Affordance

Definition

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 the environmnent. Affordances are 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.

Affordance in user-centered design

In his book The Pshychology 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, ????)

Constraints

• Logical constraints - reasoning to find possibilities
• Cultural constraints - learned conventions (click on a link, drag a scroll bar)

Affordance principles

Norman (1999) suggests four basic principles to increase the perception of the affordances of screen-based environments.

1. Follow major conventions already established for images and actions.
2. Wherever possible, use words in addition to icons and graphics
3. Use recognizable metaphors (e.g. the screen as a desktop)
4. 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.

Related articles

Human-computer interaction, User-centered design, Intelligent learning environment, Open-learner model

References

• 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 [[1]]