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Heller, J.

On the perception of achromatic colors: Wallach’s ratio principle revisited

It is commonly assumed that the perception of achromatic colors in center-surround configurations is governed by Wallach’s ratio principle. Within the received view, assuming that perceived achromatic colors form a continuum from black to white, this principle states that the color of the center depends on the center to surround ratio of physical intensities, but not on their absolute values. On the basis of a generalized Fechnerian representation the paper explores the theoretical consequences of various psychophysical invariances: Wallach’s ratio principle and illumination invariance as well as generalizations that may be conceived as near-misses to these conditions. It is shown that these invariances constrain the possible form of the psychophysical functions. Reanalyzing classical data in the light of these theoretical results reveals that only predictions derived from the near-miss to Wallach’s ratio principle and from illumination invariance can account for key features. The implications of these findings are discussed.

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