Involvement of cerebellar vermis in the perception of depth from motion explored with Transcranial Magnetic Stimulation

Current models suggest that the unambiguous perception of depth from motion parallax (MP) relies on the integration of retinal image motion with a pursuit eye movement signal, which previous work has suggested may be generated by the frontal eye fields (FEF). In the present study, we used Transcranial Magnetic Stimulation (TMS) to explore a possible role of the Cerebellar vermis (CV) in these computations. Both physical lesions to and TMS of the CV, but not the cerebellar hemispheres, have been found to disrupt motion perception and produce smooth pursuit deficits. However, a possible role of the CV in the computation of depth from MP has not been explored. In the present study, we used TMS to investigate this possibility. Triple-pulse (33 hz) TMS was applied to mid-line CV (1 cm below the inion) at the time of visual stimulus onset (0 msec ISI) during three tasks: i) pursuit, ii) motion perception, and iii) MP depth perception. The pursuit task was a step-ramp. Psychophysical tasks required the observer to report perceived depth or perceived motion direction (2AFC) of a computer-generated random-dot stimulus making a single translation, leftward or rightward, of duration (t). Between trials, t varied in two interleaved staircases, one for each direction of stimulus translation. Average performance from 35 participants indicates that TMS of CV produced an overall decrease in pursuit latency (13 msec for leftward and 11 msec for rightward translation). Similarly, for depth perception, TMS produced a decrease in pursuit latency in both directions (25 msec for leftward and 18 msec for rightward translation). TMS produced no change in motion perception latency for either direction of stimulus translation. These results suggest that cerebellar vermis may play a role in the integration of the pursuit signal needed for the unambiguous perception of depth from MP.