[Roles of posterior parietal cortex in stereopsis: characteristics of responses of axis-orientation-selective neurons in monkey caudal intraparietal area].

Patients with parietal lesions may fail to adjust the orientation of their hand to that of a target object, or may make errors in judging the orientation of a bar. This suggests that the parietal cortex has a function in the discrimination of the orientation of objects. In this study we investigated the responses of axis-orientation-selective neurons in caudal intraparietal (CIP) area to stereoscopic stimuli. Among the characteristics we investigated responses to the length and thickness of objects, sensitivity to binocular disparity, and position invariance in depth. Computer generated stereoscopic stimuli were presented to the monkey on a 70 inch screen. Most of the neurons responded better to long or narrow stimuli. All neurons which were orientation selective only in the frontal plane were not disparity sensitive. Most of the neurons which were orientation selective in the sagittal or horizontal plane were sensitive for binocular disparity. The majority of these neurons had wide receptive fields and their responses were position-invariant. These results suggest that the axis-orientation-selective neurons in CIP area encode the orientation of the longitudinal axis of objects in 3-dimensional space.