This research explores the frontier of human body augmentation through supernumerary robotic limbs—artificially designed extra appendages that extend beyond our natural physical capabilities. The core challenge addressed is achieving “cognitive transparency,” enabling users to perceive and control additional robotic limbs as naturally as their own body parts, without cognitive overload. The study investigates the phenomenon of “embodiment”—the perceptual shift where external objects become integrated into one’s body schema. While previous research has extensively examined body augmentation through replacement or extension of existing limbs, this work specifically focuses on the underexplored area of functional enhancement through the addition of extra body parts.
Technical Implementation
We developed a supernumerary robotic limb system operating in virtual reality environments. The system enables users to control additional robotic arms while measuring their subjective experience of embodiment and changes in peripersonal space perception—the area immediately surrounding the body where we can reach and interact with objects.
Key Research Findings
Novel “Supernumerary Limb Sensation”: Post-training subjective evaluations revealed that participants successfully embodied the robotic arms, leading us to propose a new category of embodiment called “supernumerary limb sensation.”
Spatial Perception Changes: We discovered a positive correlation between visuotactile integration changes around the supernumerary limbs (peripersonal space alterations) and participants’ subjective experience of having additional arms. This represents the first documentation of the relationship between peripersonal space and supernumerary limb sensation in additive body augmentation.
Impact and Future Applications This research demonstrates that humans can genuinely experience artificial body parts as extensions of themselves through additive augmentation—not just replacement or substitution. These findings have significant implications for:
Assistive Technologies: Developing more intuitive prosthetics and robotic assistance systems
Cognitive Science: Advancing our understanding of human body schema plasticity
Industrial Applications: Designing augmentative systems for enhanced human capabilities
The work establishes cognitive transparency as a crucial design principle for supernumerary robotic systems and suggests new frameworks for understanding how the human brain adapts to incorporate additional body parts.
References
2022
Embodiment of Supernumerary Robotic Limbs in Virtual Reality
Ken Arai, Hiroto Saito, Masaaki Fukuoka, and 4 more authors
The supernumerary robotic limb system expands the motor function of human users by adding extra artificially designed limbs. It is important for us to embody the system as if it is a part of one’s own body and to maintain cognitive transparency in which the cognitive load is suppressed. Embodiment studies have been conducted with an expansion of bodily functions through a “substitution” and “extension”. However, there have been few studies on the “addition” of supernumerary body parts. In this study, we developed a supernumerary robotic limb system that operates in a virtual environment, and then evaluated whether the extra limb can be regarded as a part of one’s own body using a questionnaire and whether the perception of peripersonal space changes with a visuotactile crossmodal congruency task. We found that the participants can embody the extra-limbs after using the supernumerary robotic limb system. We also found a positive correlation between the perceptual change in the crossmodal congruency task and the subjective feeling that the number of one’s arms had increased (supernumerary limb sensation). These results suggest that the addition of an extra body part may cause the participants to feel that they had acquired a new body part that differs from their original body part through a functional expansion.
@article{araiEmbodimentSupernumeraryRobotic2022a,title={Embodiment of Supernumerary Robotic Limbs in Virtual Reality},author={Arai, Ken and Saito, Hiroto and Fukuoka, Masaaki and Ueda, Sachiyo and Sugimoto, Maki and Kitazaki, Michiteru and Inami, Masahiko},year={2022},month=jun,journal={Scientific Reports},volume={12},number={1},pages={9769},publisher={Nature Publishing Group},issn={2045-2322},doi={10.1038/s41598-022-13981-w},urldate={2025-05-30},copyright={2022 The Author(s)},langid={english},keywords={Computer science,Human behaviour,Perception},file={files/1030/Arai et al. - 2022 - Embodiment of supernumerary robotic limbs in virtu.pdf},category={peer-reviewed},}
People Come to Grips with Having an Extra Pair of Arms—in VR
@article{scientificamerican_vr_superlimbs,title={People Come to Grips with Having an Extra Pair of Arms—in VR},author={Warren, Sasha},year={2022},month=jul,journal={Scientific American},category={media}}
(Japanese article) Successful Embodiment of ’Third and Fourth Arms’ in VR Space: Could New Sensations Emerge in Metaverse Experiences Too?
@article{dglab_vrsl,title={(Japanese article) Successful Embodiment of 'Third and Fourth Arms' in VR Space: Could New Sensations Emerge in Metaverse Experiences Too?},author={Shoji, Kenichi},year={2022},month=sep,journal={DG Lab Haus},category={media}}
