An affordance is an action that an individual can potentially perform in their environment. (Wikipedia, nov 1 2007)
The term affordance was used by perceptual psychologist J. Gibson to describe the properties of the environment upon which one can act. They are action possibilities within an environment or the ways in which the environment allows one to interact with it.
Derived from Gibson's definition, affordance for Norman (1999) refers to the possibilities of action communicated by the environment and perceived by the actor.
Gaver (1991) like Gibson sees affordances as possible actions afforded by an object or environment as existing regardless of whether or not they are perceived but by separating affordances from their perception, elaborates on the interaction between them necessary for an action system. (Gaver, 1991, p. 80)
- Perceptible affordances exist where information on the actions that are afforded are perceptible to the user. These are very dependent on language, culture, context, experience, etc. and vary for different users.
- Hidden affordances are actions that are possible but may not be visible but may be inferred
- False affordances are present if users perceive an environment affords actions that are not possible
- Correct rejection occurs when there is neither the affordance nor the misperception of its existence.
Gaver also breaks down perceptible affordances into
- Sequential affordances - affordances revealed over time as one action reveals the possible actions that may follow
- 'Nested affordances - affordances that combined reveal a specific associated action
Affordance in user-centered design
In his book The Psychology of Everyday Things, Norman applies the term affordance to design of physical and virtual products and environments. He later makes the distinction between real and perceived affordances inherent in objects and environments, with perceived affordances being the actions users perceive are possible (or not possible in the case of non-affordances) Where physical objects contain both real and perceived affordances (e.g. a cylinder affords rolling), graphic and interface design of computer-based environments is concerned with what a user perceives to be possible or not and what actions the user infers to be potentially useful (e.g. clicking on an icon will have an effect on the system, whereas touching the screen will not, though both actions are afforded by a personal computer) (Norman, 1999)
Using Gaver's distinctions, design would be concerned with the influence it can have on both false and perceptible affordance and in many instances in instructional design or gaming design with hidden affordances that must be discovered through the former two.
- Logical constraints - reasoning to find possibilities
- Cultural constraints - learned conventions and analogies (click on a link, drag a scroll bar)
Affordance design principles
Norman (1999) suggests four basic principles to increase the perception of the affordances of screen-based environments.
- Follow major conventions already established for images and actions.
- Wherever possible, use words in addition to icons and graphics
- Use recognizable metaphors (e.g. the screen as a desktop)
- Be consistent and coherent in the use of the conceptual model behind the design (i.e. the three first principles)
However in using affordances as frameworks for designing interactions and interfaces, issues related to Cognitive load theory and the differences between novice and expert users (Expertise reversal effect) must be considered. One possible approach is to allow users to customize their environments as their expertise increases.
Distributed affordance space
From the distributed cognition perspective, the unit of analysis is the interaction between the components of the system, i.e. both the actors "internal space" and the "external space". Accordingly, Zang and Patel (2006) define affordances as distributed representations that extend across external (the environment) and internal (the organism) representations.
(Zang and Patel, 2006:Preprint, emphasis added by DKS.)
Zang and Patel (2006) then present a categorization of affordances from this perspective of distributed cognition:
- Biological Affordance
- Physical Affordance, the category Gibson and Norman were most interested in (e.g. opportunities offered by a door handle).
- Perceptual Affordance, e.g. meaning of icons, or layout of controls (do they map the thing to control)
- Cognitive Affordance. These affordances are are internalized representations (symbols) and are defined culturally (this is not too clear to Daniel K. Schneider).
- Mixed Affordance. Most affordances are of mixed type. E.g. In order to operate a coffee machine you both must understand something about coffee making (hot water + coffee power) and use the interface of the given machine.
(to be written)
- Mads Soegaard - Affordances - article at Interaction-design.org
- Affordance-based Design of Physical Interfaces for Ubiquitous Computing Environments
- Affordance (Wikipedia).
- User Interface (A template to plan UI design)
- St. Amant, Robert (1999). User Interface Affordances in a Planning Representation, Human-Computer Interaction, 14 (3) 317-354. DOI 10.1207/S15327051HCI1403_3. (AI modeling, but also provides a good overview in section 2).
- Elvins, T. T., Nadeau, D. R., Schul, R., and Kirsh, D. 2001. Worldlets: 3-D Thumbnails for Wayfinding in Large Virtual Worlds. Presence: Teleoper. Virtual Environ. 10, 6 (Dec. 2001), 565-582. 10.1162/105474601753272835
- Gaver, William W. (1991): Technology Affordances. In: Robertson, Scott P., Olson, Gary M., Olson, Judith S. (ed.): Proceedings of the ACM CHI 91 Human Factors in Computing Systems Conference. April 28 - June 5, 1991 pdf
- Gibson, J. J. (1977). The theory of affordances. In R. E. Shaw & J. Bransford (Eds.), Perceiving, Acting, and Knowing. Hillsdale, NJ: Lawrence Erlbaum Associates.
- Lintern G. (2000). An affordance-based perspective on human machine interface design. Ecological Psychology, 12(1), 65-69.
- McGrenere, J., Ho, W. (2000). Affordances: Clarifying and Evolving a Concept. Paper accepted for publication in the Proceedings of Graphics Interface 2000, Montreal, May 2000. pdf
- Norman, D. (1999). Affordance and Design. 
- Rogers Yvonne (2004) New theoretical approaches for human-computer interaction. Annual Review of Information Science and Technology 38:1, 87
- Zang, Jiajie, Categorization of Affordances, chool of Health Information Sciences, University of Texas at Houston HTML
- Zhang, J., & Patel, V. L. (2006). Distributed cognition, representation, and affordance. Cognition & Pragmatics, 14 (2) 333-341. PDF Preprint