Neural representation of three-dimensional features of manipulation objects with stereopsis

In the first part of this article, we review our neurophysiological studies of the hand-manipulation-related neurons in the anterior part of the later al bank of the intraparietal sulcus (area AIP). We describe the properties of visually responsive neurons in area AIP. Object-type visual-dominant neu rons responded to the Sight of objects and showed selectivity not only for simple geometrical shapes, but also for complex objects such as a knob-in-g roove and a plate-in-groove. Some of the object-type visual-dominant neuron s showed selectivity for the orientation of the longitudinal axis or the pl ane (surface) of a plate or a ring. In the second part of this article, we review our study of binocular visual neurons in the caudal part of the late ral bank of the intraparietal sulcus (c-IPS area), in particular, of axis-o rientation-selective (AOS) neurons and surface-orientation-selective SOS ne urons. AOS neurons preferred long and thin stimuli, were sensitive to binoc ular disparity, and tuned to the axis orientation in three-dimensional (3D) space. SOS neurons preferred broad and flat stimuli and were tuned to the surface orientation in depth. Some SOS neurons responded to a square in a r andom dot stereogram (RDS) with orientation tuning, suggesting that they en code surface orientation from a disparity gradient. Others responded to sol id figure stereograms with orientation disparity and/or width disparity. It was concluded that the c-IPS area is a higher center for stereopsis. which integrates various binocular disparity signals received from the V3 comple x and other prestriate areas to represent the neural code for 3D features. It may send projections to the AIP area and contribute to visual adjustment of the shape of the handgrip and/or hand orientation for manipulation and grasping. Neurons of the AIP area may also receive monocular cues of depth from the ventral visual pathway to discriminate the 3D shape of the object of manipulation.