Monotonous stimulation, sleep onset and habituation of the orienting reaction

Abstract

The aim of the study was to assess the effects of monotonous stimulation on arousal and sleep onset. Thirty subjects were examined in a condition of repetitive auditory stimulation, and a control condition of no such stimulation. Recordings were taken of EEG and skin conductance. EEG measures showed that sleep onset was faster, that more sleep occurred, and that it developed more rapidly during the experimental than during the control condition. The skin conductance data, i.e., conductance level and frequency of spontaneous responses, were in accordance with the EEG results. Theoretically, the results were related to formulations about the habituation of the orienting reaction (OR), according to which common mechanisms are responsible for OR habituation and sleep onset. Some support for the adequacy of this theoretical framework was obtained from the correlation coefficient between time to sleep onset and time to habituation of skin conductance responses to tones, which was found to be significant. A second experiment was designed to test the notion of interdependence between OR habituation and sleep onset. It was hypothesized that, by manipulating the time to habituation, time to sleep onset would be similarly varied. To produce variations in habituation time, three different groups of twelve subjects each were given three different frequencies of stimulation. A control group, not receiving the auditory stimulus was also run. The results verified the hypothesis of parallel effects of frequency of stimulation on OR habituation and sleep onset, i.e., both were faster with more frequent stimulation. In addition, the findings from the first experiment regarding time to sleep onset during stimulation, as compared to no stimulation, was confirmed.