How fast should the night shift rotate?

Claims are frequently made that changing from morning to afternoon to night shift at about two- to three-day intervals (rapid rotation) is the best way of organizing 24h staffing. A critical analysis is made of the grounds for these assertion, followed by a review of evidence bearing upon the issue of whether longer periods of rotation are to be preferred. The conclusion is that permanent (zero rotation), fixed-night systems are superior on most counts, and should be implemented for night work, leaving the option of rapid rotation to cover the two (morning and afternoon) day shifts. This said, the multiplicity of shift systems and settings means that this will not always be the method of choice. Furthermore the recommendation should be regarded as provisional pending a search for more data directly comparing the two systems.

Response-stimulus interval in choice serial reaction time: interaction with sleep deprivation, choice, and practice.

In choice serial reaction time (RT), Response-to-next-Stimulus Interval (RSI) was varied from 0 to 600 msec in 40-msec steps. In three experiments, RT fell and errors rose as RSI was increased to 480 msec; they remained unchanged thereafter. The effect of RSI on RT was not linear, was reduced by 6- as compared with 4- or 3-choice responding, and was unaffected by sleep deprivation, despite loss of sleep reducing RT overall. The effect of penultimate RSI on RT was similar to that current RSI, but smaller. Two explanations of RSI--response-generated kinaesthetic feedback blocking a "central processor" and a preparatory interval as in warned simple RT--are rejected. Instead, the idea of "relative refractory state" is revived but now, because of the RSI/error finding, biased more towards responding than stimulus reception and encoding. In all three experiments the influence of RSI on RT was reduced with practice. If practice encourages automatic rather than controlled processing (Shiffrin & Schneider, 1977), the prediction is that the former will show less refractoriness.

The detection of sleep onset: behavioral, physiological, and subjective convergence.

In this report, a sleep deprivation/multiple arousal paradigm was used in which response time (RT) and respiratory and electroencephalographic (EEG) measures were combined with a continuous behavioral index of arousal (a deadman switch) and frequently repeated Stanford Sleepiness Scale ratings to examine the process of falling asleep. Sleep was defined behaviorally as failure to respond to the faint auditory RT cue. Although response rates decreased significantly as EEG stages passed from W through 1 to 2, responding continued in both light "sleep" stages. Respiratory, subjective, and DM changes were more pronounced between Stages W and 1 than between Stages 1 and 2. If the criterion for wakefulness is cognitive response to external stimulation, accurate distinctions between sleep and wakefulness can only be made in EEG Stages 3, 4, and rapid eye movement sleep. If EEG is the criterion, then the data suggest that cognitive response is possible during Stages 1 and 2 "sleep". The concept of a Sleep Onset Period, characterized by lengthening response times and intermittent response failure (thereby reflecting neither true sleep nor wakefulness), may provide a useful resolution to this definitional dilemma.

Age and simple reaction time: decade differences for 5,325 subjects.

In a booth at a public exhibition entitled "Medicines for Man," 5,325 men, women, and children carried out a 1-minute test of simple reaction time (RT) with 1 to 10 second randomized variable preparatory interval (PI). They recorded their ages by decade. Average RT over the last eight (of ten) trials increased progressively from the 20s up to age 60 and over, and downward to the teens and under 10s. The single fastest RT in each test varied much less with age, only the 20s being clearly faster than the rest, with the under 10s slower. Within-subject variability of RT was increased only in the under 10s and over 60s. Ability to sustain attention during the longer PIs may underlie the gross average RT differences with age, and possibly some more basic neural property the superiority of the 20s in fastest RT.

Behavioral versus EEG-based monitoring of all-night sleep/wake patterns.

Faint tones were presented at intervals (average 16 s) throughout a night's sleep; whenever they heard them, subjects pressed a palm-mounted button to switch them off. At the same time, electroencephalogram (EEG) was recorded. Button-press responses occurred in all EEG stages of sleep except Stage 4, although there was only one behavioral response (BR) in Stage 3 and one in REM. The mean probability of response (PR)/Stage was Stage 1 = 0.235, Stage 2 = 0.016, Stage 3 = 0.001, Stage 4 = 0.000, Stage REM = 0.0004. Also, responses sometimes failed to occur in EEG Stage wake (PR = 0.94), particularly near sleep onset. If the criterion for wakefulness is cognitive response to external stimulation, only in EEG Stages 3, 4, and REM can accurate distinctions between sleep and wakefulness be made. If EEG is the criterion, then the data suggest that cognitive response is possible during Stages 1 and 2 "sleep." The concept of a sleep onset period (SOP), characterized by lengthening response times and intermittent response failure (thereby reflecting neither true sleep or wakefulness), may provide a useful resolution of this definitional dilemma.

Effects of traffic noise on quality of sleep: assessment by EEG, subjective report, or performance the next day.

Twelve people living in areas of high traffic noise were studied to assess its effect on their sleep. During 3 weeks, their sleep was monitored physiologically in the natural setting of their own bedrooms. Their performance and subjective report of sleep were recorded each day. For the middle week, the bedroom windows were double glazed to reduce the prevailing level of traffic noise at the bedside [Leq 46.6 dB(A) over the whole night] by an average of 5.8 dB(A). Most physiological measures were unaffected by the noise reduction, but stage 4 sleep and low-frequency, high-amplitude delta waves in the EEG, both thought to be signs of deep sleep, were increased. Also unprepared simple reaction time, a test sensitive to drowsiness, was improved the next day, whereas a more stimulating short term memory test was not. Subjects also reported sleeping better. These improvements with double glazing were all modest in degree, but as they occurred in three independent and predicted measures of sleep quality, the view is supported that the prevailing level of traffic noise does indeed impair sleep.

Choice reaction time. A method of measuring postoperative psychomotor performance decrements.

Postoperative psychomotor performance changes were measured in three groups of thirteen subjects using a portable serial four-choice reaction time apparatus. Anaesthesia consisted of either thiopentone, nitrous oxide and halothane (thiopentone subjects) or methohexitone and fentanyl/nitrous oxide and incremental methohexitone (methohexitone subjects). Tests were performed on the day before operation and after 2, 4, 6, 8 and approximately 24 hours recovery on both groups of patients and at approximately the same times on nonoperated control patients. Control subjects' mean four-choice reaction time decreased steadily with practice such that the difference between first and last tests was statistically significant. Mean four-choice reaction times of thiopentone and methohexitone subjects increased from 515 to 550 ms and 552 to 600 ms respectively after 2 hours recovery. Subsequently four-choice reaction times decreased in both groups although methohexitone subjects were still significantly slower than controls after 6 hours. Thiopentone subjects were slower than controls at 2, 4 and 8 hours recovery. There was no difference between the three groups of subjects after 24 hours recovery.

Effects of sleep deprivation on signal detection measures of vigilance: implications for sleep function.

In an attempt to tease out the extent to which the performance decline during sleep deprivation might be due to a fall in the inherent capacity (d') of a subject, the parameters of the theory of signal detection were applied to auditory vigilance data obtained five times per 24 h during 60 h of continuous wakefulness. Eight subjects were exposed to both control and deprivation conditions in a balanced design. Oral temperature and self-assessed alert-drowsy reports were taken at three hourly intervals. The value of d' exhibited a significant stepwise decline during deprivation, falling sharply within the usual sleep period and levelling out during the daytime. Both temperature and self-assessment data exhibited clear circadian rhythms overlying the declines due to deprivation. The changes in d' were seen to be consistent with a brain "restitutive" role for sleep function.

The effects upon vigilance and reaction speed of the addition of ephedrine hydrochloride to chlorpheniramine maleate.

The addition of stimulant, ephedrine hydrochloride (15 mg), to the antihistamine, chlorpheniramine maleate (10 mg) is shown significantly to reduce the adverse drowsy effects of the latter upon various components of human performance. Auditory vigilance--a test of long-term attentiveness--is shown particularly to benefit from the addition of ephedrine. Whilst ephedrine does not aid simple reaction speed, it does reduce the pausing in serial-choice performance, indicative of a drowsy state, which otherwise occurs under chlorpheniramine alone.

An investigation of the acute behavioural effects of styrene on factory workers.

A group of men exposed to styrene in a factory building glass-fibre boats performed a series of behavioural tests at the beginning and end of their shift, and the results were compared with those of a referent group from the same factory. Changes in mood were noted in both groups of workers but were greater in the exposed men; moreover, the change in mood was correlated with blood styrene concentration. In the styrene workers the morning reaction time was slower than that for the referents. During the day the reaction time of the men with low blood styrene concentration (less than or equal to 5.4 mumol/l) speeded up and in the afternoon was similar to that of the referents; the reaction time for the men with high blood styrene concentration (greater than or equal to 5.5 mumol/l) was unchanged. Data taken from a questionnaire indicated that the men exposed were much more likely than was the referent group to report feeling unduly tired. They also reported feeling more tired on Friday night than Monday night, suggesting that the styrene might have a cumulative effect through the week.

A portable pulse-interval modulation telemetry/multiplexing EEG recording system for use in the home.

A portable 6-channel recording system employing time-division multiplexing with cable or radio-telemetry has been developed. The system is very compact and has proved to be reliable when used in a domestic environment. The use of multiplexing, in general, permits an expansion in the number of available channels and a reduction in equipment and tape costs, while the use of pulse interval modulation, in particular, overcomes tape recording limitations which may be encountered with the more common amplitude modulation techniques.

EEG event-related potentials and signal detection.

The purpose of this study was to determine whether certain previously reported relationships between event-related potentials and measures of signal detection performance occur in vigilance as well as psychophysical settings. In the course of the study, evidence was found which challenges previously proposed psychological correlates of "P300". EEG was recorded while 15 subjects carried out a 40-min signal detection test. CNV was measured between a warning click and the brief offset of a dim light denoting the possible (p = 0.5) occurrence of the signal, a faint tone in the constant background noise. P300 was measured at a point 300 msec following offset of the dim light. As reported previously in psychophysical settings, P300 amplitude was positively related to signal intensity and response confidence, and was larger for correct detections (Hits) than for correct rejections, misses or false alarms. From first to second half of the test both Hits and false alarms fell, response criterion beta rose, and the amplitude of both CNV and P300 fell. The latter negative relationship between beta and P300 contrasted with a positive one when subjects rated their signal reports at three levels of confidence; here the most confident ratings (high beta) were associated with the highest amplitude of P300. CNV reflected individual ability to sustain performance. Results are explained in terms of a two-factor version (Wilkinson, 1976) of the prior state/reactive change hypothesis (Karlin, 1970). It is suggested that time on task constitutes a prior state influence on P300, whereas other variables influence P300 by means of either reactive change or 'real' change in an endogenous P300 component.

Effects of sleep deprivation on short duration performance measures compared to the Wilkinson auditory vigilance task.

The effects of one night's total sleep deprivation were examined using the Wilkinson vigilance task and four 10 min duration performance tests. A repeated measures design was used in which eight male subjects experienced one night of sleep loss, the order of sleep loss being balanced across subjects. The four short duration performance tests consisted of choice reaction time, simple reaction time, short-term memory, and a motor task, handwriting. The results confirm the effects of one night's sleep deprivation on the vigilance task and also show that performance on the two reaction time tests was significantly impaired by the loss of sleep, but not at such a high level as for the vigilance. The short-term memory test failed to show any adverse effects of sleep loss and similarly for the handwriting. The experiment shows that two portable and brief (10 min) performance tests are sensitive indices of sleep loss and should be particularly useful for assessing levels of alertness in the field.