Visuo-somatosensory reorganization in perceptual adaptation to reversed vision.

Humans can adapt to reversal of the visual field after long-term wear of reversing prism spectacles. Among various aspects of adaptation to reversed vision, adjustment of visually-guided behavior has been consistently found. On the other hand, there is relatively little quantitative evidence for 'perceptual adaptation', for example, restoration of perceptual harmony between the visual and tactile world. To elucidate perceptual adaptation to reversed vision, we conducted long-term experiments with continuous wear of reversing spectacles. Four human adult participants wore left-right reversing spectacles for 37 or 32days. Perceptual adaptation was examined by spatial left-right judgment tasks for visual, auditory, and somatosensory stimuli. In the visuo-motor (VM) and somato-visual (SV) tasks, correct responses disappeared completely at the beginning of prism wearing, but gradually restored, first in the VM task, and subsequently in the SV task. Moreover, the VM and SV tasks revealed aftereffects (incorrect responses) upon removal of the reversing prisms after the long adaptation period. In the auditory-motor (AM) task, responses were mostly correct irrespective of the reversed vision, but incorrect responses transiently appeared approximately when the adaptive change was first observed in the SV task. Moreover, starting from the period when these changes in the SV and AM tasks emerged, an adaptive sign of interhemispheric interaction was revealed by functional Magnetic Resonance Imaging. These results indicate that perceptual adaptation to reversed vision does occur, and that it proceeds to visuo-somatosensory reorganization, which seems to transiently accompany global cross-modal interactions.