Abstract
A single spatiochromatic signal is able to describe both chromatic and luminance cosine gratings by varying the spatial phase of that signal. This signal representation allows psychophysical chromatic and luminance spatial contrast sensitivity functions (CSFs) to be described as linear combinations of two global spatiochromatic mechanisms with Gaussian spatial profiles. Variations in the configuration of these mechanisms are able to account for the changes in shape of psychophysical luminance spatial CSFs as the average luminance of the grating stimulus decreases. Specifically, the shape changes can be modeled by increasing the spatial extent of a global center mechanism while decreasing the inhibitory effect of a global surround on that center as luminance is decreased. These variations are in accord with physiological findings in single retinal ganglion cells. The model also correctly predicts that decreasing luminance levels should not affect the shape of psychophysical chromatic spatial CSFs.
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