Behavioral, physiological and subjective correlates of sleep onset
Date
1983
Authors
Perry, Thomas J. (Thomas John)
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The standard criterion used to judge a lapse of wakefulness is the disruption of electroencephalogram (EEG) alpha activity. Recent comparisons of alpha loss with functional abilities are found only in studies of sleep deprivation and vigilance detection. Earlier investigations of sleep onset in normal subjects were incompletely reported and left several questions unanswered about the general applicability of sleep onset criteria.
Twenty young adults, including seven females, were recruited from the university community to participate in two 2-hour polygraph sessions studying selected behavioral, physiological and subjective correlates of sleep onset. Experiment one compared passive closure of a telegraph key with changes in EEG alpha and theta activity, electrooculogram deflections, functions of thoracic and abdominal breathing components and subjective sleepiness ratings. Experiment two monitored the same physiological measures during a modified Wilkinson auditory vigilance test.
Subjects who produced abundant wakeful alpha activity had a mean latency of four sec from alpha loss to passive lapse (key closure) and a strong association of alpha level (present/absent) with key level (up/ closed). In these subjects alpha loss was also associated with significantly greater incidence of slow eye movements, reduced abdominal breathing, a larger ratio of thoracic to abdominal (TA) excursions and a longer expiratory time with respect to inspiratory amplitude. All subjects, regardless of either alpha abundance or sex, showed significant and similar associations of behavioral lapse with all of the above changes. Significant sex differences in breathing amplitudes, and overall results with respiratory variables, were discussed with reference to the history of experimental techniques and findings.
Results from use of the Stanford Sleepiness Scale (SSS) were inconclusive because of faulty data collection. A re¬plication attempt is indicated to confirm significantly sleepier mean ratings for both the key closed condition and the second half of the session, and an interaction in which SSS ratings were indistinguishably high during the second half.
In the second session the Wilkinson auditory vigilance test was administered at two levels of difficulty to different subjects. Misses were distinguished from correct detections (hits) by having a higher- numbered sleep stage during the four sec prior to tone delivery and both a lower abdominal amplitude and higher TA ratio in the preceding breath cycle. Only the subgroup that had the easy {400-500 msec) discrimination produced significantly more theta activity during the 1 sec prior to missed tones. Other variables failed to discriminate between hits and misses, and none of the variables distinguished hits from incorrect "detections" (false alarms), whether in component subgroups or for all subjects combined.
Analysis of differences in sensitivity, based on signal detection techniques and expressed as p(A), showed main effects for both task difficulty and sleep stage (W vs 1). An interaction also appeared in which the effect of stage upon sensitivity appeared only under the difficult discrimination (420-500 msec). The implications of this difference were discussed in terms of previous findings about rate of performance decrement across time as a function of signal in¬tensity. Also discussed were the role of threshold changes as a limiting factor on easy discriminations and a generally reduced discriminatory capacity with the progress of sleep onset.