Dissociating spontaneous and deliberate expressions of pain: signal detection analyses

Neuro-anatomical and behavioral findings suggest that spontaneous and deliberate facial expressions are regulated by separate systems. The present study examined whether spontaneous and deliberate expressions of pain could be distinguished and, if so, the dimensions on which they differ. Forty subjects were exposed to electric shocks that varied from painless to strong pain. They also simulated facial reactions to the same levels. Observers rated the apparent pain in subjects' expressions and whether they were feigned or genuine. Signal detection analyses indicated that the intensity of deliberate expressions was greater than spontaneous expressions at levels below strong pain. Observers were able to distinguish between deliberate and spontaneous expressions to a modest degree. The intensity of deliberate expressions was related to role-playing ability. The results suggest that deliberate and spontaneous expressions of pain probably differ in intensity, topography and temporal features. They suggest that facial expressions of pain have different determinants than other forms of pain behavior.