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In: Spatial Vision
In: Spatial Vision
In: Spatial Vision
In: Spatial Vision
In: Spatial Vision
Author: Adam J. Reeves

This book is an inspiring summary of Grossberg’s life work toward understanding the neural basis of the mind. Grossberg devotes many sections to deep and critical analyses of the many areas in which cognitive neuroscience has made great progress, which include sensory systems such as vision and hearing, perception, learning, memory, emotion, motivation, and various pathologies such as schizophrenia and melancholia. His approach is to use mathematical models based on combinations of short-range random processes, such as Gaussian summation, with long-range deterministic equations, the latter predominating in explanation. The deterministic aspect means his models are open to detailed testing, rather

In: Multisensory Research
In: Spatial Vision
In: Spatial Vision

We show that true colors as defined by Chevreul () produce unsuspected simultaneous brightness induction effects on their immediate grey backgrounds when these are placed on a darker (black) general background surrounding two spatially separated configurations. Assimilation and apparent contrast may occur in one and the same stimulus display. We examined the possible link between these effects and the perceived depth of the color patterns which induce them as a function of their luminance contrast. Patterns of square-shaped inducers of a single color (red, green, blue, yellow, or grey) were placed on background fields of a lighter and a darker grey, presented on a darker screen. Inducers were always darker on one side of the display and brighter on the other in a given trial. The intensity of the grey backgrounds varied between trials only. This permitted generating four inducer luminance contrasts, presented in random order, for each color. Background fields were either spatially separated or consisted of a single grey field on the black screen. Experiments were run under three environmental conditions: dark-adaptation, daylight, and rod-saturation after exposure to bright light. In a first task, we measured probabilities of contrast, assimilation, and no effect in a three-alternative forced-choice procedure (background appears brighter on the ‘left’, on the ‘right’ or the ‘same’). Visual adaptation and inducer contrast had no significant influence on the induction effects produced by colored inducers. Achromatic inducers produced significantly stronger contrast effects after dark-adaptation, and significantly stronger assimilation in daylight conditions. Grouping two backgrounds into a single one was found to significantly decrease probabilities of apparent contrast. Under the same conditions, we measured probabilities of the inducers to be perceived as nearer to the observer (inducers appear nearer on ‘left’, on ‘right’ or the ‘same’). These, as predicted by Chevreul’s law of contrast, were determined by the luminance contrast of the inducers only, with significantly higher probabilities of brighter inducers to be seen as nearer, and a marked asymmetry between effects produced by inducers of opposite sign. Implications of these findings for theories which attempt to link simultaneous induction effects to the relative depth of object surfaces in the visual field are discussed.

In: Seeing and Perceiving
In: Spatial Vision