Influencing non-verbal expressions of pain: Signal detection analyses

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Abstract
Non-verbal expressive behavior may provide important information about pain not available through verbal report. It has received little attention in pain research. Changes in expressive behavior resulting from electric shock were related to shock intensity, self-report of discomfort, observers'' judgments of subjects'' distress and social modeling influences. Subjects were videotaped while they rated low-, medium- and high-intensity shocks. Simultaneously, they were exposed to a tolerant social model or an inactive companion. Observers then viewed videotapes of subjects and judged the level of shock being delivered on the basis of non-verbal behavior. Observers'' judgments were analyzed by signal detection methods to quantify expressive behavior. Change in expressive reactions to the shocks was directly related to stimulus intensity, self-report of pain and observers'' judgments of subjects'' distress. Expressive behavior resulting from high shocks was diminished by exposure to a tolerant model. These findings that expressive behavior provides a sensitive and valid index of pain, and indicate that tolerant modeling reduces evidence of pain across multiple measures.