Goal directed motor behavior and its adaptation following reversed tactile perception in man

When two adjacent fingers are crossed over each other and two tactile stimuli are touched to the two crossed fingertips, the two stimuli are perceived to be inverted in space. This phenomenon of tactile reversal was used in the present work to study the sensorimotor transformation occurring in goal directed motor behavior. When the subjects had to perform a movement toward a tactile stimulus (target) in tactile reversal conditions, the stimulus directed movements were performed wrongly, that is, away from the target. However, not all the subjects perceived a complete inversion of the stimuli; in this case, the target stimulus was perceived to be on the same side as its actual position, although with an error. In these conditions, the stimulus directed movements were performed correctly, that is, toward the target. These results show that the illusory spatial perception of the stimuli controls motor behavior on the basis of the amount of the perceptual error. Within the first hour of training, several compensatory responses occurred so as to produce correct motor performance. Despite this motor learning, reversed tactile perception remained reversed. Therefore, what subjects learned was the execution of the movements opposite to those necessary for reaching the target stimulus, without any change in perception. In the context of theories concerning the relationship between motor learning and perceptual adaptation, the present study shows that, with this experimental paradigm, motor learning during the first hour was mainly cognitive and did not have short-term effects upon perceptual processes.