Effect of visuomotor learning in arm reaching movement on the visual boundary associated with the direction of target motion

This paper examines whether motor learning affects sensory function, in particular, visual perception in the context of a visuomotor learning paradigm involving arm reaching movements. An experimental task of arm reaching movements requires somatosensory and visual information to improve their performance in trials. The somatosensory perception, limb positional perception, has been reported to change during the motor learning. Then, we wonder whether the visual perception does not change even though it is utilized as the same as somatosensory perception during the reaching movement. To answer this question, we designed an experimental procedure that included visual tests before and after visuomotor learning. Among many characteristics of the visual perception, the perception of movement direction of a visual target, a cursor, was focused. In the normal motor learning task, participants repeat reaching movements to visual targets without seeing the actual movement of the arm: Instead, the cursor is presented to denote the current hand position. However, in our experiments, cursor was intentionally displayed in some deviations, more to the left or the right of the actual hand position. In the visual tests, the participants observed a cursor moving outward along the body midline, but deviating slightly to the left or the right. They were asked to indicate which side (left or right) the cursor was deviated to. From the participants' responses, we determined the visual perceptual direction that separated the left and the right, which we call here the visual boundary. The experiments with eight participants revealed that the visual boundary shifted in a direction opposite to that of the cursor display deviation, implying that the motor learning might affect visual perception.