Study of the Influence of Visuo-Haptic Feedback on Prosthetic Embodiment

When improving an upper-limb prosthetic system, choosing whether to prioritise visual design or haptic performance becomes crucial and offers valuable insights for advancing prosthesis development. This paper investigates the influence of multisensory feedback on prosthetic embodiment, focusing on key components of embodiment, including ownership, multisensory, and agency, through two Virtual Reality (VR) experiments. Our first study involved 24 participants without limb loss in a target-reaching task using different visual renderings (glove, realistic, prosthetic hands) and haptic feedback modalities (none, vibrotactile, pressure, combined). Results showed that visual appearance was a powerful determinant across all components. Realistic hands produced the highest embodiment scores, whereas the prosthetic hand representation significantly degraded them. Haptic feedback substantially affected ownership and multisensory scores; pressure feedback improved ownership compared to no feedback, and all haptic conditions elevated multisensory scores. A subsequent experiment with 12 new participants explored the effect of haptic feedback location (wrist, forearm, upper arm, contralateral forearm). This experiment found no significant performance differences among locations, though co-located feedback was preferred, where the visual feedback in VR appeared at the same spatial position as the perceived tactile contact. Finally, a pilot study with a prosthetic user provided preliminary support for the relevance of realistic visual appearance and multimodal haptic feedback. Overall, results suggest that visual realism and haptic feedback support different dimensions of prosthetic embodiment, with visual realism mainly enhancing ownership and haptic feedback strengthening multisensory. Importantly, concurrent vibrotactile-pressure feedback emerged as a promising and well-accepted solution, providing richer interaction cues without compromising embodiment.