Tactile Distance Adaptation Produces a Coherent Deformation of Tactile Space

Tactile distance illusions reveal systematic anisotropies in perceived spatial extent across the skin, such that distances oriented across the medio-lateral axis of the body are perceived as larger than those oriented along the proximo-distal axis. However, it remains unclear how these distortions are modified by the recent history of tactile stimulation. In the present study, participants judged the perceived distance between two touches on the dorsum of the hand across eight orientations, both before and after adaptation to a large tactile distance aligned with the medio-lateral axis. We applied the sinusoidal model of Fiori and Longo (2018) to characterise the geometric properties of tactile space and to quantify how they changed following adaptation. Adaptation produced a global reduction in perceived distance and a selective attenuation of anisotropy while preserving the orientation of maximal stretch. The aftereffects followed a sinusoidal tuning centred on the adapting orientation. Overall, our results indicate that somatosensory representations can adjust to recent stimulation without compromising their underlying spatial organisation, consistent with modulation at the level of population-based representations in somatosensory cortex.