Dynamic tuning of tactile localization to body posture

Abstract

Localizing touch in space is essential for goal-directed action. Because body posture changes, the brain must transform tactile coordinates from an initial skin-based representation to external space by integrating information about current posture. This process, referred to as tactile remapping, generally results in accurate localization, but accuracy drops when skin-based and external spatial representations of touch are conflicting, e.g., after crossing the limbs. Importantly, frequent experience of such postures can improve localization. This suggests that remapping may not only integrate current sensory input but also prior experience. Here, we demonstrate that this can result in rapid changes in localization performance over the course of few trials. We obtained an implicit measure of tactile localization by studying the perceived temporal order of two touches, one on each hand. Crucially, we varied the number of consecutive trials during which participants held their arms crossed or uncrossed. As expected, accuracy dropped immediately after the arms had been crossed. Importantly, this was followed by a progressive recovery if posture was maintained, despite the absence of performance feedback. Strikingly, a significant improvement was already evident in the localization of the second pair of touches. This rapid improvement required preceding touch in the same posture and did not occur merely as a function of time. Moreover, even touches that were not task relevant led to improved localization of subsequent touch. Our findings show that touches are mapped from skin to external space as a function of recent tactile experience.