Online sensory feedback during active search improves tactile localization

Abstract

Natural motor behavior is usually refined by ongoing sensory input in closed feedback loops. Researchhas suggested that humans make systematic errors when localizing touch on the skin, and that perceptualbody representations underlying these behaviors are distorted. However, experimental procedures usuallyprevent participants from touching the target limb, interrupting the natural action-perception loop. It iscurrently unknown how such experimental strategies affect localization and systematic perceptualdistortions. Here, participants received a brief touch on their left forearm and, with closed eyes, searchedfor the target location by moving the right index finger across the left arm. Tactile search significantlyreduced the localization error present at touchdown of the searching finger on the target arm. Localizationimprovement was largely absent when a barrier above the target arm prevented online tactile feedbackof the target region. Vision of the arms while reaching to, and searching on, the skin, greatly reduced thelocalization error at touchdown, but tactile search further improved localization slightly. Thus, bothtactile and visual feedback help matching the positions of reaching and target limbs during localization.Yet, even if small, the unique improvement through tactile information confirms the importance oftarget-related, closed-loop tactile feedback for tactile localization.