Abstract
The unambiguous perception of depth from motion parallax (MP) relies on the neural integration of retinal image motion with a pursuit eye movement signal. Transcranial Magnetic Stimulation (TMS) was used to investigate underlying neural mechanisms, particularly the slow eye-movement region of the Frontal Eye Fields’ (FEFsem) role in generating the pursuit signal necessary to disambiguate MP. If TMS of FEFsem increases pursuit latency for contralateral movements, and if FEFsem provides the necessary pursuit signal for perception of depth from MP, then TMS of FEFsem should increase the presentation duration needed for depth from a MP stimulus translating in the contralateral direction. FEF was localized to individual anatomy (T1-weighted MRI) and functionally refined as the region of FEF that, when stimulated, produced an increase in pursuit latency. Following localization, single-pulse TMS was applied to right FEFsem 50 msec after stimulus motion onset during: i) pursuit, ii) motion perception, and iii) MP depth perception tasks. In the MP task, observers reported perceived depth phase (2AFC) upon viewing a computer-generated random-dot MP stimulus making a single translation of duration (t). Between trials, t varied in two interleaved staircases, one for each direction of stimulus translation. Stimuli were presented on a 120 Hz CRT and eye position was monitored with remote optics eye-tracking. Overall, TMS produced an average 25 msec increase in pursuit latency in the contralateral direction, but not in the ipsilateral direction. As hypothesized, TMS also produced direction and task-specific effects on performance; there was an average 25 msec increase in the MP presentation duration required for depth perception with stimulus translations in the contralateral direction. The temporal magnitude of the pursuit and MP effects were significantly correlated. These results indicate that FEFsem has a role in the production of the pursuit signal needed for the unambiguous perception of depth from MP.
Acknowledgement: NIGMS P30 GM114748