Tactile distance illusions reflect a coherent stretch of tactile space

Illusions of the perception of distance between two touches on the skin have been described since the classic work of Weber in the 19th century. The perceptual mechanisms underlying such spatial distortions, however, remain poorly understood. One potential interpretation is that the representational space of touch is related to the true structure of the skin by a geometrically simple stretch. If distortions of tactile distance perception reflect a simple stretch of tactile space, perceived distance should vary predictably as a function of the orientation of the stimulus on the skin, showing a sinusoidal pattern. Here, we tested this prediction by obtained judgments of perceived tactile distance for pairs of touches aligned with eight orientations on the skin. Across four experiments, the results were highly consistent with this prediction, showing no apparent deviation from a model of simple stretch of tactile space. Similar results were apparent on both the dorsum and palm of the hand, as well as the forehead. These results show that spatial distortions of touch are well characterized by a geometrically simple stretch of tactile space.