Rescaling Perceptual Hand Maps by Visual-tactile Recalibration

After concurrent visual and tactile stimuli have been presented repeatedly with a spatial offset, unisensory tactile stimuli, too, are perceived with a spatial bias towards the previously presented visual stimuli. This so-called visual-tactile ventriloquism aftereffect reflects crossmodal recalibration. As touch is intrinsically linked to body parts, we asked here whether recalibration occurs at the level of individual stimuli or at a higher, integrated, map-like level. We applied tactile stimuli to participants' hidden left hand and simultaneously presented visual stimuli with spatial offsets that, if integrated with the tactile stimuli, implied a larger hand. After recalibration, participants pointed to tactile-only stimuli and judged the distance between two tactile stimuli on the hand. The pattern of changes in tactile localization after recalibration was consistent with participants aiming at targets on an enlarged hand. This effect was evident also for new, tactile-only locations that had not been paired with visual stimuli during recalibration. In contrast, distance judgements were not consistently affected by recalibration. The generalization of recalibration to new, non-trained stimulus sites, but not across tasks and responses, suggests a link of low-level multisensory processing and map-like body representations that may, however, be purpose-specific and not organized as a general-purpose "body schema".