Eye-hand coordination in on-line visuomotor adjustments

Abstract

When we perform a visually guided reaching action, the brain coordinates our hand and eye movements. Eye-hand coordination has been examined widely, but it remains unclear whether the hand and eye motor systems are coordinated during on-line visuomotor adjustments induced by a target jump during a reaching movement. As such quick motor responses are required when we interact with dynamic environments, eye and hand movements could be coordinated even during on-line motor control. Here, we examine the relationship between online hand adjustment and saccadic eye movement. In contrast to the well-known temporal order of eye and hand initiations where the hand follows the eyes, we found that on-line hand adjustment was initiated before the saccade onset. Despite this order reversal, a correlation between hand and saccade latencies was observed, suggesting that the hand motor system is not independent of eye control even when the hand response was induced before the saccade. Moreover, the latency of the hand adjustment with saccadic eye movement was significantly shorter than that with eye fixation. This hand latency modulation cannot be ascribed to any changes of visual or oculomotor reafferent information as the saccade was not yet initiated when the hand adjustment started. Taken together, the hand motor system would receive preparation signals rather than reafference signals of saccadic eye movements to provide quick manual adjustments of the goal-directed eye-hand movements.