Neuronal responses to texture-defined form in macaque visual area V2

Human and macaque observers can detect and discriminate visual forms defined by differences in texture. The neurophysiological correlates of visual texture perception are not well understood and have not been studied extensively at the single-neuron level in the primate brain. We used a novel family of texture patterns to measure the selectivity of neurons in extrastriate cortical area V2 of the macaque (Macaca nemestrina, Macaca fascicularis) for the orientation of texture-defined form, and to distinguish responses to luminance- and texture-defined form. Most V2 cells were selective for the orientation of luminance-defined form; they signaled the orientation of the component gratings that made up the texture patterns but not the overall pattern orientation. In some cells, these luminance responses were modulatedby the direction ororientationofthe texture envelope, suggestinganinteractionof luminance and texture signals. We found little evidence for a "cue-invariant" representation in monkey V2. Few cells showed selectivity for the orientation of texture-defined form; they signaled the orientationofthe texture patterns and not that of the component gratings. Small datasets recorded in monkey V1 and cat area 18 showed qualitatively similar patterns of results. Consistent with human functional imaging studies,our findingssuggestthatsignalsrelatedtotexture-defined forminprimate cortex are most salientinareas downstreamofV2. V2 may still provide the foundation for texture perception, through the interaction of luminance- and texture-based signals.