Importance of somatosensory input for spatial orientation in supine subjects: evaluated by pointing arm movements...

Goal-directed movements are secured by sensory interactions among visual, vestibular and somatosensory information. Reliable inputs from the visual system have been known, and the contribution of otolithic information demonstrated most clearly by evidence that target-pointing arm movements shifted downward in astronauts with eyes closed under space microgravity (Watt 1997), whereas the direction of shift was the opposite in subjects under centrifuge hypergravity (Bock et al. 1996). Somatosensory contribution has been also supported by many reports. In the present study, we attempted to evaluate the otolithic contribution to spatial orientation by arm-pointing deviation in supine subjects exposed to Z-axis linear acceleration in darkness.