Responses of striate neurons to line textures were investigated in anesthetized and paralyzed adult cats. Light bars centered over the excitatory receptive field (RF) were presented with different texture surrounds composed of many similar bars. In two test series, responses of 169 neurons to textures with orientation contrast (surrounding bars orthogonal to the center bar) or motion contrast (surrounding bars moving opposite to the center bar) were compared to the responses to the corresponding uniform texture conditions (all lines parallel, coherent motion) and to the center bar alone. In the majority of neurons center bar responses were suppressed by the texture surrounds. Two main effects were found. Some neurons were generally suppressed by either texture surround. Other neurons were less suppressed by texture displaying orientation or motion (i.e. feature) contrast than by the respective uniform texture, so that their responses to orientation or motion contrast appeared to be relatively enhanced (preference for feature contrast). General suppression was obtained in 33% of neurons tested for orientation and in 19% of neurons tested for motion. Preference for orientation or motion contrast was obtained in 22% and 34% of the neurons, respectively, and was also seen in the mean response of the population. One hundred nineteen neurons were studied in both orientation and motion tests. General suppression was correlated across the orientation and motion dimension, but not preference for feature contrast. We also distinguished modulatory effects from end-zones and flanks using butterfly-configured texture patterns. Both regions contributed to the generally suppressive effects. Preference for orientation or motion contrast was not generated from either end-zones or flanks exclusively. Neurons with preference for feature contrast may form the physiological basis of the perceptual saliency of pop-out elements in line textures. If so, pop-out of motion and pop-out of orientation would be encoded in different pools of neurons at the level of striate cortex.

We studied the effects of contextual modulation in area V1 of anesthetized macaque monkeys. In 146 cells, responses to a single line over the center of the receptive field were compared with those to full texture patterns in which the center line was surrounded by similar lines at either the same orientation (uniform texture) or the orthogonal orientation (orientation contrast). On average, the responses to single lines were reduced by 42% when texture was presented in the surround. Uniform textures often produced stronger suppression (7% more, on average) so that lines with orientation contrast on average evoked larger responses than lines in uniform texture fields. This difference is correlated with perceptual differences between such stimuli, suggesting that physiological mechanisms contributing to the saliency (“popout”) of textural stimuli operate, at least to some degree, even under anesthesia. Significant response modulation by the texture surround was seen in 112 cells (77%). Fifty-three cells (36%) responded differently to the two texture patterns; response preferences for orientation contrast (35 cells; 24%) were seen more often than preferences for uniform textures (18 cells; 12%). The remaining 59 cells (40%) were similarly suppressed by both texture surrounds. Detailed analysis of texture modulation revealed two major components of surround effects: (1) fast nonspecific (“general”) suppression that occurred at about the same latency as excitatory responses and was found in all layers of striate cortex; and (2) differential response modulation that began about 60–70 ms after stimulus onset (about 15–20 ms after the onset of the excitatory response) and was less homogeneously distributed over cortical layers.