Analysis of optic flow in the monkey parietal area 7a.

Environmentally relevant stimuli were used to examine the selectivity of area 7a neurons to optic flow using moving, flickering dots. Monkeys performed a psychophysical task requiring them to detect changes in translation, rotational and radially structured optic flow fields consisting of collections of moving dots which are free of form cues. The neurons in area 7a were selectively responsive to all the different types of moving stimuli. Two types of tuning for motion selectivity were found. Some neurons were tuned to distinguish a particular direction of optic flow (e.g. radial expansion versus radial compression), while others were tuned to distinguish between different classes of optic flow (e.g. radial motion versus planar rotation). The latter tuning was unlike that reported for area MST by others and may represent a novel representation of optic flow. The response of these neurons to translating bars was compared to that of optic flow fields. There appeared to be no similarity in the tuning to the two types of motion. Furthermore, there does not appear to be an identity between the neurons that could be classified as opponent vector and those selective for radial optic flow. Area 7a is involved in the further analysis of optic flow beyond the cortical areas MT and MST and provides a novel representation of motion. These results are consistent with the neurons in area 7a utilizing motion for the construction of a spatial representation of extra-personal space.