Neural mechanisms underlying the computation of depth from motion parallax - Vision is an active process, and we frequently move our eyes to track targets of interest as we ourselves move. While useful for maintaining the fovea on a target, these 'pursuit' eye movements add global patterns of motion to the retinal image. Thus, to compute the motion or depth of objects in the world, our visual system must account for the image motion added by eye rotations. The standard view is that signals other than retinal image motion, such as efference copy of pursuit command signals, must be used to compensate for eye rotations. In this view, one would subtract off the visual motion resulting from eye rotation such that the remainder conveys information about motion of objects in the world. The present project assesses an alternative view, that the visual system uses this internal eye movement signal as a proxy for information about self-motion in relation to the point of fixation. More specifically, for Aim 1, we propose to use non-invasive brain stimulation (TMS) to investigate whether extra-retinal signals generated by the frontal eye fields (FEF) are necessary for the perception of depth from motion parallax. If TMS disruption of FEF processing is deleterious to the perception of depth from motion parallax, this would indicate that FEF is the source of the internal pursuit signal and is therefore part of the neural processing mechanism for the perception of motion. Alternatively, if TMS disruption of FEF does not affect the perception of depth from motion, this would suggest that the visual system instead relies on an earlier sensory foveal motion signal, the specific signal that elicits or drives the pursuit initiation signal, in the neural computation of depth from motion parallax. Aim 2 proposes to use TMS to assess the role of two additional brain areas in the computation of depth from motion parallax: visual area Middle Temporal (MT) and the Cerebellar Vermis. Both of these areas have been implicated in the perception of object motion, and are uniquely positioned to integrate the motion-related and extra-retinal pursuit signals needed to compute depth from motion parallax. However, their role in depth perception, and in particular in the computation of depth from motion parallax, remains unclear. If TMS of either area disrupts depth judgments, this would suggest a role in processing the extra-retinal pursuit signal generated by the FEF. Our previous work has made important advances in understanding the theoretical, psychophysical, and neurophysiological mechanisms of computing depth from motion parallax. The proposed project extends these investigations by directly assessing the role of the FEF, MT, and vermis in the computation of depth from motion parallax.
