Online Sensory Feedback During Active Search Improves Tactile Localization

Abstract

Natural motor behavior is usually refined by ongoing sensory input in closed feedback loops. Research has suggested that humans make systematic errors when localizing touch on the skin, and that perceptual body representations underlying these behaviors are distorted. However, experimental procedures usually prevent participants from touching the target limb, interrupting the natural action-perception loop. It is currently unknown how such experimental strategies affect localization and systematic perceptual distortions. Here, participants received a brief touch on their left forearm and, with closed eyes, searched for the target location by moving the right index finger across the left arm. Tactile search significantly reduced the localization error present at touchdown of the searching finger on the target arm. Localization improvement was largely absent when a barrier above the target arm prevented online tactile feedback of the target region. Vision of the arms while reaching to, and searching on, the skin, greatly reduced the localization error at touchdown, but tactile search further improved localization slightly. Thus, both tactile 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 of target-related, closed-loop tactile feedback for tactile localization