DISCRIMINABILITY OF ELECTROCUTANEOUS STIMULI AFTER TOPICAL ANESTHESIA- DETECTION-THEORY MEASUREMENT OF SENSITIVITY TO PAINFUL STIMULI

In three experiments on the psychophysical measurement of pain, electr ocutaneous currents were applied to the volar surface of the forearm. In the first experiment, a conventional category scaling method was co mpared with the rating method of signal detection. The results of both methods were analyzed in detection-theory terms to derive receiver op erating characteric curves and measures of the discriminability of adj acent currents. The rating method yielded larger discriminability valu es than the category scale did, and that method was therefore used in the subsequent experiments to examine the effect of a topical anesthet ic on discriminability. When the stimuli were applied through surface electrodes, no effect of the topical anesthetic on discriminability wa s found, but when the stimuli were applied to a more localized area by intradermal needle electrodes, a dose-dependent effect of the anesthe tic on discriminability occurred. For this experiment, the slope of th e cumulative sensitivity function increased with increasing elapsed ti me since the removal of the anesthetic. This result is congruent with the theory that discriminability can serve as a measure of sensitivity to painful stimuli.