Virtual Hand Illusion: The Alien Finger Motion Experiment

Abstract

In Virtual Reality, the need to understand how subjects perceive their representation is gaining attention and importance. We present a contribution to a better understanding of the sense of embodiment by assessing two of its main components, body ownership and agency, through an experiment involving alien motion. The key aspect of the experimental protocol is to integrate a condition with some personalized alien finger movement while the subject is asked to remain still. Body ownership appears to be significantly reduced, but not agency. We also propose a metric to assess quantitatively that the view of the alien movement induces more finger posture variation compared to the reference context in the still condition.

The Induced Finger Movements Effect

“…16 volunteers took part to the experiment, 14m and 2f, age µ =28.8, σ =7.0. Following the method presented by [Soccini et al 2019], we defined an experiment in two phases. In Phase1 we asked users to look at their right palm while opening and closing their hand at their favorite pace.…”

“…We quantified the SoE using the questionnaire proposed by [Soccini et al 2019]. While in Phase1, the real time visualization provided a significant SoE (p<0.01) despite the alien motion, while in Phase2, the presence of a delay canceled the SoE (p=0.58).…”

“…For each phase, we quantified the movements of the users during the 18 periods of alien motion, and distinguished the natural movements from those induced by the presence of alien motion in the setup, using the quantifier D proposed by [Soccini et al 2019]. In Phase1, we assessed the existence of some movements that were likely to be induced by the visualization of the alien motion, as they differed from the data collected as a baseline.…”

“…Regarding alien motion, [Shibuya et al 2018] introduced the concept of 'motor back projection' as the transfer of the movement of an illusory embodied body part to the sensorimotor system of the observer. In VR, an analogous phenomenon was spotted and quantified by [Soccini et al 2019], while [Gonzalez Franco et al 2020] presented a review on the so-called self-avatar follower effect. Following the work of [Soccini et al 2019], that presented the induced movements effect in case of embodiment, we show that the effect disappears in case of disembodiment, i.e.…”

“…In VR, an analogous phenomenon was spotted and quantified by [Soccini et al 2019], while [Gonzalez Franco et al 2020] presented a review on the so-called self-avatar follower effect. Following the work of [Soccini et al 2019], that presented the induced movements effect in case of embodiment, we show that the effect disappears in case of disembodiment, i.e. in case of a delayed visualization of the movements of the avatar.…”