Body image as a visuomotor transformation device revealed in adaptation to reversed vision

People adapt with remarkable flexibility to reversal of the visual field caused by prism spectacles(1,2). With sufficient time, this adaptation restores visually guided behaviour and perceptual harmony between the visible and tactile worlds(1-3). Although it has been suggested that seeing one's own body is crucial for adaptation(1,2), the underlying mechanisms are unclear. Here we show that a new representation of visuomotor mapping with respect to the hands emerges in a month during adaptation to reversed vision. The subjects become bi-perceptual(3-5), or able to use both new and old representations. In a visual task designed to assess the new hand representation, subjects identified visually presented hands as left or right by matching the picture to the representation of their own hands. Functional magnetic resonance imaging showed brain activity in the left posterior frontal cortex (Broca's area) that was unique to the new hand representations of both hands, together with activation in the intraparietal sulcus and prefrontal cortex. The emergence of the new hand representation coincided with the adaptation of perceived location of visible objects in space. These results suggest that the hand representation operates as a visuomotor transformation device that provides an arm-centred frame of reference(6) for space perception.