In grasping the orientation of an object plays a significant role, as it influences both the a??grasping component" as well as the a??transport component " (Jeannerod, 1981, 1984). Therefore investigating the effects of changing object orientation during the movement might provide further insights to the visuomotor control of grasping. To this end, 20 participants grasped a vertically aligned bar (length = 50 mm, width = 20 mm) with a precision grip. Participants could freely choose a comfortable grasp axis. In 20 % of the trials the orientation of the bar was changed during the movement (by 20?° or 90?°). The change occurred after index finger or thumb moved 2 cm away from the starting position, or after 2/3 of the movement distance was covered. In the remaining 80 % of the trials the orientation of the bar was not changed. When the orientation of the bar was not changed, participants grasped it along its length. When the bar was rotated by 20?°, participants also changed their hand orientation, and kept grasping the bar along its length. Also, in both conditions the maximum grip aperture was scaled to the length of the bar. However, when the bar was rotated by 90?° participants grasped the bar along its width, scaling the MGA to the width of the bar, but not altering the orientation of their hand. Interestingly these adaptation processes did not depend on the moment of perturbation. Our results indicate that the visuomotor system is able to process information about object orientation flexibly at different stages of the movement, depending on external demands (orientation of the object) and internal factors (comfort of the grip).
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