Context effects in visual perception and their explanations

The context of a visual object is constituted by stimuli in its surround. Context effects are present when the perception of an object changes when its context changes, without any physical change in the object itself. Four classical examples of context effects of the perception of area, length, orientation, and lightness are presented in a common, structured format. A formal definition of context effects is provided. It is proposed that accounts of context effects can be classified into three explanatory strategies (psychophysical, physiological, and interpretational). A simple example of each strategy is presented (accounts based on contrast, lateral inhibition, and illumination interpretation), with special emphasis on explanations of the simultaneous lightness contrast effect. Features of these strategies are discussed, including their appealing aspects, but with a stress on their weak points