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nineteenth century, Samuel Taylor Coleridge gave us this verse: Oh. Sleep!It is a gentlething,. Belovedfrompole to pole. Unquestionably, during the last few ...
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SLEEP DEPRIVATION Clinical Issues, Pharmacology, and Sleep Loss Effects

ADDITIONAL VOLUMES IN PREPARATION

Clete A. Kushida

Long-Term Intervention in Chronic Obstructive Pulmonary Disease, edited by R. Pauwels, D. S. Postma, and S. T. Weiss

Stanford University Stanford, California

Pneumocystis Pneumonia: Third Edition, Revised and Expanded, edited by P. D. Walzer and M. Cushion Ion Channels in the Pulmonary Vasculature, edited by J. x.-J. Yuan Asthma Prevention, edited by ~

~ Busse and R. F. Lemanske, Jr.

The opinions expressed in these volumes do not necessarily represent the views of the National Institutes of Health.

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Introduction

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The second half of the past century was a time of remarkable scientific expansion and knowledge explosion. Biology and health fields were the beneficiaries of many genuine observations and discoveries and, as a result, the health of individuals and the public as a whole improved markedly. The area of sleep and sleep disorders illustrates the advances in knowledge that occurred. Sleep is a topic that has long been addressed by writers-but much more frequently by poets than by researchers. As an example, in the beginning of the nineteenth century, Samuel Taylor Coleridge gave us this verse: Oh. Sleep!It is a gentlething, Belovedfrompole to pole

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Unquestionably, during the last few decades the study of sleep and its biology in health and disease has moved to the forefront of research, and it has revealed a wealth of observations. At the same time, it has attracted the interest of many investigators with expertise in diverse basic disciplines and clinical areas. The association of sleep disorders with other clinical fields such as cardiology, neurology, mood and attention disorders, and pneumology is well recognized. Sleep deprivation is a medical issue. but also a social one. As a consequence, we have seen a number of societal and regulatory changes to ensure tht nnrnn,.;"tp

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13 Impact on Self-reported Sleepiness, Performance, Effort, and Motivation

JUNE J. PILCHER AND HEATHER N. ODLE-DUSSEAU Clemson University, Clemson, South Carolina, U.S.A.

I.

Introduction

Sleep deprivation commonly occurs in a variety of situations in modern society. Shift work, especially night work, often results in chronic partial sleep deprivation. Furthermore, some segments of modem society, such as high-school and college students, voluntarily deprive themselves of sleep due to work, school, and social obligations (1,2). In addition, some segments of the population in such jobs as emergency services, medical care, and the military experience total sleep deprivation of 24 hr or more on a regular basis (3). In spite of the prevalence of partial and total sleep deprivation in our society, however, there remain many unanswered questions about the effects of sleep deprivation on human functioning. Many studies have examined the effects of sleep deprivation on performance (e.g., Refs. 4-10). Narrative reviews of these and many other sleep deprivation studies have concluded that sleep deprivation negatively affects performance but that the extent of the decrement depends on the type of performance task, the length of the task, and the rate at which the task must be completed (11-14). Furthermore, two meta-analytic reviews examining the effect of sleep deprivation on performance resulted in similar conclusions (15,16). Unfortunately, the effects of sleep deprivation on subjective experiences or verbal reports are much less well understood. The potential effect of sleep depri?'il

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vation on subjective reports is an important consideration in the field. An individual's subjective assessment of the effects of sleep deprivation provides insight into that individual's knowledge of his or her limits under sleep deprivation conditions, which could, in turn, impact the individual's effort or decision-making capability. For example, shift workers who often live under partial sleep deprivation conditions, and at times total sleep deprivation conditions, must constantly assess their ability to function adequately to carry out their work. This self-assessment could in turn impact the decision-making process where the worker chooses to engage in relatively safe behavior or relatively unsafe behavior while on the job. In other words, if a worker accurately recognizes that his performance is decreased, the worker may logically reduce risk-taking behaviors on the job and thus decrease the likelihood of an accident. On the other hand, if a worker overestimates the effect of sleep deprivation on his performance, he may choose to operate slower or less efficiently in an effort to compensate when no compensation may actually be necessary. Although a variety of self-report methods have been developed for and used in research in other areas such as memory, decision making, educational psychology, instruction, and clinical psychology (17,18), they have yet to be fully implemented in research on sleep deprivation. The purpose of this chapter is to examine the literature on verbal reports in sleep deprivation and to discuss future directions of research in the sleep deprivation field using verbal reports.

II. Subjective Sleepiness Perhaps the most common type of verbal report used in sleep deprivation studies is a measure of subjective sleepiness. Subjective sleepiness is generally assessed by self-report scales (see also Chap. 1), such as the Stanford Sleepiness Scale (19), the Epworth Sleepiness Scale (20), visual analog scales (21), and the vigor and fatigue subscales on the Profile of Mood States (pOMS; Educational and Industrial Testing Service, San Diego, CA). These measures have been used in studies on the effects of sleep deprivation (22-25), shift work (26-28), and sleep disorders (29,30). Assessing subjective sleepiness is an important issue in our 24n society. For instance, workers frequently have to rely on their internal assessment of sleepiness when making decisions about whether they are alert enough to work an extra shift or drive a little further before stopping. Often the subjective feeling of sleepiness may be one of the first cues that a worker has that he or she can no longer function on the job in a safe manner. Obviously this type of self-assessment can have profound safety implications in real-world settings. A number of studies have investigated subjective sleepiness under sleep deprivation conditions. A study on the effects of partial sleep deprivation found that subjective sleepiness increased as the sleep deprivation period progressed across 5 consecutive days (31). Other studies have also found that sleepiness increased during different lengths of sleep deprivation and varied by time of day,

, tI

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with greater sleepiness reported at night (32). A similar time-of-day effect on subjective sleepiness has been shown in real-work conditions, such as in locomotive engineers, many of whom work under on-call work schedules (33). Subjective sleepiness has also been studied as a potential predictor of task performance when sleep-deprived. Glenville and Broughton (34) reported that subjective sleepiness was significantly correlated with performance on tasks that produced deficits under sleep deprivation conditions. A follow-up study indicated that sleepiness was correlated more strongly with reaction time, the task that showed the greatest decrement under sleep deprivation (31). Based on these results, the authors concluded that subjective sleepiness may best predict performance for those tasks that result in considerably reduced performance efficiency. In contrast, another set of studies found that subjective ratings of sleepiness were only marginally related to performance (35,36). In an effort to contribute to this issue, Gillberg and colleagues (23) completed a study that examined the relationship between sleepiness and performance but specifically controlled for factors they felt could influence sleepiness, such as prior sleep duration and circadian phase. They found that subjective sleepiness was correlated with performance on a vigilance task. The data summarized here indicate that, as would be expected, subjective sleepiness is related to the amount of sleep loss. The relationship of subjective sleepiness to performance under sleep deprivation conditions, however, is less well understood. This is especially true when considering that much of the recent research on examining subjective sleepiness and performance has been completed on vigilance-type tasks. Work-related tasks involve a much wider range of tasks, of which vigilance may be only one small part. Research investigating the relationships between subjective sleepiness and a variety of tasks ranging from simple reaction time to more complex cognitive tasks and decision-making tasks is still needed. III. Self-monitoring Performance The relationship between subjective sleepiness and performance is only one method of examining potential relationships between how individuals perceive the effects of sleep deprivation on their ability to function. Another method is to examine how capable sleep-deprived individuals are of self-monitoring their level of performance. As with subjective sleepiness, the ability to accurately monitor performance under sleep-deprived conditions is an important issue for many workers in our society.Unfortunately, few studies have addressed this particular topic. Historically, the literature examining self-monitoring of perfornlance has led to two areas of research. One line of research has examined confidence in rating andjudgment accuracy in response to performance on different types of tasks (e.g., Refs. 37,38). The second line of research has focused on the relationship between confidence assessment of performance and actual performance (39,40).

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This second line of research is a type of calibration research (41), where participants complete a task multiple times, provide an assessmentof how well they did, and provide a rating of how certain they feel of their judgment. Although much of the research in the sleep deprivation field on self-monitoring performance has not specifically addressed the issue in regard to these two methodological approaches, the methods used can be classified into the two categories. Some studies have examined self-monitoring of performance on a task after a period of sleep deprivation while others have examined self-monitoring of performance on repeated tasks during the sleep deprivation period. However, the results from these studies were inconsistent. For example, one study asked doctors to answer a series of medically related questions after a night of on-call duty and after each question had them rate how certain.theywere that their answer was correct (42). This study concluded that although the doctors performed worse, they could accurately assess their performance. Similarly,another study indicated that sleep-deprived persons reported lower confidence in their incorrect responses to cognitive reasoning tasks (43). Dorrian and colleagues (44) asked sleepdeprived individuals to assess their performance on six different tasks that were repeated during the sleep deprivation period and found that self-ratings of performance were moderately to highly correlated with actual performance. In another study, college students were kept awake for one night and then asked to complete a complex linguistic task and assess their performance (45). This study concluded that the students performed worse, but overestimated their performance on the task. In contrast, two other studies examining self-monitoring of performance on tasks repeated during the night concluded that the individuals could accurately assess their performance ability (46,47). One possible explanation for the different conclusions from these studies could be that some studies used a one-time performance assessment while others used a repeated performance assessment. However, this does not account for all differences since some studies used the same basic method, yet found different results. Another explanation could be the type of tasks used. Studies in the calibration research area have found that subjects have the tendency to overestimate their performance on difficult tasks but underestimate their performance on simple tasks, a phenomenon called the calibration difficulty effect (48,49). Although research in the sleep deprivation field has not specifically addressed the calibration difficulty effect, it is possible that it could apply to the reported results. For example, the tasks completed by the doctors (42) ranged in difficulty so that they could have been overestimating their performance on some tasks and underestimating their performance on others. The college students (45) completed a task that was cognitively challenging and, accordingto the calibration difficulty effect, should have overestimated their performance. Dorrian and colleagues (44) used several fairly simple vigilance and reaction time tasks and a more difficult grammatical reasoning task. Thus, it is possible that the type of task used was related to the strength of the correlation between self-rated performance and actual performance reported in their study.

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Another aspect of self-monitoring performance while sleep-deprived is the ability to anticipate performance through prospectite estimates in addition to correctly assessing performance through retrospective self-monitoring. Dorrian and colleagues (44) addressed this issue in their study and found moderate correlations between predicted performance scores and actual performance scores. However,they noted that the posttest self-ratings were better related to actual performance than the pretest ratings. Unfortunately, few studies have examined the effect of sleep deprivation on self-monitoring of performance ability. Many questions still need to be addressed in this area. One potential research question involves whether the type of task is related to the ability to monitor performance. This could be particularly important when applying research results to a work setting in that many work settings require a wide range of tasks, some that may be quite easy and some that may require quick but complex judgment calls. Another potential research area is how and when performance is required. In other words, is peifol7nallce assessed during the sleep deprivation period to simulate a night shift or is pelformonce assessed the next day to simulate peifonnance during the day after sleep deprivation the previous night? Finally, another area of research that has not been well investigated is the ability of a sleep-deprived individual to accurately predict hislher ability to perform a task, something that all workers must do on a regular basis while on the job.

IV. Subjective Effort Another variable that can impact the effect of sleep deprivation on performance is the amount of effort that the individual devotes to completing the task. A number of researchers have speculated that sleep deprivation negatively affects performance largely through "resource limiting" (11,50) in that the sleep-deprived individuals may decrease their effort to perform as sleep deprivation progresses. Some researchers have supported the supposition that sleep deprivation can negatively affect the willingness of the subject to put forth the effort necessary to successfully complete a task (51). In contrast, other researchers have proposed that sleep-deprived individuals may actually realize that their perfoffilance is decremented and may increase their effort to compensate (44). Thus, the relationship between sleep deprivation and effort on task is another imp011antcomponent of understanding how sleep deprivation affects our ability to perform. One means of examining the effect of sleep deprivation on effort is to ask sleep-deprived individuals to estimate how much effort they put into a task that they just completed. Although several sleep deprivation studies have used this approach, the results remains unclear. Some studies have reported decreased performance but increased effort on cognitive tasks (45), while other studies have seen an increased effort associated with no change in performance (52,53). Yet another study examining effort on cognitive tasks found no change in

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reported effort (54). Studies have also examined effort in relation to physical performance after sleep deprivation and have reported an increase in subjective effort (55,56). Another means that researchers have used to examine effort is to allow individuals to choose between high-effort and low-efforttasks (57,58). Unfortunately, only a few studies have examined the effect of sleep deprivation on effort in this manner and compared the results to subjective effort. One study examining the effect of sleep deprivation on a chosen amount of exercise reported that exercise level was the same in sleep-deprived and non-sleep-deprived conditions but that self-reported effort in the sleep-deprived conditions was increased (59). In contrast, another study allowed individuals to match perceived effort when sleepdeprived with perceived effort after normal sleep conditions by increasing the incline on a treadmill and found that there was no change in the physical requirements chosen between the two conditions (60).A study by Legg and Haslam (61) reported similar results. They used an industrial repetitive lifting task to determine the chosen maximum lifting load under normal sleep and sleep deprivation conditions and concluded that there was no difference. In one study that allowed sleep-deprived individuals to choose complexity levels on a cognitive task (62), the participants chose less-demanding problems than individuals with no sleep loss but reported similar levels of subjective effort. Although some research has been devoted to the relationship between performance and subjective effort in sleep-deprived individuals, many questions remain unanswered. More studies are needed that examine self-report effort on a variety of tasks to better understand how effort and sleep deprivation may interact in the typical work environment. In addition, more studies are needed that provide sleep-deprived individuals the chance to choose what tasks to complete, a situation that is common in many work settings. Results from studies such as these would allow for greater applicability from the basic research to the applied setting. V.

Subjective

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conditions (65,66). Offering other types of external sources of motivation has also proven to have a positive effect on performance under sleep deprivation conditions. For example, Horne and Pettitt (67) offered a significant monetary reward for correct responses and found that participants were capable of maintaining baseline performance levels for up to 36 hr of sleep deprivation. Of interest for this chapter, however, is the ability of individuals to accurately assess their internal state of motivation during sleep deprivation conditions. Unfortunately, research in the sleep deprivation field has not yet addressed this issue. It would seem that questions assessing individuals' motivation to complete a task might be related to, yet different from, their subjective assessment of effort. Future studies could be designed to investigate the relationship between sleep deprivation and motivation to complete a task and the relationship of motivation to subjective effort.

VI. Conclusions Although the effects of sleep deprivation have been investigated quite thoroughly over the years, some aspects of sleep deprivation are not well understood. Some of the least-well-understood effects of sleep deprivation are the subjective aspects that have been summarized in this chapter. Although some research has been completed on topics such as subjective sleepiness, there remain quite a number of questions to be addressed especially in areas concerning performance when sleep-deprived. More research is needed on how subjective assessments of sleepiness are related to performance and on effort and motivation when sleepdeprived. Additional research is also needed to address the ability of sleep-deprived individuals to predict their performance before completing a task as well as estimate their performance after completing a task. Although these types of self-assessment questions can be difficult to answer because of the very nature of self-reported data, they are nonetheless worthy of well-thought-out and well designed research projects.

Motivation

An area of research in the sleep deprivation field that is closely tied in with effort to perfonn well is motivation. The more sleep-deprived individuals become, it seems intuitively obvious that they will be less fully committed to performing well on tasks, particularly demanding tasks (63). However, this disinclination to perform can be overcome, at least to some extent, through external sources of motivation. One means of encouraging motivation is to provide information about performance while completing a task, what is known as knowledge of results. Wilkinson (64) was one of the first researchers to point out the positive effect of knowledge of results on performance. More recent studies have also supported the positive effect of knowledge of results on performance in sleep deprivation

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14 Driving Performance

PIERRE PHILIP AND JACQUES TAILLARD Clinlque du Sommeil Chu Bordeaux, Bordeaux, France

I. Introduction Traffic is rapidly increasing in all developed countries. In 1998, road traffic injuries were globally estimated to be then ninth leading cause of loss of healthy life and are projected to become the third leading cause by 2020 (1). This increase is associated with a major concern about safety from the traffic authorities. Several risk factors are now well identified (i.e., alcohol, speed) but sleepiness is still a concern in many countries. If excessive somnolence at the wheel is thought to be an important cause of accidents in modern societies, the most important ways that sleepiness contributes to these accidents are still poorly understood. Sleepiness can be related to behavioral, pathological or pharmacological causes. This chapter will describe successive epidemiological studies that first highlighted the problem of sleepiness and driving. We will then consider the different methods developed by researchers to quantify driving impairment. The relationship between sleep schedules, organic sleep disorders, central nervous system drugs, and accidents will be reviewed. Finally, the impact of treatment in patients and the impact of countermeasures in healthy subjects on driving skills will be disclosed.

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