Thermal stimulus thresholds: sources of variability.

Thresholds to warming and cooling by a small Peltier stimulator were measured and remeasured in 24 adults and children aged 7-9. The median thresholds to warming and cooling of the forearm were +1.04 and -.15 degrees C. respectively, and neither age nor sex mattered significantly. The test-retest correlation was significant, suggesting intra-subject reliability, despite a large range of thresholds across subjects-about an order of magnitude. Measurements of skin temperature revealed that the same stimulus can cause a greater degree of warming or cooling in one subject than another. These differences proved reliable on retesting. Surprisingly, however, there was no correlation between this physical variation among people and the size of their psychophysical thresholds. Some compensatory mechanism is suggested by these data; the implication is that people who are less responsive physically may be more sensitive neurally and vice versa.