Reaching movement accuracy is mainly determined by visual online control

Here we demonstrate that the accuracy of reaching a target is affected by neither the representation of the target location nor the visual feedback provided up to 250ms before movement completion. Observers performed reach-to-point movements for a real cylinder positioned at variable locations. We manipulated the visual information (monocular/binocular) provided in two contiguous segments. Main segment: trajectory from the movement start up to 250 ms before movement completion. Final segment: trajectory during the final 250 ms to reach the target. The accuracy of the end position (z-depth) of the reaching movement was measured. We found reliable effects of visual information sampled during the final segment, but not during the main segment. Reaching was accurate if disparity information was provided throughout the whole movement or only in the last 250 ms segment. Overshooting of 1 cm was found when disparity information was absent during the whole movement or in the last 250 ms segment. The latter is surprising, as the target appeared binocular for most of the movement duration allowing for ample time to plan the movement-end. Thus, accuracy in reaching performance can be explained by nulling the relative disparity between the finger and the target. Our results indicate the importance of the online component of visual-motor control.