Following stroke, a patient may fail to report touch administered by another person but claim that s/he feels touch when it is self-administered. In Part One, the self-touch rubber hand paradigm was used to investigate different explanations for this phenomenon, termed self-touch enhancement. The most important finding was that patients reported touch based on feeling rather than by using proprioceptive information. Some patients have residual sensation that could be targeted in sensory rehabilitation. Part Two is a systematic investigation of the illusion of self-touch conducted with neurologically healthy participants. Participants used the right hand to administer touch to a prosthetic hand while the left (receptive) hand, positioned 15 cm from the prosthetic hand, received Examiner-administered touch. Proprioceptively perceived position of the administering and receptive hand was measured. Most participants experienced the single event of self-touch at the location of the receptive hand. Previous investigations have relied on measurement of only one hand and have concluded that participants experience self-touch at the location of the prosthetic hand. Our findings have implications for the role of ownership in this illusion. There is also a series of experiments in Part Two which test four potential constraints on the illusion of self-touch – violated expectations about the object that is administering touch, increased distance between the hands, alignment mismatch, and anatomical implausibility. For example, one study uses a novel paradigm to demonstrate that, although the subjective intensity of the illusion of self-touch is diminished by anatomical implausibility, most participants report the impossible experience of touching their left elbow with their own left index finger. Taken together, these experiments highlight the malleability of body representation, and provide a comprehensive framework for understanding the illusion of self-touch.
