Tactile mislocalisation of the digits arises from higher-level representation of individual digits as complete 3D units

Recent research has shown systematic patterns of mislocalisations and confusions between digits. These distortions appear highly stereotyped, and consistent across individuals. The present study addressed whether such mislocalisations arise from early somatosensory maps or from higher-level body representations. We obtained confusion matrices showing pattern of mislocalisation between toes and fingers on the glabrous and hairy surface of the foot and hand. As the two skin surfaces of the hands and feet have distinct representations in somatosensory cortex, an effect arising from early somtotopic maps may show distinct patterns on each skin surface. In contrast, if the effect arises from higher-level body representations which represent the digits as complete, volumetric units, similar patterns should be apparent regardless of which side of the digit is touched. Our results clearly replicated the distinct pattern of mislocalisations on the glabrous skin of the fingers and toes. Critically, these effects were highly similar on the hairy skin. Despite the pattern of mislocalisations being highly stereotyped across participants, there were consistent individual differences in task performance across the two skin surfaces. These results suggest that mislocalisations occur at the level of complete toes, rather than individual skin surfaces, consistent with their resulting from higherlevel body representations.