Heart rate mechanisms in instrumental conditioning reinforced by petting in dogs.

The aim of this experiment was to determine heart rate (HR) responses during conditioned stimuli (CS) and the petting reward (US) delivered by the experimenter to the dogs after performance of the instrumental conditioned response (CR). It was found that in five dogs for which petting served as a positive reinforcement the delivery of petting was accompanied by cardiac deceleration followed by sudden acceleration at the moment of petting withdrawal. Presentation of CS evoked heart rate deceleration until performance of the first CR. At the start of performance of CRs, heart rate accelerated. It was suggested that heart-rate deceleration is an important component of cardiac response to petting reward and, that probably, it is associated with the hedonic aspect of the reinforcement.