Is This My Hand? : Exploring the Influence of Hand Model Realism on the Virtual Hand Illusion

Since the introduction of virtual reality (VR), the perceptual rules to invoke Body Ownership Illusion (BOI), which is the feeling that a fake body part is your own, have been challenged. This study investigated how humanoid plausibility affects BOI by comparing realistic and non-realistic hands in a Virtual Visuo-Motor Hand Illusion (VMHI) experiment. BOI scores of the non-realistic hand were compared with immersive tendencies scores, as it was hypothesised to correlate with higher BOI scores for the non-realistic hand. Seventeen participants were assigned to either a realistic or non-realistic hand condition in a 2x2 mixed design. Each experienced both static and synchronous visuomotor stimulation. BOI, agency and immersive tendencies were measured. Results showed significantly higher BOI and agency scores in the synchronous condition, reinforcing the critical role of temporal synchrony. Unexpectedly, the non-realistic hand produced higher, though non-significant, BOI scores than the realistic hand, potentially due to technical issues and an uncanny valley effect evoked by the realistic hand model. No significant correlation was found between immersive tendencies and BOI for the non-realistic hand. Agency was not influenced by hand realism, supporting the idea that motor control, rather than appearance, holds more importance for agency. These findings suggest that humanoid plausibility may not always enhance BOI in VR and that immersive tendencies cannot override it. Through the various limitations, the study highlights the importance of predictive coding, the uncanny valley effect, and methodological precautions for future VHMI research.