The heart rate component of the social reflex in dogs: The conditional effects of petting and person

Five dogs were given a 480-cps tone followed by shock for more than 200 trials. A 200-cps tone was then introduced followed by a person petting the dog at the end of the conditional signal (CS) for 50 trials. Finally, the 480-cps tone-shock (T-S) sequence was reintroduced for five trials, after which the person entered the experimental room and stood beside the dog during one additional T-S sequence. It was observed that both the heart rate (HR) increase to shock, and the HR decrease to petting could be conditioned rapidly (1–5 trials). These findings are discussed in terms of the theory of stimulus substitution in classical HR conditioning. After the person had been made part of a CS for petting, and the T-S sequence reintroduced, the HR increase during the CS was reduced. The HR response to the shock, however, was greater than the response to this US when the dog was alone. A control group, given the same T-S sequence with a person present who had not been a CS for petting, did not show any significant HR changes from the usual response given to the T-S sequence. It is emphasized that these findings, in conjunction with earlier reports, indicate that the cardiovascular system may be a valuable index in studying the psychophysiology of socialization processes.