Mental rotation of tactile stimuli

When subjects decide whether two visual stimuli presented in various orientations are identical or mirror-images, reaction time increases with the angular disparity between the stimuli. The interpretation of this well-known observation is that subjects mentally rotate images of the stimuli until they are in congruence, in order to solve the task. Here we review studies involving mental rotation of tactile stimuli. Mental rotation in tactile tasks is specifically associated with the requirement for mirror-image discrimination, as opposed to identity judgments. The key brain region mediating mental rotation of tactile stimuli seems to be the parietal cortex. Visual processing appears to facilitate task performance. We report an experiment from our laboratory addressing the nature of the reference frame for mental rotation of tactile stimuli. Our observations indicate that when the hand is directly in front of the body, with the head facing forward, the shortest reaction times for mirror-image discrimination of stimuli applied to the fingerpad are obtained when the longitudinal axis of the stimulus is in or parallel to the sagittal plane, even when this is perpendicular to the long axis of the finger. Thus, the reference frame for mental rotation of tactile stimuli is not purely hand-centered. This is consistent with other findings indicating variable assignment of reference frames for tactile perception.