Phase-Dependent Interactions in Visual Cortex to Combinations of First- and Second-Order Stimuli.

Abstract

Many visual cortex neurons exhibit orientation-selective responses to boundaries defined by differences either in luminance or in texture contrast. Previous studies have examined responses to either type of boundary in isolation, but here we measured systematically responses of cortical neurons to the spatial relationship between superimposed periodic luminance-modulated (LM) and contrast-modulated (CM) stimuli with contrasts adjusted to give equated responses. We demonstrate that neuronal responses to these compound stimuli are highly dependent on the relative phase between the LM and CM components. Diversity in the degree of such phase dependence could help to disambiguate different kinds of boundaries in natural scenes, for example, those arising from surface reflectance changes or from illumination gradients such as shading or shadows.