Abstract
It has been recently found that the manual following response (MFR), which is shortly induced by applying a surrounding visual motion during reaching, is modulated by a spatial relationship between gaze and reaching target locations (Abekawa & Gomi 2006 Society for Neurosci.). On the other hand, change in the spatial relationship between reaching target and visual motion locations appeared not to affect the MFR. However, it has not yet been examined whether or not the hand position relative to the motion stimulus affects the MFR. To investigate this aspect, we conducted an experiment in which the location of visual motion stimulus (longitudinal grating-pattern motion in 120 x 13 cm) was changed along the reaching path from proximal to distal positions (proximal, middle, and distal). Each stimulus started to move transversally at different hand positions (proximal, middle, and distal) during arm-extension reaching movements. The distal stimulus with the middle hand position induced the greatest MFR among all nine conditions, and that stimulus with the proximal and distal hand positions also greatly induced the MFR. The middle stimulus with the proximal and middle hand positions also induced the MFR clearly, but that with the distal hand position did not induce the MFR significantly. The proximal stimulus with any hand positions did not induce the MFR while the same stimulus induced the MFR during arm-flexion reaching movements. These MFR variations, therefore, could not be explained only by changes in the stimulus location on the retina and in the relationships between the gaze and reaching target locations. The MFR variations observed in the experiment suggest that the MFR is affected not only by the hand position but also by the hand movement direction relative to the stimulus location.