Watching touch increases people’s alertness to tactile stimuli presented on the body surface

Several studies have shown that watching one’s own body part improves tactile acuity and discrimination abilities for stimuli presented on that location. In a series of experiments we asked the participants to localize tactile stimuli presented on the left or right arm. In Experiment 1 the participants were not allowed to watch their body, but they could see another person’s left arm via a LCD display. This arm could be touched or not during the presentation of the stimuli. We found that when the participants saw the arm on the screen being touched, their responses to the tactile stimuli presented on the left and on the right arm were faster and more accurate than when the arm on the screen was approached but not touched. Critically, we did not find any illusion of ownership related to the hand seen on the screen. In Experiments 2 and 3 we varied the position of the screen with respect to the participant’s body midline and the image displayed on it (an arm or an object of equal size). The participants gave faster responses when an object rather than a hand was displayed on the screen. Moreover, the responses were slower when the hand on the screen was placed in front of the participants, as compared to any other position. Taken together the results of our experiments would seem to suggest that watching touch activates multisensory mechanisms responsible for alerting people regarding the possible presence of tactile stimuli on the body surface.