Abstract
Considering that humans recognize mirror images as copies of the real world despite misinterpreting optical reflections, spatial disagreement may be accepted in rubber hand illusion (RHI) settings when a mirror is used to show a fake hand. The present study performed two experiments to reveal how self-body recognition of a fake hand via a mirror affects RHI. First, we tested whether illusory ownership of a fake hand seen in a mirror could be induced in our experimental environment (screening experiment). Subjective evaluations using an RHI questionnaire demonstrated that embodiment of the rubber hand was evoked in the presence or absence of a mirror. We then examined whether using a mirror image for RHI allows disagreement in orientation (45 ∘ ) between the rubber and actual hands (main experiment). The participants experienced RHI even when the actual and rubber hands were incongruent in terms of orientation. These findings suggest that using a mirror masks subtle spatial incongruency or degrades the contribution of visual cues for spatial recognition and facilitates multisensory integration for bodily illusions.
Highlights
The rubber hand illusion (RHI) is a phenomenon in which body ownership of a fake hand is illusorily experienced when a visible fake hand and occluded veridical hand are exposed to spatially and temporarily congruent visuotactile stimuli
This study investigated the role of gazing at a fake hand in a mirror under RHI conditions with the hypothesis that the mirror image moderates the requirements of spatial congruency
The illusory experiences of body ownership and agency were evoked in our experimental environment when the spatially congruent fake hand in a mirror was gazed at, which agrees with earlier studies
Summary
The rubber hand illusion (RHI) is a phenomenon in which body ownership of a fake hand is illusorily experienced when a visible fake hand and occluded veridical hand are exposed to spatially and temporarily congruent visuotactile stimuli. Since Botvinick and Cohen [1] first reported this phenomenon, the RHI paradigm has been used in studies on multisensory integration and body ownership. In this paradigm, congruency among multiple sensory cues is important [2,3]. According to Constantini and Haggard, a hand angle mismatch of 20o between the veridical and fake hands distracts from the body ownership illusion [6]. This angle value varies among studies [9,12]
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