Saccadic eye movements estimate prolonged time awake.

Prolonged time awake increases the need to sleep. Sleep pressure increases sleepiness, impairs human alertness and performance and increases the probability of human errors and accidents. Human performance and alertness during waking hours are influenced by homeostatic sleep drive and the circadian rhythm. Cognitive functions, especially attentional ones, are vulnerable to circadian rhythm and increasing sleep drive. A reliable, objective and practical metrics for estimating sleepiness could therefore be valuable. Our aim is to study whether saccades measured with electro-oculography (EOG) outside the laboratory could be used to estimate the overall time awake without sleep of a person. The number of executed saccades was measured in 11 participants during an 8-min saccade task. The saccades were recorded outside the laboratory (Naval Academy, Bergen) using EOG every sixth hour until 54 hr of time awake. Measurements were carried out on two occasions separated by 10 weeks. Five participants participated in both measurement weeks. The number of saccades decreased during sustained wakefulness. The data correlated with the three-process model of alertness; performance differed between participants but was stable within individual participants. A mathematically monotonous relation between performance in the saccade task and time awake was seen after removing the circadian rhythm component from measured eye movement data. The results imply that saccades measured with EOG can be used as a time-awake metric outside the laboratory.

Contrast sensitivity and the effect of 60-hour sleep deprivation.

PURPOSE: The study aimed to evaluate the possible influence of prolonged sleep deprivation on achromatic and chromatic (red-green and blue-yellow) contrast sensitivity (CS). METHODS: During 60-hr sleep deprivation, CS was measured in 11 naval officers every sixth hour using videographic (Vigra-C) sine-wave-generated stimuli. RESULTS: When comparing the CS measurements obtained in the first and last 24 hr of the study, no statistically significant mean changes of achromatic CS (2.0, 5.9 and 11.8 cpd) or yellow-blue CS (0.6, 2.0 and 4.7 cpd) were found, while a significantly increased mean red-green CS at 2.0 and 4.7 cpd was recorded in the last 24 hr (p = 0.003 in both). The variance of achromatic and chromatic CS measurements in the group did not differ significantly in the first and last 24 hr test periods. CONCLUSIONS: Prolonged sleep deprivation does apparently not cause clinically or occupationally significant changes of contrast sensitivity in otherwise healthy subjects with normal visual acuity.

Improving the saccade peak velocity measurement for detecting fatigue.

The aim of the study was to compare saccadic peak velocity (SPV) values measured with video based Fitness Impairment Tester (FIT) and electro-oculography (EOG) during prolonged wakefulness. We tested different numbers of saccades and two saccade paradigms to improve the EOG measurements for detecting fatigue. The SPVs were measured from 11 fast patrol boat navigators with FIT and EOG every sixth hour until 54 h. Subjective sleepiness was assessed with the Karolinska Sleepiness Scale. EOG was measured using an overlap and a gap paradigm and the data was divided into sequential five 20-saccade blocks and cumulative blocks of 20, 40, 60, 80, and 100 saccades. Compared to the gap paradigm, the overlap paradigm produced a higher number of analyzable saccades for a given measurement time. The shorter measurements (20-40 saccades) appeared to be more sensitive for fatigue, whereas the longer measurements (60-100 saccades) were more sensitive to time spent on the task. Thus, the optimal number of saccades varies also depending on the research question. The EOG method was more sensitive to fatigue than FIT. The FIT values measured after 30 and 36 h of wakefulness did not differ significantly from the baseline values, while subjective sleepiness and the EOG values showed that the participants were significantly less alert at these time points. The EOG measurements can be improved for detecting fatigue by using the overlap saccade paradigm. The SPV values measured with the EOG method appear to be somewhat more sensitive in detecting fatigue than the FIT method.

Effects of 60 hours of total sleep deprivation on two methods of high-speed ship navigation.

This study investigated how workload and performance in high-speed ship navigation was affected by sleep deprivation using methods based on either paper charts or electronic chart display and information systems (ECDIS). In two separate weeks, five navigators sailed 10 routes in high-fidelity simulators while undergoing progressive sleep deprivation for up to 60 h. Results showed that navigation performance was better using ECDIS, but was largely unaffected by sleep deprivation in both. There was significant interaction between speed, sleep deprivation and navigation method, indicating that navigators using ECDIS reduced their speed more while sleepy. Secondary task performance was reduced by sleep deprivation, but was equally affected in both conditions. Workload was higher in the ECDIS condition, as indicated by subjective ratings and heart rate variability. No significant differences in sleepiness were found, but electroencephalographic recordings indicated more frequent microsleep episodes in the ECDIS condition. This may be influenced by lower overall arousal while navigating with ECDIS.

Effects of navigation method on workload and performance in simulated high-speed ship navigation.

This study examines mental workload and performance in simulated high-speed ship navigation. Two navigation methods were compared based on an electronic chart display and information system (ECDIS) and a conventional system using paper charts. Twenty naval cadets navigated in high-fidelity simulators through a 50 nautical mile course with varying levels of difficulty. Results showed that ECDIS navigation significantly improved course-keeping performance, but reduced the total amount of communication on the bridge. No differences were observed in subjective workload between groups. Heart rate variability and skin conductance measurements indicated higher workload in conventional navigation, but the differences between groups were not significant.

Effect of an intervention addressing working technique on the biomechanical load of the neck and shoulders among hairdressers.

The purpose of this study was to describe, and analyse the effect of an intervention on, the biomechanical workload in the neck and shoulder region of female hairdressers. Arm elevation was measured by inclinometers and muscular load of m. trapezius by electromyography. The intervention comprised working technique recommendations, e.g. to work with less elevated arms and more relaxed muscles. The subjects were randomised between two different intensity levels of the intervention, one with written information only and the other with additional personal follow-up. The effect of the intervention was evaluated after 1-2 months. The hairdressers worked with their arms elevated 60 degrees or more for approximately 13% of the total working time and 16% during the specific hairdressing tasks. The intervention group including personal follow-up instructions had a reduction in workload from 4.0% to 2.5% of hairdressing time with highly elevated right upper arm, i.e. above 90 degrees . No effect was detected on muscular load or neck and shoulder symptoms after the intervention.