Functional organizations underlying illusory and kinetic contour processing in early visual cortices V1 and V2 of macaques

Abstract

The abutting line illusion and motion defined boundary are among the most frequently used second-order patterns in visual neuroscience and psychological studies. However, the processing of illusory and kinetic contours has been surprisingly difficult to localize within the visual pathway. With our home made in vivo dual Optical Imaging rig, the functional organizations of V1 and V2 in 4 macaques have been systematically charted for abutting line illusory contour (IC) and white-noise defined kinetic grating (KG) stimuli. We have observed clear modular assemblies of cells in V1 and V2 responded to IC and KC stimuli. By closely examination of the spatial alignments of these orientation domains activated by moving luminance sinusoidal gratings (sLG), IC and KG through pixel by pixel comparison, we found that the orientation domains in V1 and V2 activated by IC stimuli were only partly in register with those activated by real contours of drifting luminance gratings of the same orientation. In contrast, the movement of white-noise kinetic gratings (KG) produced orthogonal orientation domains instead that were actually elicited by first-order local motion within KG stimuli. By directly comparison with real contour stimulus of sinusoidal gratings, the signal strengths were relatively much weaker for both IC and KG responses in V1 and V2, as expected. Our observations revealed that the functional organization and cortical mechanism in V1 and V2 for processing IC is fundamentally different from those of KG, which involve direction selective neuron populations from segregated processing channels. Thus these data indicate that the motion defined boundary is most likely processed in the dorsal pathway while the illusory contour is processed in the hierarchical stages above V1 and V2 in the ventral stream of macaque. Correspondence: [e-mail]