DIRECTIONAL TUNING OF MOTION-SENSITIVE CELLS IN THE ANTERIOR SUPERIORTEMPORAL POLYSENSORY AREA OF THE MACAQUE

An investigation was made into the directional sensitivity of cells in the macaque anterior superior temporal polysensory region (STPa) to t he motion of objects. The cells studied were sensitive to the presence of motion but showed little or no selectivity for the form of the sti mulus. Directional tuning was not continuously distributed about all p ossible directions. The majority of cells were most responsive to moti on in a direction within 15-degrees of one of the three cartesian axes (up/down, left/right, towards/away). Tuning to direction varied in sh arpness. For most (34/37) cells the angular change in direction requir ed to reduce response to half maximal was between 45 and 70-degrees (f or 3/37 cells it was > 90-degrees). The estimates of the directionalit y (median I(d) = 0.97) of STPa cells was similar to that reported for posterior motion processing areas (the middle temporal area, MT, and t he medial superior temporal area, MST). The tuning for direction (shar pness, distribution and discrimination) of the motion-sensitive STPa c ells were found to be similar to the tuning for perspective view of ST Pa cells selective for static form of the head and body. On average th e STPa responses showed a 100- to 300-ms transient burst of activity f ollowed by a tonic discharge maintained at approximately 20% of the pe ak firing rate for the duration of stimulation. The responses of motio n-sensitive STPa cells occurred at an earlier latency (mean 91 ms) tha n responses of cells selective for static form (mean 119 ms), but the time course of responses of the two classes of cell were similar in ma ny other respects. The early response latency and directional selectiv ity indicate that motion sensitivity in STPa cells derives from the do rsal visual pathway via MT/MST. The similarity of tuning for direction and perspective view within STPa may facilitate the integration of mo tion and form processing within this high-level brain area.