AbstractSocial touch refers to the sensory processes related to the observation of physical interactions between individuals or between individuals and the environment. Indeed, observing a hand touched by an object or another hand led to increased somatosensory activation compared to observing contactless interactions (Schaefer et al., 2009; Pisoni et al., 2018). However, it is unclear whether the kinematics of the observed interaction modulates such somatosensory activation and whether such modulation is dependent on the moving and contact receiving object. In three experiments, participants observed either a slow- or fast- moving hand or ball at the top of the screen, contact either a hand or leaf at the bottom of the screen. To infer somatosensory activation, participants reacted to an auditory beep at the moment of observed contact. If observed contact led to increased somatosensory activation, response times (RTs) would decrease due to intersensory facilitation (Forster et al., 2002). In Experiment 1, RTs were lower when observing fast compared to slow hand movements, regardless of the target (i.e., hand or leaf). In Experiment 2, RTs were lower when observing fast compared to slow ball movements, but the size of effect was larger when a hand was the target compared to a leaf. In Experiment 3, RTs were lower when observing fast compared to slow movements toward a leaf, regardless of the moving object (i.e., hand or ball). Overall, this study provides evidence that observed movement speed influences somatosensory activation and its influence is dependent on the moving and contact receiving object.
Acknowledgments: University of Toronto, Ontario Research Fund, Canadian Foundation for Innovation, National Sciences and Engineering Research Council