The psychophysiology of driver fatigue/drowsiness : electroencephalography, electro-oculogram, electrocardiogram and psychological effects

University of Technology, Sydney. Faculty of Science.Driver fatigue is a major cause of road accidents and has implications for road safety. Investigating the psychophysiological links to fatigue can enhance our understanding and management of fatigue in the transport industry. A variety of psychophysiological parameters have been identified as indicators of fatigue, with electroencephalography (EEG) perhaps being the most promising. Therefore, monitoring EEG during driver fatigue may be a promising variable for use in fatigue countermeasure devices. However, most previous fatigue-based studies have suffered from methodological shortcomings such as insufficient sample numbers, lack of a controlled testing environment, inadequate study design and statistical analysis. Furthermore, a thorough psychophysiological assessment of fatigue was found to be lacking in the literature. Therefore, the aims of the present doctoral research were to: 1) Assess the EEG and electro-occulogram (EOG) changes during driver fatigue in a 'state of the art' experimentally controlled study. 2) Identify psychological associations with fatigue. 3) Assess the changes in autonomic nervous system activity during fatigue. 4) Investigate the differences in the physiological changes that occur during fatigue in professional versus non-professional drivers. 5) Identify the reproducibility of physiological changes that occur during fatigue. 6) Examine the changes in EEG coherence during fatigue. 7) Utilise the physiological findings in this research for the development of EEG based software to detect fatigue. The results showed significant increases in delta and theta during driver fatigue. The conventional high amplitude blinks during alertness was replaced with slow, low amplitude blinks during fatigue. Reduced Fatigue-Inertia and decreased VigourActivity (which are mood sub-scales) and increased anxiety levels were associated with fatigue. There was an increase in parasympathetic activity during fatigue. Nonprofessional drivers showed greater increases in the EEG of fatigue compared to professional drivers. The EEG changes associated with fatigue were shown to be reproducible. The changes in EEG coherence were not found to be significant during fatigue. The EEG changes during fatigue were used for the development of an algorithm for a fatigue-countermeasure device and was shown to reliably detect fatigue. In summary, this research has provided important information on the psychophysiology of driver fatigue clarifying some of the findings of prior research. Significant changes were found to occur in EEG, EOG and parasympathetic activity during fatigue. From this research it may also be suggested that psychological status of the driver may influence fatigue status. Furthermore, the EEG changes during fatigue are consistent and reliable, which can be utilised to detect fatigue in a EEG-based fatigue countermeasure device. The results are discussed in the light of direction for future driver fatigue studies and fatigue management

Electroencephalography activity associated with driver fatigue: Implications for a fatigue countermeasure device

This paper reviews the association between electroencephalography (EEG) activity and driver fatigue. The current literature shows substantial evidence of changes in brain wave activity, such as simultaneous changes in slow-wave activity (e.g., delta and theta activity) as well as alpha activity during driver fatigue. It is apparent from the literature review that EEG is a promising neurophysiological indicator of driver fatigue and has the potential to be incorporated into the development of a fatigue countermeasure device. The findings from this review are discussed in the light of directions for future fatigue research studies

A critical review of the psychophysiology of driver fatigue

Driver fatigue is a major cause of road accidents and has implications for road safety. This review discusses the concepts of fatigue and provides a summary on psychophysiological associations with driver fatigue. A variety of psychophysiological parameters have been used in previous research as indicators of fatigue, with electroencephalography perhaps being the most promising. Most research found changes in theta and delta activity to be strongly linked to transition to fatigue. Therefore, monitoring electroencephalography during driver fatigue may be a promising variable for use in fatigue countermeasure devices. The review also identified anxiety and mood states as factors that may possibly affect driver fatigue. Furthermore, personality and temperament may also influence fatigue. Given the above, understanding the psychology of fatigue may lead to better fatigue management. The findings from this review are discussed in the light of directions for future studies and for the development of fatigue countermeasures. Copyright © 2001 Elsevier Science B.V

Driver fatigue: Electroencephalography and psychological assessment

Fatigue has major implications for transportation system safety; therefore, investigating the psychophysiological links to fatigue could enhance our understanding and management of fatigue in the transport industry. This study examined the psychophysiological changes that occurred during a driver simulator task in 35 randomly selected subjects. Results showed that significant electroencephalographic changes occur during fatigue. Delta and theta activity were found to increase significantly during fatigue. Heart rate was significantly lower after the driving task. Blink rate also changed during the fatigue task. Increased trait anxiety, tension-anxiety, fatigue-inertia and reduced vigor-activity were shown to be associated with neurophysiological indicators of fatigue such as increased delta and theta activity. The results are discussed in light of directions for future studies and for the development of a fatigue countermeasure device

Reproducibility of the spectral components of the electroencephalogram during driver fatigue

To date, no study has tested the reproducibility of EEG changes that occur during driver fatigue. For the EEG changes to be useful in the development of a fatigue countermeasure device the EEG response during each onset period of fatigue in individuals needs to be reproducible. It should be noted that fatigue during driving is not a continuous process but consists of successive episodes of 'microsleeps' where the subject may go in and out of a fatigue state. The aim of the present study was to investigate the reproducibility of fatigue during driving in both professional and non-professional drivers. Thirty five non-professional drivers and twenty professional drivers were tested during two separate sessions of a driver simulator task. EEG, EOG and behavioural measurements of fatigue were obtained during the driving task. Results The results showed high reproducibility for the delta and theta bands (r>0.95) in both groups of drivers. The results are discussed in light of implications for future studies and for the development of an EEG based fatigue countermeasure device. © 2004 Elsevier B.V. All rights reserved

The effect of home training with direct blood pressure biofeedback of hypertensives: A placebo-controlled study

Background. Home training in self-lowering of blood pressure using continuous blood pressure feedback has not previously been reported. Enhancement of laboratory-learned skills was hypothesized on the basis of outcomes from other intellectual, emotional and physical endeavours. Objective. To examine the supplementary effect of home blood pressure biofeedback training. Design. Thirty unmedicated, mild hypertensives participated in a randomized, double-blinded, modified contingency placebo-controlled study. Method. After suitable screening and baseline blood pressure measurements subjects undertook eight laboratory biofeedback sessions and then 12 home training sessions over 4 weeks using continuous finger blood pressure monitoring. Results. In the laboratory those being administered active therapy (n =16) lowered systolic pressures by 5 ± 5.4 mmHg compared with a lowering of 4 ± 4.2 mmHg with placebo (NS). During the fourth week at home lowering for the active group (11 ± 8 mmHg) was greater than that with placebo (4 ± 6.2 mmHg, P = 0.017). Arm-cuff blood pressures were not statistically different for groups and with time but that of the active group was lower by 9 ± 15.4/7 ± 10.2 mmHg, which is a clinically relevant change, after home biofeedback. Conclusions. The efficacy of self-lowering of systolic blood pressure in mild hypertensives by continuous feedback was enhanced by 6 mmHg with 4 weeks of practice at home. Standard arm-cuff blood pressure was reduced by a clinically relevant amount. The home environment proved cost effective for this 'high-tech' approach

Optical flow image analysis of facial expressions of human emotion - Forensic applications

© 2008 ICST. The objective of this study was to induce emotions in individuals to determine if specific facial movements could be detected and analysed by the optical flow technique. This analysis is in the form of motion vector plots. The procedure ascertains if specific emotions can be defined as a set of facial movements which are common to most people when they experience a particular emotion. 'Emotion vector maps' would then be established for specific emotions. These vector sets could then be applied to automated facial image analysis for security/forensic purposes. Individuals were videotaped while watching emotion-inducing short films. After the viewing of each short film, volunteers completed a brief self-reporting questionnaire to establish the emotions they experienced. The image sequences were then analysed according to emotion, by using optical flow analysis. Results were statistically analysed. Trends and analyses are presented in relation to security and video surveillance. Issues and the development of pattern recognition systems applied to human facial images for security purposes are briefly discussed

Physiological influences on continuous finger and simultaneous intra-arterial blood pressure

Because of the clinical and experimental utility of continuous finger blood pressure measurements and the need for accuracy, we tested the performance of a new hydraulic device in 22 consecutive hypertensive subjects during physiological and pharmacological interventions. Ipsilateral brachial intra-arterial pressure was monitored during rest, Valsalva's maneuver, static handgrip, and mental arithmetic and after sublingual glyceryl trinitrate. In excess of 40 000 blood pressure values were analyzed. Average bias (intra-arterial minus finger blood pressure) was 8.2±17.0 mm Hg (mean±SD, P=NS) for systolic and 2.8±10.4 mm Hg (P=NS) for diastolic pressure. Two-way ANOVA of biases with subject and task factors showed a subject effect (P<.001). Intersubject and intrasubject standard deviations of bias were 13.8 and 9.8 mm Hg systolic and 8.7 and 5.7 diastolic, respectively. Linear drift (millimeters of mercury per minute) of finger pressure was greater (P<.001) for systolic than diastolic pressure during static exercise and math and after glyceryl trinitrate. Coefficients of determination for blood pressure ranged from 0.4±0.3 to 0.8±0.3 during the tasks. We conclude that (1) noninvasive finger blood pressure faithfully follows intra-arterial changes but with clinically relevant offsets, (2) this technique is best suited for assessing pressure changes, (3) physiological and pharmacological interventions do not consistently affect finger pressure accuracy, (4) many reports of finger blood pressure measuring devices are based on direct readings obtained with inadequate system response characteristics, and (5) the tested instrument falls short of the standards requirements (bias ≤5±8 mm Hg) for devices that measure intermittently