Neural correlates of boundary perception.

The responses of neurons in areas V1 (17) and V2 (18) of anesthetized and paralyzed rhesus monkeys and cats were recorded while presenting a set of computer-generated visual stimuli that varied in pattern, texture, luminance, and contrast. We find that a class of extrastriate cortical cells in cats and monkeys can signal the presence of boundaries regardless of the cue or cues that define the boundaries. These cue-invariant (CI) cells were rare in area V1 but easily found in V2. CI cortical cells responded more strongly to more salient boundaries regardless of the cue defining the boundaries. Many CI cortical cells responded to illusory contours and exhibited the same degree of orientation and direction selectivity when tested with boundaries defined by different cues. These cells have significant computational power inherent in their receptive fields since they were able to generalize across stimuli and integrate multiple cues simultaneously in order to signal boundaries. Cells in higher order cortical areas such as MT (Albright, 1992), MST (Geesaman & Anderson, 1996), and IT (Sary et al., 1993) have previously been reported to respond in a cue invariant fashion. The present results suggest that the ability to respond to boundaries in a cue-invariant manner originates at relatively early stages of cortical processing.