Abstract
Ocular following eye movements are involuntarily responses to wide field motion, with a preferential bias to weight motion near the fovea (Quaia et al, 2012; Mukherjee et al, 2017). Previously, we found that saccades to peripheral apertures containing dot motion drive smooth eye movements immediately following saccade landing. These movements persisted even when the motion aperture disappeared in saccade flight, indicating that pre-saccadic motion selection initiates these responses. Here, we examined whether the smooth eye movements in our paradigm were more consistent with voluntary pursuit or with ocular following of motion at the saccade target. If they reflected ocular following, it would suggest that the weighting of motion in the visual field can be dynamically biased by pre-saccadic attention. While classical pursuit eye movements are voluntary and have a linear dependence on the target velocity, ocular following has a log-linear dependence. Thus we varied the velocity of motion in the target aperture to determine how it influenced post-saccadic following responses. As we increased the target velocity, we found the post-saccadic following velocity scaled more consistently with a log-linear dependence and had a low gain, consistent with ocular following. Analysis of secondary eye movements after saccades into the aperture also supported that the responses were involuntary. First, corrective saccades within 200ms of the primary saccade into the aperture were directed towards the aperture’s center, rather than along the target motion. Second, on those trials where the primary saccade deviated along the axis of target motion, following responses were smaller or opposite of the target motion, reflecting eye movements back to the aperture center rather than pursuit. Taken together, these findings support that the smooth movements we observed were consistent with involuntary ocular following. Moreover, pre-saccadic attention to motion information can bias the spatial weighting of motion integration that drives these responses.