Combined contribution of tactile and proprioceptive feedback to hand movement perception.

UNLABELLED: Here we investigated how the tactile modality is used along with muscle proprioception in hand movement perception, whether these two sensory inputs are centrally integrated and whether they work complementarily or concurrently. The illusory right hand rotations induced in eleven volunteers by a textured disk scrolling under their hand in two directions at three velocities and/or by mechanical vibration applied to their wrist muscles at three frequencies were compared. The kinesthetic illusions were copied by the subjects on-line with their left hand.
RESULTS: 1) in all the subjects, tactile stimulation alone induced an illusory hand rotation in the opposite direction to that of the disk, and the velocity of the illusion increased non-linearly with the disk velocity: the highest gain (the illusion velocity to disk velocity ratio) occurred at the slowest disk rotation; 2) adding a consistent proprioceptive stimulus increased the perceptual effects, whereas adding a conflicting proprioceptive stimulus of increasing frequency gradually decreased the tactile illusions and reversed their initial direction; 3) under both consistent and conflicting conditions, only strong proprioceptive stimulation significantly affected the gain of the resulting illusions, whereas the largest gain always occurred at low tactile stimulation levels when the illusory movements were in the same direction as the tactile-induced illusion. Tactile information may equal or even override muscle proprioceptive information in the perception of relatively small, slow hand movements. These two somatosensory inputs may be integrated complementarily, depending on their respective relevance to the task of accurately perceiving one's own hand movements.