Temporal summation of pain from radiant stimulation

Latency thresholds of pricking pain, using radiant thermal stimulation, were obtained. Ten Ss were tested for 10 sessions, and, in each session, single latency determinations were made at each of 10 stimulus intensities. Each intensity was administered to a different spot along the volar surface of S’s nonpreferred forearm. Thus, 10 latency thresholds were obtained from each S at. each intensity and each spot. Initial skin temperature was controlled so that a threshold determination was made when skin temperature measured 33.5° ± 0.5° C. Analysis of variance of the log₁₀ t (seconds) values revealed a highly significant linearity of regression of log t on log intensity, thus confirming the hypothesized inverse and exponential relationship between latency and intensity. The parameters (slope and x-intercept) of the curve were discussed. The x-intercept may be interpreted as an index of an aversive threshold and could be used as a possible measure of the physiological component of pain.