Touching my face with my supernumerary hand: a cheeky illusion

A self-touch paradigm elicits a surprising illusion. With the participant's eyes closed, the examiner guides the participant's right index finger to administer strokes and taps to the right side of the participant's face. At the same time, the examiner strokes and taps the corresponding location on the left side of the participant's face. Although the participant administered touch to only the right side of the face, this paradigm elicited the illusion of self-touch to both sides of the face, and the illusion often implicated a third, disconnected or disembodied, hand. We propose an explanation, and draw parallels with the phenomenon of supernumerary phantom limb.