A physiological adaptation model and its predictions for different color induction effects

Abstract

The appearance of a visual stimulus depends not only on the stimulus itself but also on other surrounding and remote stimuli. Induction (simultaneous contrast) and contrast induction are among the important appearance phenomena related to the spatial surrounding effects. Induction is the psychophysical phenomenon of the change in the appearance of a color (or an achromatic stimulus) caused by the presence of a surrounding stimulus. Color contrast induction is the modulating effect of the surrounding contrast on the perceived contrast of the central area (1). Color contrast is the distance between colors on a perceptual uniform color space, such as that of Demngton et al 1984, (2). The "intermixed effect, i.e. the smaller perceived effect of a variegated surround vs. a homogeneous surround while the surround is composed of the same average chromaticity and intensity at both surround areas has also been studied (3). These color and color contrast effects have been tested by many groups. However, their physiological mechanism and computational aspects are in dispute or not known. Color induction (first order of color adaptation) is widely accepted to be associated with the very well known phenomenon of color constancy (a psychophysical phenomenon in which the system can partly discount illumination chromaticity). In this study we attempt to claim and demonstrate that color induction is an epi-phenomenon of color constancy, since the same mechanism cause both effects. Contrast induction (adaptation of the second order) is suggested as a mechanism for enhancing the differences in contrast surfaces or objects. Thus, both mechanisms serve for enhancing the differences between the stimulus and its surrounding area.We'suggest a comprehensive computational model based on the retinal (opponent) and cortical (double-opponent) color-coded receptive fields (RF) and on first order (retinal) (43) and second order (cortical) adaptation mechanisms (6). As far as we know, there is no previous suggested comprehensive model in the literature which describes all these induction effects and no previous biological model has succeeded in predicting color constancy and color enhancement or the color contrast of real images (4,6). 2.The Model 2.1. Responses of three types of On-center color-coded cells, the first order from the cones through several processing layers. These cells have a color-opponent receptive field with a centersurround spatial structure. (A receptive field (RF) is that region in the visual field from which a visual stimulus will elicit a response.) The cells considered here belong to the three most common color-coded types in the retina, they are labeled L+M', M'L-and S+(L+M)-, with L, M and S standing for long, medium and short wavelength sensitivity.The spectral composition of the light reaching the retina when an illumination falls on the surfaces of objects and is reflected from them is the input to the cones level. The quantum catch of each of the three cone types, L-$, &and S , , . , is expressed by an inner produ...