Motivation and expectancy factors in symptom perception: a laboratory study of the placebo effect.

Placebos are widely recognized as having a potentially powerful effect on health and health behavior, yet our understanding of the placebo phenomenon is limited. Many factors are considered to be associated with placebo responding. This study was designed to examine, in a laboratory context, the effects of two of these factors, motivation and expectation, on one kind of placebo response, that which involves the perception of symptoms. The results point to the importance of motivation in influencing the perception of symptom change, and provide limited support for the importance of expectation. The findings underscore the necessity for examining placebo effects from a multicomponent perspective, and appear to mandate the inclusion of both expectancy and motivation factors in future process and outcome studies.