Abstract: | Human subjects were conditioned to a tone-shock sequence during heat or cold exposure and then given 10 trials of experimental extinction in the heat. In the heat, while exhibiting a general peripheral as well as a digital vasodilatation, vasoconstriction developed as a conditioned response; the response did not extinguish. In the cold, with general peripheral and digital vasoconstriction, vasodilatation developed as the conditioned response. Since the cold-conditioned Ss did not recover completely from their cold exposure during the following heat equilibritun period, the extinction data of this group could not be accepted. A comparison was also made of the differences in thermoregulation and in conditioned responses of preselected Ss varying in latency of cold-induced digital vasodilatation. Although these Ss did differ in their thermophysiological reactions, they did not differ in regard to the nature of the conditioned response developed. |