Modulating observer's pain by manipulating the diagnosticity of face stimuli for the recognition of the expression of pain

Abstract

Recent findings suggest that the emotional valence of visual stimuli can modulate pain perception (Rhudy et al. 2005); unpleasant images increase pain reports, while pleasant images has the opposite effect. Here, we modulated the observer's perception of acute shock-pain by varying the information provided to recognize the pain facial expression (unpleasant stimuli). Last year at VSS, Roy et al. (Abstract 710) described the visual information subtending the recognition of the facial expression of pain. Based on these results, we created two masks: one revealing the more useful (top 5 %) information for the identification of pain expression (optimal mask) and one revealing the less useful information (bottom 5%—neutral mask). Twenty stimuli were created by applying these masks to ten different static facial expression of pain. A pilot study ensured that the optimally-masked stimuli led to the perception of negative emotions while the neutrally-masked stimuli led to the perception of positive emotions. Twenty-four normal volunteers received transcutaneous electrical stimulation of the sural nerve (30 ms) at the offset of each visual stimulus (1 s), and were asked to rate the intensity and the unpleasantness of shock-pain on visual analog scales. Preliminary results show that pain intensity and unpleasantness are judged less intense when the shock is given after the neutrally-masked stimuli than after the optimally-masked stimuli. These results are consistent with an effect of emotional valence on pain perception and may explain the hyperalgesic effects induced by the perception of pain in others reported in studies on pain empathy.