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TECHNOLOGY AFFORDANCESWilliam W. GaverRank Xerox Cambridge EuroPARC61 Regent StreetCambridge CB2 lAB, U.K.gaver.europarc@ rx.xerox.comABSTRACTEcological approaches to psychology suggest succinctaccounts ofeasily-used artifacts. Affordances are propertiesof the world that are compatible with and relevant forpeople’s interactions. When affordances are perceptible,they offer a direct link between perception and action;hidden and false affordances lead to mistakes. Complexactions can be understood in terms of groups of affordancesthat are sequential in time or nested in space, and in termsof the abilities of different media to reveal them. Iillustrate this discussion with several examples of interfacetechniques, and suggest that the concept of affordances canprovide a useful tool for user-centered analyses oftechnologies.KEYWORDS: ecological perspectives; human interfacedesign; input/output design; multi-mediaINTRODUCTIONThere is a real tension between tasks and technologies ininterface design. Designs based primarily on the features ofa new technology are often technically aesthetic butfunctionally awkward. But equally, designs based primarilyon users’ current articulated needs and tasks can overlookpotential innovations suggested by new technologies. Wemust understand the needs and abilities of prospective users.But equally, we must understand the capabilities andlimitations of technologies in order to know thepossibilities they offer for design.In this paper, I explore the notion of aflordances asa wayof focussing on the strengths and weaknesses oftechnologies with respect to the possibilities they offer thepeople that might use them. The term “affordance” comesfrom the perceptual psychologist J. J. Gibson [9, 10], whoPermission to copy without fee all or part of this material isgranted provided that the copies are not made or distributed fordirect commercial advantage, the ACM copyright notice and thetitle of the publication and its date appear, and notice is giventhat copying is by permission of the Association for ComputingMachinery. To copy otherwise, or to republish, requires a feeand/or specific permission.@ 1991 ACM 0.89791-383-3/91 /00(34/0079 ...$1 =J)developed an “ecological” alternative to cognitiveapproaches. The cognitive approach suggests that peoplehave direct access only to sensations, which are integratedwith memories to build up symbolic representations of theenvironment and its potential for goal-oriented action. Thisaccount has recently come under attack, particularly for itsdecontextualized approach to design [e.g., 4, 17, 19]. Infoeussing on perception, action, memory and problem-solving “in the head,” its descriptions of action in theworld, tool-use, perceptual y-guided learning, etc., oftenseem baroque and overly complicated.In contrast, the ecological approach stresses relevanthuman-scaled objects, attributes and events and the patternsof energy that provide effective perceptual informationabout them. It eschews detailed accounts of informationprocessing as being unnecessary products of the abnormalsituations found in laboratories. In focussing on everydayperception and action, the ecological perspective may offera more succinct approach to the design of artifacts thatsuggest relevant and desirable actions in an immediate way.Cognitive approaches, from this perspective, are bestreserved for artifacts which are complex, difficult to use,and error-prone.The notion of affordances is in many ways the epitome ofthe ecological approach, encapsulating ideas aboutecological physics, perceptual information, and the linksbetween perception and action. In this account, affordancesare the fundamental objects of perception. People perceivethe environment directly in terms of its potentials foraction, without significant intermediate stages involvingmemory or inferences. For instance, we perceive stairwaysin terms of their “climbability,” a measurable property ofthe relationship between people and stairs. The workrequired to climb a flight of stairs can be described by a U-shaped function relating work to riser height and leg length.Warren [18] showed that people’s visually-guidedjudgments of the climbability of different staircases reflectthis function with great accuracy: people perceive theaffordance of stairclimbing.An affordance of an object, such as one for climbing, refersto attributes of both the object and the actor. This makes79the concept a powerful one for thinking about technologiesbecause it focuses on the interaction between technologiesand the people who will use them. However, the conceptraises issues from many different domains: perception andaction, metaphor and learning, and techniques for input andoutput. A simple example from everyday life can illustratethe sorts of issues that must be addressed before the notionof affordances can be made precise and useful.WHAT AREAFFORDANCES?The concept of affordances is not a new one for design.Most notably, Norman [15] applied the concept to everydayartifacts. For instance, thin vertical doorhandles affordpulling, while flat horizontal plates afford pushing (Figure1).A.B.:ixss%$L...?~~;~~*\$&,.-~~:i,,.,.,.,.........................!.*M::::::W<::.<........................,.,...,.,.,,,.<.:;$.:::*:::::.:.:...,.,,,,,,,,.,,,,=...:.:.~.,.,*.:<.X.:.:.:::::,=<W.:,.. ............3<.~.>::,:::::::,:::::,:::::m< ::::;:!::>~:::::,;;,II F,:,:.’.’.,.,.,.:.:.~:,:,:...,:,:,:.:.:,:..........~m:,::::::::.............................................................:<.,.,..............................,,:.:.>:.~;~:~,.:.,.:.:::,:,:,:,,::,.:.,.:.,..*.,:,:::,:~~~f:::::::,,,,..:,:.:.:,:.::::,:,+::::‘.,::,.:?,,::::::>::::f:::;:m.+:~,,,,,,,,,,,,,,,,:,:,,,:.:.:.:,,:.:.,,,,,,,,,.,,,.............................:+:.:..............................................................;.~j:~,:::::::::~::,:,:,:,:,:,:,..............................3‘~:$.y::=:::::...............>.....*.~,.,..........::::::::.:::.:.x.:.x.,.,,,:.:.:.:.:.:.::............................,.,.,,,.,.,.,,,,..:.,.............................i:?.?.::,::::.:,:.::::s::;>$.:<jy,.:?.+.:.,.,.,:::,:,::::::............................................,,:,:,,:::,::::::,:,::::::::::::::,.:.:.,.,.,.:.:.:,:,,.,.,..,,.,.,..........................,...,.,:,.,.,.,.,.,:,.,:,.:::::::-:.:.:.::.~:$j...:..Figure 1. Dijjferent door handles suggest affordances fordifferent actions.The interaction of a handle with the human motor systemdetermines its affordances. When


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