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Adaptation aftereffects reveal that tactile distance is a basic somatosensory feature

Significance Visual adaptation aftereffects have been termed “the psychologist’s microelectrode” for the insight they provide into the neural bases of human vision. Less research has explored such aftereffects in touch. We exploit the distinction in vision between “low-level” aftereffects, showing location- and orientation-specificity characteristics of the early retinotopic cortex, and “high-level” aftereffects, showing high generality to these characteristics, and presumably arising from higher processing stages. We demonstrate that distance aftereffects in passive touch share numerous characteristics with low-level visual aftereffects, including orientation and region specificity, lack of transfer contralaterally or across palm and dorsum, and encoding in skin-based space. These results provide experimental evidence that tactile distance is a basic somatosensory feature, computed at relatively early somatosensory processing stages. The stage at which processing of tactile distance occurs is still debated. We addressed this issue by implementing an adaptation-aftereffect paradigm with passive touch. We demonstrated the presence of a strong aftereffect, induced by the simultaneous presentation of pairs of tactile stimuli. After adaptation to two different distances, one on each hand, participants systematically perceived a subsequent stimulus delivered to the hand adapted to the smaller distance as being larger. We further investigated the nature of the aftereffects, demonstrating that they are orientation- and skin-region–specific, occur even when just one hand is adapted, do not transfer either contralaterally or across the palm and dorsum, and are defined in a skin-centered, rather than an external, reference frame. These characteristics of tactile distance aftereffects are similar to those of low-level visual aftereffects, supporting the idea that distance perception arises at early stages of tactile processing.