Laboratory studies on the effects of temperature variations on drowsiness

Study on the effect of human sympathetic nerve cold stimulation to relieve driving fatigue based on order recurrence plot

Driving fatigue is very likely to cause traffic accidents, seriously threatening the lives and properties of drivers. Therefore, accurate detection and effective mitigation of driving fatigue are crucial for ensuring the personal safety of drivers. This study proposes a method to relieve driving fatigue by properly reducing the temperature to stimulate the human sympathetic nerve. The method uses the intelligent cooling and blowing device on the car seat cushion to achieve cold stimulation of the sympathetic nerve of the driver by reducing the temperature of the driver's hip, back and neck, so as to increase the excitement of the sympathetic nerve, keep the driver alert and achieve the purpose of fighting driving fatigue. In view of the fact that the traditional fatigue detection method is easily affected by environmental factors and individual differences, this study uses the order recurrence plot (ORP) method to detect driving fatigue based on electroencephalogram (EEG) signals. The results show that ORP textures drawn by EEG signals of the two driving conditions (normal driving condition and sensory cold stimulation driving condition) are significantly different, and the quantization parameters determinism (DET) and average diagonal line length (DLL) values are significantly different. Cold stimulation of the subjects' hips, back and neck to alleviate driving fatigue was the best when the temperature was 21 °C. In addition, compared with the traditional methods of fatigue relief, the sensory cold stimulation method proposed in this study does not easily to produce tolerance and has no damage to the body.

Mitigating passive fatigue during monotonous drives with thermal stimuli: Insights into the effect of different stimulation durations

Driving on monotonous roads has been shown to cause passive fatigue as even non-sleep-deprived drivers suffer from the lack of stimuli. Consequently, alertness is reduced and the risk of accidents increases. To counteract this risk, measures need to be taken to mitigate driver fatigue. While in the past, some studies have been focused on the potential of thermal stimuli to reduce fatigue, their results seem inconclusive. Examining the study conditions in which the thermal stimuli were studied, it becomes obvious that the duration of the thermal stimulus strongly affects perceived fatigue. To better understand this relation, a driving simulator study (n=33) was conducted investigating both a 2min and a 4min thermal stimulus (15öC), where air was circulated on non-sleep-deprived drivers. For the 4min stimulus, patterns of increased sympathetic activity (i.e. significant pupil dilatation and bradycardia) were recorded. Furthermore, participants subjectively rated fatigue significantly lower when the stimuli were applied, and preferred driving with the stimulus. The superior performance of the 4min stimulus can be derived from a longer effect on the physiological data as well as even lower subjective fatigue ratings. Results also point to the limits of thermal stimulation: 6min after the stimuli, the participants no longer feel an effect (based on subjective ratings). Future research on passive fatigue countermeasures should hence build on the identified effect of a 4min cooling stimulus to increase physiological arousal and focus on the opportunities to increase effect duration.

Psychophysiological responses to short-term cooling during a simulated monotonous driving task

For drivers on monotonous routes, cognitive fatigue causes discomfort and poses an important risk for traffic safety. Countermeasures against this type of fatigue are required and thermal stimulation is one intervention method. Surprisingly, there are hardly studies available to measure the effect of cooling while driving. Hence, to better understand the effect of short-term cooling on the perceived sleepiness of car drivers, a driving simulator study (n = 34) was conducted in which physiological and vehicular data during cooling and control conditions were compared. The evaluation of the study showed that cooling applied during a monotonous drive increased the alertness of the car driver. The sleepiness rankings were significantly lower for the cooling condition. Furthermore, the significant pupillary and electrodermal responses were physiological indicators for increased sympathetic activation. In addition, during cooling a better driving performance was observed. In conclusion, the study shows generally that cooling has a positive short-term effect on drivers' wakefulness; in detail, a cooling period of 3 min delivers best results.

Meteorologic factors and subjective sleep continuity: a preliminary evaluation

Little research has been undertaken to evaluate whether environmental factors other than bright light influence the individual's ability to initiate and maintain sleep. In the present analyses, nine meteorologic variables were evaluated for their possible relationship to self-reported sleep continuity in a sample of 43 subjects over a period of 105 days. In this preliminary analysis, high barometric pressure, low precipitation, and lower temperatures were significantly correlated with good sleep continuity. Interestingly, ambient light and lunar phase were not found to be strongly associated sleep diary measures.

Use of temperature variations to combat drivers' drowsiness

The purpose of the present study was to evaluate the efficiency of temperature variations as a measure against drivers' drowsiness. A system for regulation of the air temperature in the cab was installed in two trucks. Irregular temperature reductions of about 8 degrees C were introduced. The periods between the temperature reductions varied among 5, 6, 7, and 8 min. The periods for the temperature reductions varied between 2, 4, 6, and 8 min. The system was tested with 6 drivers on 54 trips. The system was applied for periods varying between 30 to 300 min. Changes in wakefulness were analysed using subjective ratings by the lorry drivers. The application of the system significantly improved subjectively rated wakefulness. The wakefulness was rated with a questionnaire completed after 10 min. use of a cooling system and at the end of its use. Analysis showed individual differences in the usefulness of the system: 3 of the 6 truck drivers reported positive reactions to the use of the temperature cooling system.

Onset of drowsiness and satiation after meals with different energy contents

The investigation consisted of a laboratory study with 10 healthy subjects who were both sleep and food deprived prior to each experimental condition. The aim of the study was to investigate the importance of energy content and the bulk of food on wakefulness and satiation. Each subject was tested in four conditions, each with equal food composition but different energy amounts: 100, 500 and 1000 kcal and 100 kcal with low bulk content. Recordings and ratings of wakefulness and satiations were carried out throughout the investigation, starting 30 minutes before and continuing until 90 minutes after intake of the food alternatives. No differences in wakefulness could be observed after the four food alternatives. However, subjects rated themselves as more satiated after the food alternatives with higher energy content and higher bulk.

Field studies on the effects of food content on wakefulness

The investigation included six drivers engaged in day driving and six drivers engaged in night driving. Changes in wakefulness were analysed by means of a questionnaire where the drivers were asked to rate their wakefulness on a 100 mm rating scale. Changes in wakefulness were analysed during intake of food with higher and lower contents of fat. The day-drivers had their intakes as breakfast and lunch, the night-drivers as dinner and between meals. No significant difference was observed between the two types of intake, meaning that the balance between fat, protein and carbohydrate does not effect the development of drowsiness.