Demand characteristics underlying differential ratings of sensory versus affective components of pain.

In several investigations, differential ratings of sensory and affective components of pain can be explained by the expectations conveyed to subjects to provide different ratings for each pain component under conditions where they could readily recall their ratings. In Experiment I, such demand characteristics were controlled in one group by having subjects rate each pain component in a separate session 1 week apart, so as to minimize recall. This group failed to differentiate between sensory and affective pain; however, another group with demand characteristics left uncontrolled, provided disparate and parallel functions for the two pain components. These results imply that recall during concurrent ratings of the two pain components contributes to a spurious separation of ratings for each component. In the second study, with demand characteristics controlled, a medication placebo led to ratings of affective pain that were significantly lower than those for sensory pain, and a divergence between the functions for each component. This offers an approach to the veridical separation of sensory and affective components of pain.