The rubber hand illusion and the tactile Simon effect

Abstract

We examined the effects of the rubber hand illusion on representing tactile stimuli using the Simon effect. In a tactile Simon effect task, participants are instructed to make intensity judgments (using foot pedal responses) to tactile stimuli presented to the hands. Participants are faster when the tactile stimulus and response foot are on the same versus opposite side of the body, regardless of whether the limbs are crossed or uncrossed. Furthermore, participants are faster overall when the hands are crossed versus uncrossed. In this study, participants engaged in a tactile Simon effect experiment with rubber hands positioned directly above the participants’ hidden hands, and with real and rubber hands stroked before each experimental block. Each participant was tested in four blocks, manipulating real and rubber hand position (crossed or uncrossed). First, we found that participants responded faster with real or rubber hands crossed, demonstrating that crossing the hands (real or rubber) can hasten tactile intensity judgments. Furthermore, on trials when the rubber hands were crossed, high ownership ratings for the rubber hand were significantly correlated with faster reaction times. Finally, we found a significantly more robust Simon effect when the rubber hands (but not real hands) were crossed. We discuss these findings with reference to how integration of rubber hands into the body schema influences how we represent the location of tactile stimuli.