Referred sensations induced by a mirror box in healthy subjects

Twenty-one healthy subjects were instructed to observe the mirror image of the tactile stimulation of their own hand (control condition) or an assistant's hand (experimental condition) while being queried about the referred sensation (RS) in their own masked hand behind the mirror. The rated intensity of the RS under the experimental condition was significantly stronger than that under the control condition. In a second experiment, the experimental condition was replaced with the tactile stimulation of a prosthetic (rubber) hand, and was compared with the tactile stimulation of the subject's own hand (control condition). In both of the experiments, the rated intensity of RS was significantly stronger under the experimental condition than under the control condition. The qualitative characteristics of the induced RS on the mirror image hand--including the location, sense of ownership, and various subjective feelings--were also found to vary among subjects. In conclusion, an RS could be induced in healthy subjects on the mirror image of the hand by tactile stimulations, although this effect differed substantially among individuals.