Examining constraints on embodiment using the Anne Boleyn illusion

Area of Science:

• Neuroscience
• Cognitive Psychology
• Body Perception

Background:

• Illusory embodiment, or the sense of owning a non-existent body part, is a key phenomenon in understanding body representation.
• The Anne Boleyn illusion, involving a perceived sixth finger, offers a unique paradigm to investigate the limits of this embodiment.

Purpose of the Study:

• To explore the anatomical and postural constraints on illusory embodiment using the Anne Boleyn illusion.
• To determine the factors that support or diminish the sense of owning an illusory sixth finger.

Main Methods:

• Experiment 1: Manipulated anatomical features (finger shape) and postural congruence between the real and mirrored hand.
• Experiment 2: Varied the orientation, shape, and length of the illusory sixth finger to test extreme conditions.
• Utilized concurrent visuotactile stimulation (stroking) to induce and maintain the illusion.

Main Results:

• The Anne Boleyn illusion proved surprisingly robust, persisting even with anatomically unusual or mismatched hand postures.
• Significant diminishment of the illusion occurred only when the illusory finger was spatially distant or in highly implausible orientations.
• Visuotactile input and the 'blank canvas' of empty space appear crucial for this robust embodiment.

Conclusions:

• Human body representations are exceptionally flexible, accommodating embodiment of empty space under various conditions.
• Concurrent visuotactile stimulation plays a critical role in overriding anatomical and postural expectations for body ownership.
• The findings challenge existing models of body illusions, highlighting the adaptability of the brain's self-representation.