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Gibson’s theory of direct perception affordances

The concept of affordances, originally proposed in Gibson’s “information pick-up” theory of perception, has received a great deal of attention (e.g., Greeno, 1994). In this case study, we examine the details of this concept and discuss why it is important.

Gibson rejected the notion that the study of visual perception should focus on the physical properties of objects in the environment. Instead, he focused on the idea that, when people view an object, they do not see its physical, molecular structure but rather its function. In this way, Gibson held that trying to understand visual processes without reference to the way in which animals interact with their environments can lead to a false understanding. Gibson defined affordances as follows: “… the affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill” (Gibson, 1979, p. 127). An affordance has three main properties:

1. An affordance exists relative to the action capabilities of a particular actor. This means that an object can be perceived as having a certain use or function depending on the capabilities of the actor (the term “actor” is used to refer to the perceiver). Gibson used the example of a flat, long, rigid surface that can afford support for one person but may not afford support for another. Suppose you want to cross a muddy patch without getting mud on your shoes. You look around and there are several objects lying about. A plank of wood would afford support for you if it was the right size, was not porous and was strong enough to hold your weight. The same plank might not offer affordance to someone of a heavier weight. The point is that the concept of affordance is an interaction between the object and the perceiver’s capabilities. Another point is that, although the plank of wood may have been designed for something else, it still offers the affordance of support in this case.
2. The existence of an affordance is independent of the actor’s ability to perceive it.This statement means that the affordance of an object is invariant and does not depend on it being perceived or detected. It is a property of the object and the current situation.
3. An affordance does not change as the needs and goals of the actor change. This is a similar point to the previous one and emphasises the invariance of an affordance. It means that the particular affordances of an object are always present, even if the individual cannot detect them. In this way affordances are objective, in that they do not depend on interpretation, value or meaning. A plank can offer the affordance of support independent of the meaning or interpretation that the perceiver attaches to it. At the same time, without the presence of the perceiver, the affordance is meaningless. So, in the plank example, the plank’s affordances do not exist separately from the actor. In other words, an object’s affordance results from an interaction between it and the perceiver. Further, when an affordance exists and there is no physical barrier to its detection, direct perception is possible. This means an affordance can exist regardless of the individual’s experiences – for example, a hidden door in a wall panel affords the opportunity to move into another room, even though the person may not see it. However, detection of an affordance can depend on experience and culture (e.g., suspecting that there is a hidden door and finding it). The individual has to learn to discriminate the information in order to detect affordances. Learning is seen as a process of discriminating between the patterns of information in the environment rather than as something that is used to supplement perceptual processes. A further point implied by Gibson’s theory is that affordances are binary – an affordance either exists or it doesn’t.

There has been some debate about the nature of affordances as described by Gibson. For example, Norman (1988) questions whether an affordance can ever exist outside perception. A designer, for example, may design a novel object whose function is immediately obvious to the user, and thus the designer and the user are using prior knowledge and experience.

McGrenere and Ho (2000) use the example of the design of a door to highlight the problems with Gibson’s and Norman’s views. Suppose there is a door with no handle and no flat panel. In order to know how to open the door, one would need previous experience with this type of door. According to Gibson’s definition, the fact that the door can be opened means that it has an affordance, even though the actor may have no idea how to open it. According to Norman, however, its affordance only exists when the user has prior knowledge of how to open it – the action possibility of the door needs to be conveyed to, or perceived by, the user. One implication of this is that an affordance may not be binary, as Gibson described. An object may have an action possibility, but this may be hard to detect (e.g., a hidden door) or hard to achieve (e.g., a flight of stairs that afford ascent but are very difficult to climb because they are covered in snow, for example).

This debate is not just about two schools of thought nit-picking over details that are irrelevant in the real world. On the contrary, it has been extremely useful for designers wanting to develop “user-friendly” products and services (McGrenere & Ho, 2000). By studying the affordances of objects, designers can produce better designs. Gaver (1991) discusses how Gibson’s ideas emphasise the importance of two things about design: the real affordance of an object, such as what it is used for, and its perceived or apparent affordance, or the design that suggests an affordance. When the real and apparent affordances match, then the artefact is easy to use and the instructions for use can be at a minimum; when they mismatch, errors are common and extra instructions will be required.

References

Gaver, W.W. (1991). Technology affordances. CHI’91 Conference Proceedings: 79–84.

Gibson, J.J. (1979). The ecological approach to visual perception. Boston, MA: Houghton Mifflin.

Greeno, J.G. (1994). Gibson’s affordances. Psychological Review, 101: 336–42.

McGrenere, J. & Ho, W. (2000). Affordances: Clarifying and evolving a concept. Proceedings of Graphics Interface 2000, Montreal, May 2000. Available online.

Norman, D.A. (1988). The psychology of everyday things. New York: Basic Books.

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