Squeeze me, but don't tease me: human and mechanical touch enhance visual attention and emotion discrimination.

Being touched by another person influences our readiness to empathize with and support that person. We asked whether this influence arises from somatosensory experience, the proximity to the person and/or an attribution of the somatosensory experience to the person. Moreover, we were interested in whether and how touch affects the processing of ensuing events. To this end, we presented neutral and negative pictures with or without gentle pressure to the participants' forearm. In Experiment 1, pressure was applied by a friend, applied by a tactile device and attributed to the friend, or applied by a tactile device and attributed to a computer. Across these conditions, touch enhanced event-related potential (ERP) correlates of picture processing. Pictures elicited a larger posterior N100 and a late positivity discriminated more strongly between pictures of neutral and negative content when participants were touched. Experiment 2 replicated these findings while controlling for the predictive quality of touch. Experiment 3 replaced tactile contact with a tone, which failed to enhance N100 amplitude and emotion discrimination reflected by the late positivity. This indicates that touch sensitizes ongoing cognitive and emotional processes and that this sensitization is mediated by bottom-up somatosensory processing. Moreover, touch seems to be a special sensory signal that influences recipients in the absence of conscious reflection and that promotes prosocial behavior.