According to Gibson (1977), an object directly offers its behavioral meaning to the observer. This is called `affordance'. Gibson (1977) defined that ``the affordance of anything is a specific combination of the properties of its substance and its surfaces taken with reference to an animal'' (p. 67). Thus, affordances are, for example, a rigid surface affording support (`step-on-able'), or a chair being `sit-on-able' for humans. What an object affords depends not only on the characteristics of the object, but also on the perspective of the animal. For example, a chair for a bird is not `sit-on-able', rather it is `stand-on-able'. Affordances thus link action to perception.
Gibson's concept of affordances stimulated work on the role of action in perception, and also highlighted the importance of ecologically valid information (in contrast to the simplified visual input used in many laboratories) (Gordon, 1989). However, the concept was also criticized for not explaining how experience changes animals, and for ignoring experimental work on visual processing (Gordon, 1989).