broad functional domain of visuospatialfunction (see Jagaroo, 1999). This section high-lights four elements that might be important indetermining stimulus structure and organization:symbol array considerations, symbol location,color and contrast, and symmetry and axialorientation. As noted earlier, for the purposes ofthis overview, we focus on principles of percep-tion as they influence cognition, drawing upon the

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fundamental neurological underpinnings as abackdrop to the clinical discussion.

Symbol Array Considerations: Grid versusSchematic Scene Arrays

Historically, aided symbols have been organizedinto grids, in which specific symbols occupyindividual spaces placed at regular intervals.Recently, an alternative to this traditional visualsymbol array has been offered. In the schematicscene array (Drager Light, Speltz, Fallon, &Jeffries, 2003), individual symbols like MILK areembedded within everyday-occurring contextualscenes; thus, the MILK symbol may be displayedas sitting on the table in the kitchen. The existenceof these two alternatives, grid versus schematicscene presentation, makes it important forclinicians and researchers to consider the relativeadvantages and disadvantages offered by each.In terms of simple visual display, grids offer

certain advantages. One advantage is the isolationof each stimulus in physical space. Each cell orbox in the grid may be viewed as a separatecontainer that confers on its content a degree ofautonomous identity and value. Because stimuliare individually placed into clearly demarcatedsquares, multiple regions of the space areexplicitly or subtly cued and attention is invitedto each cell. This structure potentially supportsboth perception and recall of the individualcontents of each cell.In contrast, in a naturalistic visual scene

ensemble, the relationship between objects, theirrelative positions and orientations constitute alarger cohesive visual environment. (The termnaturalistic scene is visual cognition’s equivalentof schematic scene in the AAC vernacular). In anaturalistic scene, the meaning of an object andits semantic associations are integrally tied toother objects in the scene and the holistic contextcarried by the scene. It is this holistic and familiarnature of naturalistic scenes that may offer anadvantage to younger children. As Drager andher colleagues (2003) have argued, such schematicdisplays are highly consistent with the emergenceof symbolic functioning developmentally and thusmay be more in line with the cognitive needs ofyoung children who use AAC. If so, visualsymbol arrays that make use of naturalistic scenesmay be one step toward achieving the goal ofenhancing the magic of AAC for young children.

Neuropsychological underpinnings of grid andnaturalistic scene perception

Although both grids and naturalistic scenes aremeans of displaying stimuli, from a neurocogni-

tive point of view there are some extremelyimportant differences in the way the two displaysare processed. Consequently, the two displaytypes sometimes rely on quite unique perceptualsystems. Grids are congruent with the primatebrain’s spatial system of mapping coordinates in aplanar-topic and Cartesian-like manner (seeJagaroo, 2002), and it appears that the humanperceptual system exerts some prototype andexemplar effects on grid patterns (see Blakeslee& McCourt, 1997; Greene & Waksman, 1987).Grid dynamics operate along complex cognitiveand computational principles (Jagaroo, 2002;Locher, Stuppers, & Overbeeke, 1998), and thesehave not been well researched. Presumably, theoptimum grid will depend on factors such as (a)the size or parameters (e.g., width and heightboundaries) of the visual field on which it isimposed, (b) the size of items within each cell ofthe grid, (c) the complexity of these items, and (d)the distance between the viewer and the grid.What may be the optimum grid for one set ofstimuli and under one set of viewing conditionsmay not be optimal for another set of stimuli andviewing conditions. In contrast, naturalisticscenes involve processing of parts that aremeaningfully tied to other parts to create anintegrated scene. Because of the composite orintegrated nature of naturalistic scenes, thismethod of display differs from unnaturally oruniformly distributed objects (see Meng &Sedgwick, 2001; Sigman, Cecchi, & Gilbert, etal., 2001). In particular, highly automatic,associative cognitive processes are more likely tocome into play (Fabre-Thorpe, Delorme, &Marlot, et al., 2001).As an illustration of the differences between

naturalistic scenes and grids, consider the follow-ing example. Imagine a scene of a shopping mallfeaturing a main indoor arcade, lots of littleshops, some bigger ones in the background,people of various sizes, shapes and ages holdingshopping bags, a security guard, escalators, a firehose mounted on a wall in the periphery, someframed pictures, and a narrow view of cars in theoutside parking lot. Recognizing this scene can beachieved without selective attention to any singleobject, and objects are recognized in part throughthe whole; thus, the people featured in the scenetake on the meaning of shoppers primarily fromthe context in which they appear. The visualattention given to the scene is also spreadunevenly. Some objects or features may receivemore attention than others. The presentation ofkey features (such as the mall building, shops, andshoppers) and many supporting features (such asthe elevator and security guard) collectivelyvalidate a template in the viewer’s memory.

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A useful concept for comparing grids andnaturalistic scenes is that of the power of a visualstimulus (see Ginsberg & Goldstein, 1987; Wain-wright, 1999). Within visual cognition, the termpower has a very specific and technical meaning,referring to the combination of an object’s physicalattributes as well as the extent to which itcontributes to the collective meaning of the scene.In the technical sense, the fire hose on the wall hasfar less power than the shoppers holding shoppingbags, as it is both physically and conceptually lessimportant to the interpretation of the scene.In terms of visual processing, the value or

power of each object is affected by other objects.Particularly in naturalistic scenes, where there isgreater context for interpretation of items, suchpower is unevenly distributed. In technical terms,this is called an anisotropic distribution of power(see Wainwright, 1999). In contrast to thenaturalistic scene, grids attempt to distributepower evenly. In a grid where each cell is empty,the power distribution across the grid is close toeven. (It is not entirely even because the variableof hemifield dominance may apply.) The bound-aries created by the lines or even spacing of thegrid minimize associations with other items.Hence, in the previous shopping example,pictures of a shopper, escalator, security guard,and so forth will now take on separate identities,because each appears in a single cell. Each objecttherefore calls for a minimum degree of localizedattention within a greater allocentric frame.The distribution of power will be roughly even

across a grid, provided that the visual salience ofeach item is about the same. The salience of anitem, however, is also an important consideration:For instance, irrespective of size, presentation, orother factors that influence visual power, the firehose on the wall may be highly salient to a childwith a specific interest in firefighting equipment orobjects that are colored red. Thus, for someviewers (those with exceptional interest in fireequipment), this item will have special salience.Note, however, that any distinctions in salienceshould hold within viewers, across symbolarrangement formats. That is, the increasedsalience of the fire hose for one individual willalter the distribution of power for that individualirrespective of whether the fire hose is presented ina grid or a naturalistic scene. It is in this way thatthe power of a stimulus can be distinguished fromits salience.

Implications of symbol array configuration forAAC

Visual cognition research has demonstrated thatthe grid format coerces a person to register every

object in the grid. In the naturalistic scene,however, once the viewer perceives the gist of thescene, localized attention to various objects maynot be necessary. These differences in processingdynamics constitute the most likely basis forneurocognitive differentiation between naturalis-tic and non-naturalistic scenes. Many of theprocesses involved with object perception andscene perception have been detailed by Marr(1982) and Zeki (1993). Inferring from theirwork, some cardinal processes in grid andnaturalistic scene perception may be describedas follows: Grid processing will first involve (a) ageneral mapping of the grid array and (b) object-centered processing of each stimulus item in thegrid. The object processing, in turn, will involvean extraction of the object’s main axes, percep-tion of form, configuration, boundaries andcontrasts within the object. Determining whatthe object is may demand more cognitiveresources than where the object is since the gridneutralizes the value of location (the occipito-temporal what system is likely to be much moreactive than the occipito-parietal where system;see Ungerleider & Mishkin, 1982). In perceptionof naturalistic scenes, the first principles ofprocessing likely to apply are coordinatemapping of the scheme and arrangement – theoverall configuration of the objects and theirrelative locations; determination of foregroundand background items and relative depth anddistance relations. Global features will bemapped before local (discrete detail) features.Scene mapping may require more encoding ofwhere an object lies in the scene – coding therelative location of objects in a scene.Two issues are raised by this discussion. First, it

is not clear that construction of grid-based AACarrays has taken the complexities of how humansperceive grids into consideration. Thus, it remainsessential to determine the extent to which visualcognitive factors may affect performance bypeople who use AAC whose displays areorganized in traditional grid arrays. Second, itappears that specific alterations in perception areintroduced by the naturalistic scenes. If grids andnaturalistic displays are processed differently, itwill be imperative to determine the optimalstructure for each in order to best arrange thesymbols for maximal use.

Summary

The rich clinically-derived principles thatcurrently are in place for organizing grid-basedvisual symbol arrays (e.g., Mirenda, 1985; see alsoBeukelman & Mirenda, 1998 for detailed discus-sion) may not generalize seamlessly to the visually

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more complex naturalistic scenes. Given itspotential advantages for young children (Drageret al., 2003), construction of such scene-basedvisual symbol arrays must also take into accountwhat is known about basic processing ofnaturalistic scenes. It is therefore potentiallyimportant to consider visual cognition and itseffects on stimulus perception, discrimination,and recall either for traditional grid visual symbolarrays or for the newly introduced concept ofusing naturalistic scenes. A unique opportunity isavailable to define basic principles for design inthe newly introduced naturalistic scenes, whilealso evaluating the structure of the more tradi-tional grid. Subsequently, the principles thatguide the design of both types of symbol arrayswould need to be subjected to empirical valida-tion.

Symbol Location

The location in which something appears in adisplay directly affects how well that item isperceived or recalled (Terumasa & Takeshi, 1999;Tsal & Bareket, 1999). Two main kinds ofperceptual biases can apply to parametric visualfield mapping: left-right bias, and central-periph-eral bias. From the perspective of left-right bias,an individual can have a greater pull to one halfof the visual field: For instance, a person may bedrawn more to the right visual field than the leftvisual field (see Kinsbourne, 1994; Reuter-Lorenz, Kinsbourne, & Moscovitch, 1990). Inmost individuals, this right visual field bias mayexist as part of a generalized rightward bias.Extreme manifestations of visual field biasesoccur in the neurological condition of hemispatialneglect (see Halligan & Marshall, 1991, 1998).Normally, generalized visual field biases canaffect visuospatial performance. An object placedin the left-hand side of a stimulus display, forexample, may be recalled better than if itappeared in the right-hand side.Several general principles about the role of

stimulus location on visual processing haveemerged from the work of Kosslyn (1987), amongothers. Objects with geometric configurations thatutilize vertical and horizontal axes are betterprocessed by the right hemisphere, and thus arebest presented in the left visual field. In contrast,objects of abstract form lacking clearly definingcoordinates may have a left hemisphere (rightvisual field) processing bias. Estimating thedistance between two squares, for example, canbe more accurately performed (in a tachistoscopicpresentation) if the squares are presented in theleft visual field. Comparison of two amoeba-likeobjects having exactly the same shape can be

better performed if these objects are presented inthe right visual field. In addition to Kosslyn’s(1987) findings, others have noted that processingof faces and of emotional facial expression is alsobetter subserved by the right hemisphere (Pizza-galli, Regard, & Lehmann, 1999; Sergent &Signoret, 1992). For these stimuli, performanceis therefore enhanced by left visual field presenta-tion. From the perspective of central andperipheral bias, stimuli appearing in the centerof the spatial frame can be favored over those inthe periphery, under certain conditions (see Levy,Hasson, & Avidan, et al., 2001; Malach, Levy, &Hasson, 2002).

Neuropsychological underpinnings of the stimuluslocation effect

Performance that is contingent on the visual half-field in which a stimulus is presented (left-right)has long been discussed in relation to cerebrallateralization of function (see Gazzaniga, 1987;Kinsbourne, 1994; Springer & Deutsch, 1998). Byand large, the two hemispheres of the brainbecome responsible for specific processing func-tions and therefore are differentially sensitive tothe various stimuli in the world. In a similar way,differences in central versus peripheral processingare likely to reflect the well-established findingthat retinal, occipital, frontal and parietal neuralsystems differentiate the coding of central andperipheral coordinates (Andersen, Snyder, Batis-ta, Buneo, & Cohen, 1998; Funahashi, Bruce, &Goldman-Rakic, 1990; Livingstone & Hubel,1988). Points of space across the entire visualfield are mapped by a spatiotopic coordinatesystem controlled by posterior parietal andprefrontal coordinate mapping systems (Ander-sen et al., 1998; Andersen, Snyder, Li, &Stricanne, 1993). For each point in space, andfor each stimulus occupying that space, the brainassigns an internal coordinate, thus transposingthe external space from the visual field to aninternal representational system. This kind ofmapping applies to the frame of space to whichthe viewer is attending, and in which eye and headmovements may be used for scanning andsampling the frame.

Implications of stimulus location for AAC design

Professionals continue to seek the best methodsfor organizing vocabulary. Suggestions includeorganizing by activity (snack, gym), theme (birth-day party, holiday), or word type (people, food;Beukelman & Mirenda, 1998). Within individualpages of a display, organization can be by row(foods on the top row followed by drinks and

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utensils), preference (highly preferred or mostsalient at the top), or word-class category(subjects on the left side, action labels in thecenter, direct objects on the right). Such strategiescan be useful even for constructing a simpledisplay centering on the theme of going to the petstore to adopt a cat. Imagine that there are threeline drawings to place on the display: thosecorresponding to CAT, PET STORE, andHAPPY. What factors contribute to the decisionas to how to place the symbols? An array mightperhaps be organized spatially by the type ofword. Illustrated in Panel A of Figure 1, theobject CAT in this visual symbol array would beplaced on the left, the location/destination PETSTORE in the center, while the descriptorHAPPY appeared on the right. Alternatively,the symbols might be placed in some type ofevent-based order (Panel B), with PET STOREon the left hand side, CAT in the center, andHAPPY on the right. This could then gloss to thebasic concept, ‘‘I went to the pet store to adopt acat, and now I’m so happy!’’ Such decisions areclinically sound and likely are the basis for manyorganization decisions.Can the principles of visual cognition also offer

suggestions for organization? Data cited earlier,for example, suggest that perception and recall offaces and emotion information, as well asgeometrically regular forms, are enhanced whenstimuli appear in the left visual field, whileprocessing of less abstract and amorphous stimulimay be enhanced by presentation in the rightvisual field. Among the symbols here, the face isemotionally expressive (happy). The symbol

representing CAT is curvy in form; it does nothave highly defining axes conforming to theprimary horizontal or vertical reference. Thesymbol representing a PET SHOP is very block-like in form and has well defined points ofreference corresponding to cardinal axes. Basedon the spatial principles described above, Panel Cwould be the one best attuned to optimal visualperception. It places a happy face in the left visualfield (right hemisphere), the cat in the right visualfield (left hemisphere), and the pet shop, aperceptually easy item, in the center (a neutralposition). In fact, from the standpoint of visualcognition, Panels A and B deviate from basicperceptual principles and are therefore non-optimal.Additionally, the three arrangements can be

considered from the perspective of distribution ofvisual power, which was defined earlier. To beginwith, the face is more rapidly perceptible than thestore or the cat because (a) it obeys a simpleholistic form and is an easy-to-recognize cognitiveexemplar; (b) it has a simple and striking two-color contrast scheme; and (c) it also conveys anemotional expression. Relative to the other twosymbols, the face may have greater salience nomatter where in the visual field it is placed.However, this simple difference in salience is alsopotentially affected by other factors. When placedin the right visual field, the face receives theadditional benefit of general right field dominanceor orientation bias (see Kinsbourne, 1994).Therefore, in panels A and B, with the face inthe right visual field, the total power is heavilycentered in the right visual field. In panel C, theface is in the left field and in this position justhappens to correspond well with a left field-righthemisphere bias for faces. Now, with a generalright field bias operating on a less salient object inthe right visual field, power is distributed a bitmore evenly across the panel.

Summary

Clearly, the organization of the three symbols inthis simple visual symbol array differs dependingon what factors are weighted most heavily. Thesymbol array generated by considerations ofvisual cognition offers an alternative to thosegenerated by word-type or event. Would the arrayoffered by consideration of visual cognition haveany clinical impact on AAC use? The answer tothis question is unknown. The research fromvisual cognition has resulted from basic-levelexperiments, oftentimes using very brief stimuluspresentations, that are not intended to mimic theexperiences of people using visual displays forcognitive or communication tasks. Clearly, speci-

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FIGURE 1 Examples of three possible symbol orders, basedon word type (panel A), event-based order (panel B), orpotential visual cognitive considerations (panel C).

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fic studies are necessary to determine whetherarrangements that reflect results from these basicstudies facilitate actual AAC use. Yet it is possiblethat symbol organization that maximizes basicperceptual processing could have positive effectson AAC use by reducing some of the basicperceptual costs of aided communication. Ittherefore seems reasonable to ask whethervariations in spatial location actually affectperformance with symbols commonly used onAAC boards. To what extent are these effectsenhanced or reduced in grid versus naturalisticscene arrays, given their specific differences? Howdo the kinds of disabilities that lead to AAC usealter these effects?

Color and Contrast

Color and contrast are two primary dimensionsof stimulus encoding that come into play at earlystages of visual processing. Color information isinitially used to segment the visual scene and laterfacilitates image retrieval. Long-term visualmemory is enhanced when color and form arebound in the memory representation (Hanna &Remington, 1996). Because even the simplest line-drawings in AAC systems can incorporate color,it is essential to examine the effect of color andcolor contrast.The role of color in design of AAC displays has

been debated in clinical practice for some time,particularly after the introduction of color inthe commercially available Mayer JohnsonPCSTMsymbols in the 1990’s. However, a searchof Academic Search Premier, ERIC, andPsychArticles databases in the spring of 2003revealed that this clinical conversation has neverbeen translated into direct research attention. Toour knowledge there are no articles in which thepotential negative or positive effects of manip-ulating symbol color in AAC displays have beenreported. In the only related article, Bailey andDowning (1994) reported that color accenting ofsymbols assisted learning of symbol meaning bychildren with multiple disabilities. This finding isconsistent with research in visual cognitive sciencethat has demonstrated repeatedly that color canaffect a number of cognitive processes, from basicperceptual discrimination through learning andrecall (Davidoff, 1991, 1997). In general, colorappears to have a facilitative effect on processing.In light of the clinical interest within AAC andthe substantial database available in visualcognition, the absence of systematic study of therole of color in AAC is at best surprising, and atworst a fundamental oversight that could inad-vertently contribute to less-than-maximal displayconstruction.

Neuropsychological underpinnings of the effect ofcolor and contrast

Much of the data on color vision as it applies toAAC design may be described in terms ofspatiochromatic properties of the visual systemand the stimuli being perceived. Color informa-tion is initially used in perception to segment thevisual scene and aid image contrast (Gegenfurtner& Rieger, 2000). In object perception, visualshort-term memory could be enhanced whendifferent colors code different features of theobject. Xu (2002), for example, had participantsview mushroom shaped objects in which each oftwo components (cap and stem) were of differentcolors. Color enhanced short-term memory foreach part at an individual level (e.g., better short-term memory was demonstrated for one of thecolored parts over another). Color also plays arole when two objects are grouped together. Inlong durations of exposure, for example, simila-rities in surface color may facilitate object group-ing (Schulz & Sanocki, 2003). Although similarfindings hold for exposures of short duration,Shulz and Sanocki (2003) have suggested thatdifferent neural mechanisms underlie the short-and long-duration processing. Color informationis also used for image retrieval during recall tasks.Long-term visual memory is enhanced when aparticular color is associated with a particularform, and a memory representation is builtthrough this binding of color and form (Hanna& Remington, 1996). Recognition of pictures isenhanced when their shading and details arerendered in color (Wurm, Legge, Isenberg, &Luebker, 1993).A substantial body of research has examined

the effects of color on visual processing in theperception of naturalistic scenes. These studieshave shown that participants recall more informa-tion about naturalistic scenes when the originalscene included color than when it was presentedin black and white (Wichmann, Sharpe &Gegenfurtner, 2002). Interestingly, no advantageor disadvantage was found for scenes in which thecolors were artificially altered. The spatiochro-matic properties of some natural scenes (e.g., redfruit against green leaves as opposed to yellowfruit and brown trees) correspond easily and moresynchronously to red-green receptor and repre-sentational systems of the primary visual system(Parraga, Troscianko, & Tolhurst, 2002). Thismeans that color can be a factor contributing toattention or speed of perception. When used incertain ways, such as to emphasize the features ofan object or to bring about contrast between anobject’s features, color adds perceptual salience toan object or scene. Perceptual salience heightened

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by color may enhance pattern perception andshort-term memory (see Sperling, Reeves, Blaser,Lu, & Weichselgartner, 2001) and the effect ofcolor in enhancing attention varies with imagetype (Parkhurst, Law, & Niebur, 2002). Studies ofchange blindness using a flicker paradigm, inwhich participants are asked to identify whatchanges across two versions of a scene, havedemonstrated that participants accurately identifythe change more rapidly when it involves color asopposed to form (e.g., Carlin, et al., 2003).Little research exists on the variable of color in

the perception of grids; however, one phenomen-on called the contingent color aftereffect, or theMcCollough effect (McCollough, 1965; see Allan& Siegel, 1997), may be of relevance to the designof grid-based displays. This is a color after-effectin which the color lying beside vertical andhorizontal line gratings, presented in alternatingsequences, manifests a perceived after-effect whenthe stimuli are withdrawn. It is thought that thelines (the orienting stimuli) act on the visualsystem’s edge-detection mechanisms to producethese orientation-contingent color after-effects(seeMcCollough, 1965). Whether AAC-style gridscan manifest any similar effects during the normalcourse of presentation is simply not known.

Implications of color and contrast for AACdisplay design

Perhaps the most fundamental question iswhether color enhances or detracts from symbolperception, learning, or recall. As describedpreviously, color assists in the segmentation of avisual scene; it brings out contrasts betweenobjects and it highlights details; it enhancesperceptual discrimination, and it cues memoryfor objects. In view of this, it seems intuitive thatcolor aids the processing of AAC symbols innaturalistic scenes. (One may choose to minimizethe use of color under certain circumstances, forexample, if the aim is to examine shape or globalform processing only and where minimal empha-sis is needed on details and intra-object features.)The same may not be true for grids, however,

because grids lack the background contextualinformation of naturalistic scenes. Grids, there-fore, reduce the amount of context within whichthe symbols appear. As a result, color may takeon a different role. Consider, for instance, theobservation reported earlier that in longerdurations of exposure, similarities in surface colormay be used for object grouping. If this is thecase, then non-relevant similarities in color, whenpresented in grid form, may become distractionsor may impede discrimination of similarly-colored items. In the example illustrated in Figure

2, the colors of the cap available in the PCSdictionary are either blue or red. Consider ease ofidentification of the cap (and potentially, recall) ifits color was consistent with other clothing items(within-category consistency; panel A of Figure 2)or not (outside-category consistency, Panel B).

Summary

As with location, according to the principles ofvisual cognition, color may in fact play animportant role in perception, learning, and recallof AAC symbols. In this case, color may play verydifferent roles in grid versus naturalistic scenedisplays. In naturalistic scenes, a major considera-tion could be the extent to which color offers asupportive or distracting cue. In grids, it may beimportant to determine the extent to which theMcCollough effect interferes with perception andlearning. For both, the question of color place-ment illustrated in the figure likely comes intoplay. What are the optimum color schemes whenpresenting complex visual stimuli either within agrid format, where each stimulus occupies its own

FIGURE 2 Example in which a target symbol color matchesto related items (cap matches other clothes; panel A) orunrelated items (cap matches fruit; panel B).

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space, as compared to a naturalistic scene? Whatare the best permutations for color/form combi-nations in AAC displays? Research is necessary toaddress these basic, yet thus far under-researched,questions.

Symmetry and Axial Orientation

Symmetry and axial orientation refer to thestructure of a stimulus itself (symmetry) andhow it is aligned (axial orientation). A symmetricstimulus has relatively even halves, which areessentially mirror images of one another. As anexample, the upper-case letter X is symmetricwhereas J is not. Symmetry typically applieseither for left and right halves or for top andbottom halves. Thus, whereas X is symmetric inboth directions, M is symmetric only for left-righthalves and B is symmetric only for top-bottom.Axial orientation refers to the orientation of anobject’s main axes in planar space. Many objectshave a predictable orientation; trees generallygrow vertically. Returning to the example ofletters, consider the uppercase letter N. Figure 3presents this letter in three orientations; itsaccepted orientation (on the left), rotated slightly(in the center) and rotated 90 degrees (on theright). Deviated from its accepted orientation theletter is less recognizable or, in the case of 90degree rotation, is a different letter altogether. Ina letter recognition task, recognition of the middleN will take a few microseconds longer thanrecognition of the first N. People with mentalrotation difficulties will take even longer with themiddle N. Clearly, axial orientation makes asignificant contribution to interpretation of visualstimuli.

Neuropsychological underpinnings of thesymmetry and axial orientation effects

Perhaps because symmetry and orientation arefeatures occurring in nature, the perception andapplication of symmetry and orientation havebeen coded into human evolution and cognition.As with basic effects of location, these are wiredearly on in development, and thus potentiallyrelevant for even very young children respondingto a perceptual display.Shepard and Farrel (1985), Just and Carpenter

(1985) and Kosslyn (1987, 1994) have offered

extensive descriptions of the role of stimulusconfiguration and orientation in visuospatialperception. They have made several observations.One is that simpler images make for easier, rapidjudgments, whereas multipart objects call forgreater encoding and slower discriminationbetween objects. As noted earlier in the sectionon symbol placement, symmetrical objects with ageometric square-like configuration with easilyidentifiable coordinates may have a right hemi-sphere (left visual field) processing bias; thus,these might be best perceived when placed on theleft-hand side of the display. Another is thatorientation is important. Images orientated to thecanonical (vertical and horizontal) axes areprocessed more easily than multi-axial or offsetimages.

Implications of symmetry and axial orientationfor AAC design

Construction and alignment of stimuli on either agrid-based or a scene-based AAC array could beinformed by an understanding of principles ofsymmetry and orientation. AAC visual systemscan utilize cardinal orientations to imposemaximum stability on a perceptual scene orobjects in a grid. Stimulus items can be configuredand arranged in consideration of multiple vari-ables: alignment of axes of symmetry, thesimplicity of global structure of a stimulus item,maximization of canonical axes, and the visualfield in which abstract versus elementary shapesappear. When a natural scene is presented, mostof the objects in the scene can be positioned suchthat they are aligned to major (horizontal andvertical) axes. This would especially benefit therecognition of smaller or more minor objects inthe scene. Similarly, in a grid presentation, thealignment of objects can be made as canonical aspossible and the objects’ configuration can bekept to the simplest reasonable level. The axis towhich an object is aligned can also be manipu-lated to bring about salience in certain presenta-tions. Highlighting one object in a grid ornaturalistic scene, for example, can be achievedby aligning it with a very non-canonical axis suchthat it will deviate from its typical orientation.

Summary

To what extent do symmetrical or nonsymme-trical stimuli enhance perception, learning, orrecall in AAC? How does canonical versusnoncanonical orientation of symbols affect thesefactors? What factors will enhance perception ofall of the objects in a scene, and what factors willdraw attention to one important object? To our

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FIGURE 3 Example of the role of axial orientation on symbolinterpretation.

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knowledge, these questions have never beenasked. Yet they would seem critical not just toitem selection but also to item arrangement.

DISCUSSION

Professionals who design AAC systems currentlyhave several options to guide their choices ofsymbol types as well as visual symbol arrayorganization (e.g., Beukelman & Mirenda,1998). These are clinically useful tools that havehad much success with many individuals whouse AAC. Despite advances in both technologyand understanding of principles of AAC, thecost of AAC remains very high for manyindividuals (Beukelman, 1991). Is it possiblethat some of these costs may relate to displaysthat do not maximize visual-perceptual salienceof the items? We have argued that the principlesof visual cognitive science can help to informdisplay design, either in naturalistic or grid-based arrays. The ultimate validity of thisargument is an empirical matter. Given itspotential, it seems essential to explore thepossibility through systematic research. It is alsoimportant, as in any effort to bridge disciplinaryboundaries, to acknowledge some of the ques-tions that arise as the process of evaluating therelevance of a very basic science (visual cognitivescience) for a very applied discipline (AACdisplay construction) begins. In this finaldiscussion, we evaluate some of the remainingchallenges to this effort and identify additionalquestions for research beyond those articulatedpreviously.

How Relevant are the Basic-Science Findings forClinical Practice?

The findings introduced thus far have beenobtained from basic research, oftentimes withstimuli that, by design, are presented for briefperiods. Why might they nonetheless be impor-tant in considering AAC device display, eventhough such devices allow the symbol to remainvisible for long periods of time? There are twomain reasons – one developmental and onepractical.From a developmental standpoint, the simple

kinds of mappings discussed previously arecontrolled by hard-wired primary visual mechan-isms that operate even at birth (see Purves &Lichtman, 1985). More complex mapping ofcoordinates within each half field is a higher-levelvisuospatial process involving the posteriorparietal and prefrontal cortices (see Andersen etal., 1993; 1998). These more complex systems are

also hard-wired early on, although they canimprove with age and experience. Because thesevisual processing skills are in place very early,they might be expected to be relevant toprocessing of visual displays even in the youngestchildren, but certainly for older individuals aswell.From a practical standpoint, an intuitive

criticism is that aided symbols would not besubject to the influences of basic perceptualdifferences like those identified here because theyare fixed in place on a communication aid.Consequently, there is no a priori time limit;individuals who use devices can observe a displayfor as long as they desire. Although true, it is alsotrue that this fixed nature of symbols may notcharacterize actual acts of aided communicationfor all individuals. In order to locate symbols,individuals with gross motor limitations who havedifficulty maintaining a steady head position maymerely glance at their display prior to initiating amessage. For them, the display can be considereda flashing target, not because the symbolsthemselves move but rather because the percep-tual system does. For other individuals who havedynamic display systems, the device allowsexplicit movement from one virtual page to thenext. An individual, therefore, must flash throughseveral pages on his or her way to a desireddisplay; thus again, the symbols are not static, butrather shift as each page replaces the next. Forthis reason, it seems reasonable to at least askwhether the well-established principles fromvisual cognition might have an effect for AACdisplay design.

What About the Effects of Neuropathology onApplication of the Principles?

The basic principles discussed have been derivedprimarily from studies of individuals with noclinical disabilities. By definition, however, candi-dates for aided AAC have some (identified orunknown) cause for their inability to rely onspeech as the primary mode of communication.Most likely, many if not most of these causesinvolve some level of neuropathology. To whatextent do the principles of visual cognition applyin clinical populations that most typically useAAC displays?Clearly this is a very important question, and

again one that warrants systematic empiricalattention. The fact that the answer to thisquestion is, as yet, unknown, should not be causefor abandoning an effort to apply principles ofvisual cognition. What is known of clinicalpopulations thus far suggests that the principlesare in fact relatively robust across many clinical

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conditions (see Heilman & Valenstein, 1993;McCarthy & Warrington, 1990). Systematicresearch within populations who use AAC, withspecial attention to the implications for AAC,would hold promise both for informing thescience of visual cognition but also the applica-tion of aided AAC.

What Would Research in this Area Provide?

It is possible, based on the material reviewed inthis paper, that systematic integration of princi-ples of visual cognition might reduce the cost ofaided AAC symbol use by maximizing thesalience of symbols. By itself, this would be animportant contribution to the ever-increasingbase of knowledge in AAC. In addition, muchmore is known in the field of visual cognitionabout the differences in processing of grid-basedversus naturalistic images. It is this area in whichthe interdisciplinary approach proposed in thispaper might most positively influence clinicalpractice in the design and construction of visualsymbol arrays. Naturalistic scenes have thepotential to revolutionize array organization, atleast for some subgroups of individuals who useAAC (Drager et al., 2003). Yet the rich clinicalknowledge base that has served well for grid-based arrays may need refinement when trans-lated into naturalistic scenes. Integration of theextensive literature on visual cognition may be avaluable asset for managing this important andtimely effort.

Acknowledgements

Preparation of this paper was supported in partby NICHD HD 35015. Many thanks to NancyBrady, Michael Carlin, and Celia Rosenquist forreviews of early versions; and to Neha Shah andEmily MacDougal for assistance in preparation.

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