Areal and temporal summation in the thermal reaction time.

It has previously been shown that the reaction time (RT) to radiant heat measures spatial summation of warmth, because the RT decreases with increases in both the areal extent and the intensity (flux density) of the heat. The previous studies of RT let the response terminate the stimulus exposure and thus introduced a confounding between stimulus duration and intensity, since the weaker the stimulus is, the longer it is presented. The present study shows the RT reflects spatial summation even with a fixed, brief stimulus duration. The precise rules for trading area and intensity that are obtained with fixed-duration pulses differ from those obtained with response-terminated ones, but both sets of functions are consistent with each other and with the results of magnitude estimation if it is assumed that the sensory effect of the heat sums over the stimulus duration, that is, that the RT reflects temporal as well as spatial summation. Two further experiments provide direct evidence for temporal summation.