"Feeling" the Stretch: Enhancing Embodiment in Virtual Arm Elongation Through Spatiotemporal Modulation of Visio-Haptic Feedback.

The perceived realism of virtual body illusions, such as arm elongation, is dependent on congruent sensory feedback. This paper explores the effects of visio-haptic stimulation on the sense of embodiment in Virtual Reality (VR). We conducted three experiments. The first identified the optimal parameters for vibrotactile feedback by varying stimulation location and motor activation duration (250, 500, 750 ms) during a fixed visual task of 40% arm elongation over 18 seconds. We found that sequential stimulations along the entire arm with a 500ms duration per motor were the most effective. From this, we derived a formula to generalize the optimal haptic timing based on elongation velocity. The formula was then validated in two follow-up experiments: one varying the elongation percentage (26% to 80%) and another varying the elongation duration (9s to 27s). Our findings offer validated guidelines for designing more immersive haptic experiences for virtual body deformations.