Coding of egocentric distance in the macaque ventral intraparietal area.

The encoding of three-dimensional visual information is of important in everyday life. Eye-movements challenge this spatial encoding: they shift the image of the outside world across the retina. In the macaque ventral intraparietal area (VIP), many neurons encode visual information irrespective of horizontal and vertical eye position. Does this gaze invariance of spatial encoding extend to egocentric distances? Such invariance would correspond to a shift of disparity-tuning curves by vergence angle. Here, monkeys fixated one of three distances (vergence), while a visual stimulus was shown at one of seven distances (disparity). Most neurons' activity was modulated independently by both disparity and eye vergence, and we did not observe shifts of disparity-tuning curves as expected from encoding egocentric distances at a single-cell level. By using population activity, however, we were able to decode egocentric distance. Our results provide further strong evidence for a role of area VIP in 3D space encoding.