Augmenting natural skin stretch during active finger motion reshapes hand proprioception.

There is strong evidence that skin stretch at the joint contributes to proprioception, the perceptual representation of body position and motion. Previous studies on fingers and hand dorsum focused on illusory movement elicited by skin-stretch stimuli when no actual motion was performed, often combined with local anesthesia and mostly delivered qualitatively, leaving unclear how controlled, augmented skin deformation influences proprioception during active movement. Here, we addressed this question by applying precisely scaled skin-stretch stimuli across the proximal interphalangeal (PIP) joint of the index finger, amplifying naturally occurring deformations during finger flexion. Participants performed an active hand position-matching task with their bare hand and while wearing a custom, non-invasive tactile device capable of controlled skin-stretch stimulation. While no significant differences were observed between the bare hand and the device-deactivated condition, augmenting natural skin stretch consistently shifted perceived finger posture toward more extended configurations. This finding demonstrates that cutaneous deformation can systematically reshape proprioceptive estimates even when muscle spindles and efferent signals are engaged, revealing a continuous integration of tactile and musculoskeletal cues in kinesthetic perception. These results advance our understanding of skin-stretch contribution to proprioceptive processing in active tasks, with implications for haptics-based human-machine interaction and virtual reality applications.