Abstract
This study investigates the effects of body posture and the direction of acceleration due to gravity on the variance of response distances using a somatosensory system. The participants were blindfolded using eye masks and verbally instructed to alternately identify the initial point as well as spot a point along the semicircumference of a 15- or 25-cm radius with its origin at the distal side using their right index finger. The participants performed this task in five different postures (i.e., standing, supine, right decubitus, left decubitus, and prone). As a result, the response distances tended to be shorter than the target distance, especially for postures other than standing. A moderate positive correlation was observed between the response distance and each velocity in the radial direction and the peak pointing velocity. In postures other than standing, unintentional changes in motion velocity because of arm movement suppression or acceleration were caused due to gravity. This affected the distance perception derived from arm motion velocity.
