The kinaesthetic mirror illusion: How much does the mirror matter?
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The reflection of a moving hand in a mirror positioned in the sagittal plane can create an illusion of symmetrical, bimanual movement. This illusion is implicitly presumed to be of visual origin. However, muscle proprioceptive afferents of the arm reflected in the mirror might also affect the perceived position and movement of the other arm. We characterized the relative contributions of visual and proprioceptive cues by performing two experiments. In Experiment 1, we sought to establish whether kinaesthetic illusions induced using the mirror paradigm would survive marked visual impoverishment (obtained by covering between 0 and 100 % of the mirror in 16 % steps). We found that the mirror illusion was only significantly influenced when the visual degradation was 84 % or more. In Experiment 2, we masked the muscle proprioceptive afferents of the arm reflected in the mirror by co-vibrating antagonistic muscles. We found that masking the proprioceptive afferents reduced the velocity of the illusory displacement of the other arm. These results confirm that the mirror illusion is not a purely visual illusion but emerges from a combination of congruent signals from the two arms, i.e. visual afferents from the virtually moving arm and proprioceptive afferents from the contralateral, moving arm.
KeywordsKinaesthesia Mirror illusion Muscle proprioception Visual impoverishment
We thank Dr. David Fraser (Biotech Communication, Damery, France) for improving the manuscript’s English and Dr. Jean-Luc Roulin for his help in setting-up Experiment 1.
The work was funded by the University Savoie Mont Blanc (Chambéry, France).
Compliance with ethical standards
Conflict of interest
None of the authors have any conflicts of interests.
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