Contrast and assimilation: The role of perceptual organization

In the visual world, the perceptual features of an object are affected by the context in which that object is perceived. An increase in perceived similarities between the object and its surround is called an assimilation effect, whereas an increase in their perceived differences is called a contrast effect. Gestalt scientists used the belongingness principle to explain both phenomena. Benary (1924) proposed that perceptual belongingness produces lightness contrast. On the other hand, Fuchs (1923) concluded that belongingness produces chromatic assimilation. In order to account for this paradox, we tried to identify the most important differences between Fuchs and Benary displays (Agostini, Galmonte, Righi, 2007), that could be responsible for the diverging results. In conclusion, the crucial factor determining lightness contrast or assimilation seems to be the level of ambiguity of the belongingness status, and the intentionality or the spontaneity of the perceptual organisation, which is a consequence of the stability level of the belongingness status.