Comparing bodily illusions: the rubber hand illusion and the mirror illusion
Summary
Different mental representations of the body have been proposed by different researchers. A common distinction between body representations is between the body image (perceptual responses) and the body schema (motor responses). In this study the difference between these two representations is investigated by using two bodily illusions, the rubber hand illusion and the mirror illusion. In the rubber hand illusion subjects view stimulation of a rubber hand while feeling synchronous stimulation on their own hand, which may lead to the feeling that the rubber hand is part of their own body. In the mirror illusion subjects view stimulation of the reflection of their own hand while feeling synchronously stimulation of their occluded other hand. Subjects may feel that the reflection of the seen hand is their occluded hand. Because previous studies yield different results (the mirror illusion does seem to have influence on reaching responses, and the rubber hand illusion does not), in this study both illusions are compared. After stimulation (synchronously or asynchronously inducing or not inducing the illusion, respectively) in one of both illusions subjects performed perceptual and motor responses, which are argued to be based on the body image and the body schema, respectively. Results showed that inducing the illusion influences the perceptual response (perceived location) of the stimulated hand significantly more than not inducing the illusion. The rubber hand illusion and the mirror illusion differ significantly in the perceptual response, with the mirror illusion having a stronger effect. Inducing the illusion does not influence the reaching movement with the right stimulated hand towards the left hand, and the type of illusion does not have an effect on the reaching response. Both illusions seem to influence the body image, and not the body schema in this particular set-up.