Abstract
In neuropsychological literature, numerous case studies suggest two separate body representations in the brain; one for perception, called the body image, and one for action, called the body schema. Rubber hand illusion and tool-use paradigms have been used frequently in the last twenty-five years to investigate these body representations, respectively, with minimal overlap between the fields. However, interactions between these paradigms are probable, considering the common sensory modalities targeted by the techniques used for measuring their effects. Here, we combined rubber hand illusion and tool-use paradigms in a novel behavioral experimental setup (N=72) and comparatively examined the resulting changes in body representations through measures of forearm bisection (for body schema), proprioceptive drift, and subjective experience questionnaire (for body image). Specifically, after a tool-use task where subjects actively used a grabber tool with their right hand to move cubes close to or away from their body, we observed a change in the metric representation of the right forearm length depending on the length of the tool used (using the long tool resulted in an increase in perceived forearm length). Subsequent to the tool-use task, the “tool-holding” rubber hand illusion, where the experimenter stroked the tip of the tool held by the rubber hand either synchronously or asynchronously to that of the tool held by the subjects, also resulted in perceived forearm elongation if the subject observed a longer tool held by the rubber hand. Follow-up experiments showed that the forearm elongation effect that occurred during rubber hand illusion depended on prior active use of the tool, embodiment of the observed hand and tool, and a length disparity between the held and observed tools, which together revealed that the representation of forearm length, a component of body schema, can be modified through changes in body image.