Sensitivity to direction and orientation of random dot stereobars in the monkey visual cortex

We are able to judge the direction of movement and orientation of objects because they have contrast-defined edges. However, we are also able to perceive the orientation and direction of movement of stereobars made of random dot stereograms in the absence of contrast-defined edges. We recorded 207 disparity-sensitive cells from visual areas V1 and V2 of two Macaca mulatta monkeys while performing an attentive fixation task. Luminance defined bars and random-dot stereo-defined bars were used to assess direction and orientation selectivity of these cells. Orientation and direction preference for luminance bars and for stereobars showed a statistically significant relationship (r=0.83, P<0.01 for direction; r=0.63, P<0.01 for orientation). However, disparity-sensitive cells from these areas seem to be more sensitive to luminance than to stereobars regarding orientation and direction of movement. Similar results were obtained when the two areas were considered separately. Our results show that cells in areas V1 and V2 of the monkey visual cortex are able to detect the orientation and direction of movement of stereobars in a manner similar to those of luminance-defined bars. This finding is relevant because to detect the direction and orientation of stereobars a comparison between left and right eye inputs is required.