Visuomotor Map Determines How Visually Guided Reaching Movements are Corrected Within and Across Trials

Abstract

When a visually guided reaching movement is unexpectedly perturbed, it is implicitly corrected in two ways: immediately after the perturbation by feedback control (online correction) and in the next movement by adjusting feedforward motor commands (offline correction or motor adaptation). Although recent studies have revealed a close relationship between feedback and feedforward controls, the nature of this relationship is not yet fully understood. Here, we show that both implicit online and offline movement corrections utilize the same visuomotor map for feedforward movement control that transforms the spatial location of visual objects into appropriate motor commands. First, we artificially distorted the visuomotor map by applying opposite visual rotations to the cursor representing the hand position while human participants reached for two different targets. This procedure implicitly altered the visuomotor map so that changes in the movement direction to the target location were more insensitive or more sensitive. Then, we examined how such visuomotor map distortion influenced online movement correction by suddenly changing the target location. The magnitude of online movement correction was altered according to the shape of the visuomotor map. We also examined offline movement correction; the aftereffect induced by visual rotation in the previous trial was modulated according to the shape of the visuomotor map. These results highlighted the importance of the visuomotor map as a foundation for implicit motor control mechanisms and the intimate relationship between feedforward control, feedback control, and motor adaptation.

Significance statement: Feedforward control of reaching movements relies on a visuomotor map that translates motor planning, based on the target’s location, into an appropriate movement. However, movements could be unexpectedly perturbed, indicating that additional mechanisms for movement corrections are necessary. We hypothesize that the visuomotor map provides the motor system with the knowledge of how the movement should be corrected during the movement (feedback control) and in the next movement (motor adaptation). We demonstrate that distorting the visuomotor map, by a visuomotor adaptation paradigm, alters the magnitudes of both movement corrections according to the shape of the distortion. Our results show the significance of visuomotor map and intimate link between feedforward control, feedback control, and motor adaptation through a visuomotor map.