Subjective sleepiness, simulated driving performance and blink duration: Examining individual differences. J Sleep Res 15: 47-53

National Institute for Psychosocial Medicine, Stockholm, Sweden.
Journal of Sleep Research (Impact Factor: 2.95). 03/2006; 15(1):47-53. DOI: 10.1111/j.1365-2869.2006.00504.x
Source: PubMed

ABSTRACT The present study aimed to provide subject-specific estimates of the relation between subjective sleepiness measured with the Karolinska Sleepiness Scale (KSS) and blink duration (BLINKD) and lane drifting calculated as the standard deviation of the lateral position (SDLAT) in a high-fidelity moving base driving simulator. Five male and five female shift workers were recruited to participate in a 2-h drive (08:00-10:00 hours) after a normal night sleep and after working a night shift. Subjective sleepiness was rated on the KSS in 5-min intervals during the drive, electro-occulogram (EOG) was measured continuously to calculate BLINKD, and SDLAT was collected from the simulator. A mixed model anova showed a significant (P < 0.001) effect of the KSS for both dependent variables. A test for a quadratic trend suggests a curvilinear effect with a steeper increase at high KSS levels for both SDLAT (P < 0.001) and BLINKD (P = 0.003). Large individual differences were observed for the intercept (P < 0.001), suggesting that subjects differed in their overall driving performance and blink duration independent of sleepiness levels. The results have implications for any application that needs prediction at the subject level (e.g. driver fatigue warning systems) as well as for research design and the interpretation of group average data.

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    • "It was concluded that there was always awareness of sleepiness before line crossings. In the previously mentioned simulator study (Ingre et al., 2006), the risk of line crossings with four wheels was increased 28 times at KSS = 8 and 185 times at KSS = 9, compared to the risk at KSS = 5. "
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    ABSTRACT: The main consequence of insufficient sleep is sleepiness. While measures of sleep latency, continuous encephalographical/electro-oculographical (EEG/EOG) recording and performance tests are useful indicators of sleepiness in the laboratory and clinic, they are not easily implemented in large, real-life field studies. Subjective ratings of sleepiness, which are easily applied and unobtrusive, are an alternative, but whether they measure sleepiness sensitively, reliably and validly remains uncertain. This review brings together research relevant to these issues. It is focused on the Karolinska Sleepiness Scale (KSS), which is a nine-point Likert-type scale. The diurnal pattern of sleepiness is U-shaped, with high KSS values in the morning and late evening, and with great stability across years. KSS values increase sensitively during acute total and repeated partial sleep deprivation and night work, including night driving. The effect sizes range between 1.5 and 3. The relation to driving performance or EEG/EOG indicators of sleepiness is highly significant, strongly curvilinear and consistent across individuals. High (>6) KSS values are associated particularly with impaired driving performance and sleep intrusions in the EEG. KSS values are also increased in many clinical conditions such as sleep apnea, depression and burnout. The context has a strong influence on KSS ratings. Thus, physical activity, social interaction and light exposure will reduce KSS values by 1–2 units. In contrast, time-on-task in a monotonous context will increase KSS values by 1–2 units. In summary, subjective ratings of sleepiness as described here is as sensitive and valid an indicator of sleepiness as objective measures, and particularly suitable for field studies.
    Journal of Sleep Research 04/2014; 23(3). DOI:10.1111/jsr.12158 · 2.95 Impact Factor
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    • "The frequency of blinks may increase or decrease as participants become more sleepy (Stern et al., 1984) and is consequently not useful for measuring sleepiness. In contrast, the duration of blinks has been found to increase in several studies (Caffier et al., 2003; Ingre et al., 2006; Schleicher et al., 2008). The increase is primarily due to a slower opening phase, but the closing phase increases as well (Lobb and Stern, 1986). "
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    ABSTRACT: Driver sleepiness contributes to a considerable proportion of road accidents, and a fit-for-duty test able to measure a driver’s sleepiness level might improve traffic safety. The aim of this study was to develop a fit-for-duty test based on eye movement measurements and on the sleep/wake predictor model (SWP, which predicts the sleepiness level) and evaluate the ability to predict severe sleepiness during real road driving. Twenty-four drivers participated in an experimental study which took place partly in the laboratory, where the fit-for-duty data were acquired, and partly on the road, where the drivers sleepiness was assessed. A series of four measurements were conducted over a 24-h period during different stages of sleepiness. Two separate analyses were performed; a variance analysis and a feature selection followed by classification analysis. In the first analysis it was found that the SWP and several eye movement features involving anti-saccades, pro-saccades, smooth pursuit, pupillometry and fixation stability varied significantly with different stages of sleep deprivation. In the second analysis, a feature set was determined based on floating forward selection. The correlation coefficient between a linear combination of the acquired features and subjective sleepiness (Karolinska sleepiness scale, KSS) was found to be R = 0.73 and the correct classification rate of drivers who reached high levels of sleepiness (KSS ⩾ 8) in the subsequent driving session was 82.4% (sensitivity = 80.0%, specificity = 84.2% and AUC = 0.86). Future improvements of a fit-for-duty test should focus on how to account for individual differences and situational/contextual factors in the test, and whether it is possible to maintain high sensitive/specificity with a shorter test that can be used in a real-life environment, e.g. on professional drivers.
    Transportation Research Part C Emerging Technologies 01/2013; 26:20-32. DOI:10.1016/j.trc.2012.07.008 · 2.01 Impact Factor
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    • "Administration of a (typhoid) vaccine that causes an increase in interleukin (IL)-6 levels is paralleled by increased fatigue (Harrison et al., 2009). Along the same lines, observational studies show that low-grade inflammation is related to poor subjective health (Christian et al., 2011; Lekander et al., 2004), in which short or poor sleep is an important factor (Ingre et al., 2008; Singh-Manoux et al., 2006; Steptoe et al., 2006). Sleep-related sickness behaviour is believed to have evolved to conserve energy in order to increase recuperation (Dantzer et al., 2008). "
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    ABSTRACT: Sleepiness is linked to accidents and reduced performance, and is usually attributed to short/poor prior sleep and sleepiness. However, while the link between reduced sleep and subsequent sleepiness is well established in laboratory experiments of sleep reduction, very little is known about the day-to-day variation of sleepiness in everyday life and its relation to the immediately preceding sleep episode. The purpose of the present study was to investigate the characteristics of this relation across 42 consecutive days. Fifty volunteers participated. Self-reports of sleep were given in the morning and recorded with actigraphy; health was rated in the evening; and sleepiness was rated at eight points during the day (on a scale of 1-9). Results from mixed-model regression analyses showed that, on average, total sleep time predicted sleepiness during the rest of the day across the 42 days, with sleepiness increasing with shorter preceding sleep (β = -0.15 units h(-1) , P < 0.001). Sleepiness also increased with earlier time of rising and lower-rated sleep quality. Days off reduced sleepiness, but was accounted for by sleep. Self-rated health improved when sleepiness was low during the same day (β = -0.36 unit unit(-1) of rated health, P < 0.001), but the two were measured simultaneously. Napping was related to high sleepiness during the same day. Actigraphy measures of sleep duration showed similar, but somewhat weaker, effects than diary measures. It was concluded that the main determinants of daytime sleepiness in a real-life day-to-day context were short sleep, poor sleep and early rising, and that days with high sleepiness ended with ratings of poorer health.
    Journal of Sleep Research 12/2012; 22. DOI:10.1111/jsr.12014 · 2.95 Impact Factor
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