Neural Responses to Texture Patterns in Area V1 of the Alert Monkey

Much of what our visual systems infers about a scene is based on cues derived from the visual texture of objects and surfaces in the scene. Areas of texture contrast are particularly salient and can automatically draw our attention. We recorded responses from cells in area V1 of the alert macaque monkey to texture stimuli in order to study the neurophysiology of texture segregation. A single oriented bar was placed in the center of a cell's classical receptive field (CRF) and we recorded the response to that center bar when it was alone against a blank background and when it was embedded in a texture of orthogonally oriented bars (orientation contrast texture) or identically oriented bars (uniform orientation texture). We found that the addition of the texture background suppressed the response to the center bar by an average of around 35%. In addition, for many cells there was a differential amount of suppression induced by the two texture backgrounds, such that the cell responded more strongly to the orientation contrast texture than to the uniform orientation texture. Such response properties correlate with the perceptual salience of the central bar. The same pattern of results was obtained when cells were tested with another noncontrast stimulus, a field of randomly oriented bars. The suppression from outside the CRF was shown to originate from areas on all sides of the CRF. A temporal analysis of the population responses to the center bar and the texture stimuli showed that both the general suppression and the orientation contrast effects are evident very early after stimulus onset. However, they both seem to take some small amount of time to develop, with the general suppression effect appearing about 7-10 msec after the onset of the population response and the orientation contrast effect appearing about 10-15 msec later. This short latency is consistent with the short presentation time sufficient in psychophysical studies of the popout effect for subjects to detect the presence of a target element differing in orientation from a field of distractors. The physiological response properties discussed here may underlie this perceptual ability.