Adaptation of the precision grip orientation to a visual-haptic mismatch.

Using a sequential-exposure approach, we examined sensorimotor adaptation of precision grip orientation to a visuo-haptic mismatch. Subjects (n = 41) were asked to grasp with thumb and index finger mirror-viewed objects. They could not see their hand due to the mirror, but they could feel an object located behind the mirror in the same place as the viewed object. When a -15 degrees orientation mismatch between viewed and felt object was introduced, subjects adapted to it by gradually modifying the orientation of their finger opposition axis. When the visuo-haptic mismatch further changed to -30 degrees or to +15 degrees , subjects continued to perform according to their pre-established adaptive state, and gradually modified it until it became adequate for the new mismatch. This outcome supports the existence of a continuously acting mechanism for grasping adaptation, similar to that previously described for pointing and tracking adaptation. Precision grip adaptation generalized to unpracticed object orientations, which suggests that adaptation was based on a sensorimotor recalibration rather than the learning of specific stimulus-response pairs. Transfer to pointing movements was found only when similarity to the grasp adaptation task was high.