one determines the optical flow (which can be described as the apparent flow of the movement of objects in the visual field relative to the observer) using the pattern of light on the retina. The term 'affordance' refers to the opportunities for action provided by a particular object or environment. This concept has been extremely influential in the field of design and ergonomics: see for example the work of Donald Norman who interacted with Gibson and who adapted Gibson's idea of affordances (with significant conceptual amendments) to industrial design. In his later work (such as, for example, The Ecological Approach to Visual Perception (1979)), Gibson became more philosophical and criticised cognitivism in the same way he had attacked behaviorism before. Gibson argued strongly in favour of direct perception and direct realism (as pioneered by the Scottish philosopher Thomas Reid), as opposed to cognitivist indirect realism. He termed his new approach ecological psychology. He also rejected the information processing view of cognition. Gibson is increasingly influential on many contemporary movements in psychology, particularly those considered to be post-cognitivist. One of the most important statements in this book is that Gibson maintains that the optical information of an image is not an impression of form and color, but rather of invariants. A fixated form of an object only specifies certain invariants of the object, not its solid form. (p. 227) Meaning that there is far more information available to our perceptual systems than we are consciously aware of, which may lead us to puzzle over 'invariances' that our visual or other systems easily solve. Gibson did work on perception with his wife, Eleanor J Gibson. Together they proposed perceptual learning as a process of seeing the differences in the perceptual field around an individual. An early example of this is the classic research study done by Eleanor Gibson and R. D. Walk, the visual cliff experiment. In this experiment an infant that was new to crawling was found to be sensitive to depth of an edge. Ecology and perception Gibson believed that the environment and animals are not separable items. He stated that without the environment animals cannot survive and without animals there is no environment. The environment is what we perceive at any given moment. All animals are able to perceive. Humans perceive the environment directly. This is why we are unable to perceive things in the environment that are too