Tone Intensity and Rise‐Decay Time Effects on Cardiac Responses During Sleep

If the prolonged orienting response, reflected in monophasic cardiac deceleration, indicates attention to stimulus inputs, it should not be easy to evoke the response during sleep. Two experiments confirmed and extended previous work showing that the heart rate response in sleep is primarily accelerative. Acceleration occurred with low intensity. 1000 Hz tones of gradual onset and even to tone offsets when either tone onsets or offsets also elicited a K‐Complex. In the absense of a K‐complex, there were no significant or consistent changes. Since the accelerative component was present on the first trial, habituation could not account for its appearance. It was concluded that the sleep response probably does not reflect an orienting response.