Response profiles to texture border patterns in area V1

Cells in area V1 of the anesthetized macaque monkey were stimulated with la rge texture patterns composed of homogeneous regions of line elements (texe ls) with different orientations. To human observers, such patterns appear t o segregate, with the percept of sharp boundaries between texture regions. Our objective was to investigate whether the boundaries are reflected in th e responses of single cells in V1. We measured responses to individual texe ls at different distances from the texture border. For each cell, patterns of optimally or orthogonally orientated texels were adjusted so that only o ne texel fell into the receptive field and all other texels fell in the vis ually unresponsive regions outride. In 37 out of 156 neurons tested (24%), texels immediately adjacent to a texture border evoked reliably larger resp onses than identical texels farther away from the border. In 17 neurons (11 %), responses to texels near the border were relatively reduced. Border enh ancement effects were generally stronger than border attenuation effects. W hen tested with four different border configurations (two global orientatio ns and two edge polarities), many cells show ed reliable effects fur only o ne or two configurations, consistent with cells encoding information about the orientation of the texture border or its location with respect to the s egmented region. Across the sample, enhancement effects were similar for al l texture borders. Modulation by the texture surround was predominantly sup pressive; even the responses near texture borders were smaller than those t o a single line. We compared these results with the results of a popout tes t in which the line in the receptive field was surrounded by homogeneous te xture fields either orthogonal or parallel to the center line. The patterns of response modulation and the temporal onset of differential responses we re similar in the two tests, suggesting that the two perceptual phenomena a re mediated by similar neural mechanisms.