Somatosensory target information is used for reaching but not for saccadic eye movements

For any type of goal-directed hand and eye movement, it is important to determine the position of the target. Though many of these movements are directed toward visual targets, humans also perform movements to targets derived by somatosensory information only, such as proprioceptive (sensory signals about static limb position), kinesthetic (sensory signals about limb movement), and tactile signals (sensory signals about touch on skin). In this study we investigated how each of these types of somatosensory information influences goal-directed hand and eye movements. Furthermore, we examined whether somatosensory target information has a differential influence on isolated and combined eye-hand movements. Participants performed right-hand reaching, eye, or coordinated eye-hand movements to their left index or middle fingers in the absence of any visual information. We varied somatosensory target information by allowing proprioceptive, proprioceptive-kinesthetic, proprioceptive-tactile, or proprioceptive-kinesthetic-tactile information. Reach endpoint precision was poorest when the target was derived by proprioceptive information only but improved when two different types of input were available. In addition, reach endpoints in conditions with kinesthetic target information were systematically shifted toward the direction of movement, while static somatosensory information decayed over time and led to systematic undershoots of the reach target location. In contrast to the effect on reaches, somatosensory information did not influence gaze endpoint accuracy or precision. When performing coordinated eye-hand movements reach accuracy and gaze endpoint precision improved, suggesting a bidirectional use of efferent information. We conclude that somatosensory target information influence endpoint control differently for goal-directed hand and eye movements to unseen targets.NEW & NOTEWORTHY A systematic investigation of contributions of different somatosensory modalities (proprioception, kinesthesia, tactile) for goal-directed movements is missing. Here we demonstrate that while eye movements are not affected by different types of somatosensory information, reach precision improves when two different types of information are available. Moreover, reach accuracy and gaze precision to unseen somatosensory targets improve when performing coordinated eye-hand movements, suggesting bidirectional contributions of efferent information in reach and eye movement control.