Contribution of retinal motion toward the impulse control of target-directed aiming

Contemporary models of sensorimotor control contend that visually-regulated movement adjustments may unfold early during a target-directed limb movement courtesy of an impulse control process that makes use of anticipatory forward models. To-date, evidence surrounding impulse control involves adjustments to a purported misperception in limb velocity following the unexpected onset of a moving background. That is, the limb is perceived to move faster and undershoots more whenever there is an incongruent moving background, and vice-versa. However, it can be argued that this particular behaviour may alternatively manifest from an independent oculo-manual-following response. The present study aimed to deconstruct these proposals, and with it, the processes that underlie impulse control. Participants had to rapidly reach upward to land their index finger accurately on a target. On 33% of trials, the background, over which the movement was made, moved in either the upward, downward, rightward, or leftward directions. Displacements within the primary and perpendicular directions of the movement showed spatial trajectories that were consistent with the directions of the moving backgrounds. This behaviour was most prevalent in measurements taken at the movements’ peak negative acceleration and endpoints. Moreover, the analysis of standardized displacements in the moving background conditions indicated no significant differences in the extent of the movements toward each of the moving backgrounds. These findings indicate that movement adjustments can manifest from an oculo-manual-following response rather than a misperception in limb velocity. We suggest that the anticipatory forward model that comprises impulse control may incorporate features of the environment that surround the vicinity of the limb