The cardiac orienting response and its relationship to the cardiac conditional response in dogs

Orienting tones of two durations (11 seconds and 42 seconds) were presented to two groups of dogs, and the heart rate-orienting responses (HR-OR) were measured. With the brief tone (11 seconds) the initial HR-OR was usually a bradycardia. With the longer tone (42 seconds) the HR-OR was a biphasic response, an initial bradycardia followed by a tachycardia. The bradycardia component extinguished more rapidly than the tachycardia component of this response. The bradycardia also extinguished more rapidly to the long tone than to the brief tone. With the brief tone the degree of HR-OR was not highly correlated with the degree of HR conditional response given by the same dog after the tone had been reinforced by shock.