Selectivity for complex shapes in primate visual area V2.

To explore the role of visual area V2 in shape analysis, we studied the responses of neurons in area V2 of the alert macaque using a set of 128 grating and geometric line stimuli that varied in their shape characteristics and geometric complexity. Simple stimuli included oriented bars and sinusoidal gratings; complex stimuli included angles, arcs, circles, and intersecting lines, plus hyperbolic and polar gratings. We found that most V2 cells responded well to at least some of the complex stimuli, and in many V2 cells the most effective complex stimulus elicited a significantly larger response than the most effective bar or sinusoid. Approximately one-third of the V2 cells showed significant differential responsiveness to various complex shape characteristics, and many were also selective for the orientation, size, and/or spatial frequency of the preferred shape. These results indicate that V2 cells explicitly represent complex shape information and suggest specific types of higher order visual information that V2 cells extract from visual scenes.