Identifying neural sub-systems underlying human stereopsis

The psychophysical and oculomotor literatures have long proposed that stereoscopic vision is served by multiple underlying subsystems. The subsystems are usually construed in terms of dichotomies, e.g  patent vs qualitative, local vs global,  first-order vs second-order, transient vs sustained, absolute vs relative, etc.  Whether these multiple sub-systems are all independent is a matter of debate and moreover, there is very little known about their neural basis.  Here I will describe recent work in which we attempt to unify two of the more prominent dichotomies — one spatial — absolute vs relative disparity and the other temporal — transient vs sustained.  In a series of high-density EEG experiments using dynamic random dot stereograms that alternate between a flat plane and a stereo grating at 2 Hz, we find that odd harmonic components of the response reflect relative disparity extraction and that even harmonic components reflect absolute disparity extraction.   Moreover, the odd harmonics reflect a sustained temporal mechanism, while the even harmonics reflect a transient mechanism. Taken together our results indicate that relative disparities are processed by sustained mechanisms while absolute disparity processing is transient in nature. https://profiles.stanford.edu/anthony-norcia