Cortical and perceptual processing of naturalistic visual structure

The perception of complex visual patterns emerges from neuronal activity in a cascade of areas in the primate cerebral cortex. Neurons in the primary visual cortex (V1) represent information about local orientation and spatial scale, but the role of the second visual area (V2) is enigmatic. We made synthetic images that contain complex features found in naturally occurring visual textures, and used them to stimulate macaque V1 and V2 neurons. Most V2 cells respond more vigorously to these stimuli than to matched control stimuli lacking naturalistic structure, while V1 cells do not. fMRI measurements in humans reveal differences in V1 and V2 responses to the same textures that are consistent with neuronal measurements in macaque. Finally, the ability of human observers to detect naturalistic structure is well predicted by the strength of the neuronal and fMRI responses in V2 but not in V1. These results reveal a novel and particular role for V2 in the representation of naturally occurring structure in visual images, and suggest ways that it begins the transformation of elementary visual features into the specific signals about scenes and objects that are found in areas further downstream in the visual pathway.