Processing of kinetically defined boundaries in areas V1 and V2 of the macaque monkey

We recorded responses in 107 cells in the primary visual area V1 and 113 ce lls in the extrastriate visual area V2 while presenting a kinetically defin ed edge or a luminance contrast edge. Cells meeting statistical criteria fo r responsiveness and orientation selectivity were classified as selective f or the orientation of the kinetic edge if the preferred orientation for a k inetic boundary stimulus remained essentially the same even when the direct ions of the two motion components defining that boundary were changed by 90 degrees. In area V2, 13 of the 113 cells met all three requirements, where as in V1, only 4 cells met the criteria of 107 that were tested, and even t hese demonstrated relatively weak selectivity. Correlation analysis showed that V1 and V2 populations differed greatly (P < 1.0 x 10(-6), Student's t- test) in their selectively for specific orientations of kinetic edge stimul i. Neurons in V2 that were selective for the orientation of a kinetic bound ary were further distinguished from their counterparts in V1 in displaying a strong, sharply tuned response to a luminance edge of the same orientatio n. We concluded that selectivity for the orientation of kinetically defined boundaries first emerges in area V2 rather than in primary visual cortex. An analysis of response onset latencies in V2 revealed that cells selective for the orientation of the motion-defined boundary responded about 40 ms m ore slowly, on average, to the kinetic edge stimulus than to a luminance ed ge. In nonselective cells, that is, those presumably responding only to the local motion in the stimulus, this difference was only about 20 ms. Respon se latencies for the luminance edge were indistinguishable in KE-selective and -nonselective neurons. We infer that while responses to luminance edges or local motion are indigenous to V2, KE-selective responses may involve f eedback entering the ventral stream at a point downstream with respect to V 2.