NEURAL CODING OF 3D FEATURES OF OBJECTS FOR HAND ACTION IN THE PARIETAL CORTEX OF THE MONKEY

In our previous studies of hand manipulation task-related neurons, we found many neurons of the parietal association cortex which responded to the sight of three-dimensional (3D) objects. Most of the task-relat ed neurons in the AIP area (the lateral bank of the anterior intrapari etal sulcus) were visually responsive and half of them responded to ob jects for manipulation. Most of these neurons were selective for the 3 D features of the objects. More recently, we have found binocular visu al neurons in the lateral bank of the caudal intraparietal sulcus (c-I PS area) that preferentially respond to a luminous bar or plate at a p articular orientation in space. We studied the responses of axis-orien tation selective (AOS) neurons and surface-orientation selective (SOS) neurons in this area with stimuli presented on a 3D computer graphics display. The AOS neurons showed a stronger response to elongated stim uli and showed tuning to the orientation of the longitudinal axis. Man y of them preferred a tilted stimulus in depth and appeared to be sens itive to orientation disparity and/or width disparity. The SOS neurons showed a stronger response to a fat than to an elongated stimulus and showed tuning to the 3D orientation of the surface. Their responses i ncreased with the width or length of the stimulus. A considerable numb er of SOS neurons responded to a square in a random dot stereogram and were tuned to orientation in depth, suggesting their sensitivity to t he gradient of disparity We also found several SOS neurons that respon ded to a square with tilted or slanted contours, suggesting their sens itivity to orientation disparity and/or width disparity Area c-IPS is likely to send visual signals of the 3D features of an object to area AIP for the visual guidance of hand actions.