RESPONSES OF MACAQUE STS NEURONS TO OPTIC FLOW COMPONENTS - A COMPARISON OF AREAS MT AND MST

1. We recorded and tested quantitatively 65 middle temporal (MT) and 8 2 middle superior temporal (MST) cells in paralyzed and anesthetized m onkeys. 2. Responses to the three elementary optic flow components (EF Cs)-rotation, deformation, and expansion/contraction-and to translatio n (in the display) were compared after optimization of stimulus direct ion, speed, size, and position. As a control responses to flicker were measured. 3. Response windows were adapted in correspondence with our finding that latencies of MT and MST cells decrease with increasing s peed for all types of motion. 4. There was a response continuum in MT as well as in MST cells. Compared with translation, MST cells responde d significantly more to rotation but less to flicker than MT cells. MS T cells were significantly more direction selective for expansion/cont raction than MT cells. 5. MST cells generally responded to fewer motio n types than MT cells. 6. Position invariance of EFC direction selecti vity was tested over a region of the visual field centered on the tran slation receptive field(RF). Direction selectivity for an EFC was not position invariant in MT cells but it was invariant in 40% of the MST cells tested. These cells were considered EFC selective. 7. Most EFC-s elective MST cells were selective for a single EFC, possibly combined with translation Few of them were selective for deformation. 8. EFC se lectivity was also speed invariant and EFC-selective MST cells usually had RFs summating inputs over wide portions of the visual field. 9. E FC-selective MST cells with similar selectivities were clustered.