Abstract
In this study, we use the paradigm of the Rubber Hand Illusion (RHI) to investigate the representation of size in the body-schema. In RHI manipulations, a visually presented rubber hand is stroked in synchrony with the hidden hand of the participant to create a visuo-tactile ‘conflict’ that results, through the dominance of vision, in the illusion that the tactile sensations stem from the visually specified but inanimate rubber hand. In this experiment, we varied the size of the rubber hands in this procedure, employing a large or a small hand, according to the condition. After three minutes of synchronous or (control) asynchronous stroking to the real and rubber hands, we had participants estimate real hand size using a template-matching task or we had them make a reach-and-pincer movement to a pair of dots. From data due to 20 consecutively recruited healthy volunteers who each sat all conditions, we found that synchronous stimulation to both the small and large hands resulted in significantly different hand-size estimation to that after asynchronous stimulation: in the big-hand condition participants overestimated hand-size and in the small-hand condition participants underestimated hand-size. We found just in the big-hand condition that participants' pincering behaviour was modified: participants who had viewed a big hand being synchronously stimulated made significantly smaller pincer-movements than those in the equivalent control condition. We discuss the implications of these results for the representation of body-size and its relationship to the representation of peripersonal space.