This paper describes a new psychophysical technique for the measurement of experimentally induced pain. Signal detection theory provides two indices of the subject's performance. The physiological parameter, d′, provides the measure of sensory sensitivity, on discriminability. Thus any maneuver, for example, the administration of a local analgesic, which reduces neural transmission, would be expected to decrease d′. This effect was found following a partial block of the median nerve by dilute Carbocaine HC1. The psychological parameter, Lx, locates the subject's report criterion, that is, his willingness or reluctance to report the presence of pain. For example, the placebo-induced suggestion that the subject would be able to endure more pain raised the criterion, Lx, (fewer pain reports). In the present study, acupuncture raised the pain report criterion, Lx; however, it failed to alter d′. These results suggest that decreases in pain report following electro-acupuncture may be caused by suggestion, not by analgesia.
