168 IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION SYSTEMS, VOL. 15, NO. 1, FEBRUARY 2014
Automated Detection of Driver Fatigue Based
on Entropy and Complexity Measures
Chi Zhang, Hong Wang, and Rongrong Fu
Abstract—This paper presents a real-time method based on
various entropy and complexity measures for detection and iden-
tification of driving fatigue from recorded electroencephalogram
(EEG), electromyogram, and electrooculogram signals. The com-
plexity features were used to distinguish whether the subjects are
experienced drivers by calculating the Lempel–Ziv complexity of
EEG approximate entropy (ApEn). Different threshold values can
be set for the two kinds of drivers individually. The entropy-based
features, namely, the wavelet entropy (WE), the peak-to-peak
value of ApEn (PP-ApEn), and the peak-to-peak value of sample
entropy (PP-SampEn), were extracted from the collected signals
to estimate the driving fatigue stages. We proposed WE in a
sliding window (WES), PP-ApEn in a sliding window (PP-ApEnS),
and PP-SampEn in a sliding window (PP-SampEnS) for real-time
analysis of driver fatigue. The real-time features obtained by WE,
PP-ApEn, and PP-SampEn with sliding window were applied to
artificial neural network for training and testing the system, which
gives four situations for the fatigue level of the subjects, namely,
normal state, mild fatigue, mood swing, and excessive fatigue.
Then, the driver fatigue level can be determined in real time. The
accuracy of estimation is about 96.5%–99.5%. Receiver operating
characteristic (ROC) curve was used to present the performance
of the neural network classifier. The area under the ROC curve
is 0.9931. The results show that the developed method is valuable
for the application of avoiding some traffic accidents caused by
driver’s fatigue.
Index Terms—Driver fatigue, electroencephalogram (EEG),
electromyogram (EMG), electrooculogram (EOG), entropy, neu-
ral network.
I. INTRODUCTION
F
ATIGUE is a feeling of extreme physical or mental tired-
ness. Almost everyone becomes fatigued at some time, but
driver’s fatigue is a serious problem that leads to thousands of
automobile crashes each year [1]–[3].
Fatigue process is often a change from the alertness and
vigor state to the tiredness and weakness state. It is not only
accompanied by drowsiness but also has a negative impact
on mood. There have been studies to detect and quantify
fatigue from the measurement of physiology variables such
as electroencephalogram (EEG), electrooculogram (EOG), and
electromyogram (EMG) [4]–[6]. However, simultaneous usage
Manuscript received December 31, 2012; revised April 8, 2013 and June 23,
2013; accepted July 18, 2013. Date of publication September 5, 2013; date
of current version January 31, 2014. This work was supported in part by the
National Science Foundation of China under Grant 61071057 and in part by
the Innovation Groups of the Chinese Ministry of Education. The Associate
Editor for this paper was R. I. Hammoud. (Corresponding author: H. Wang.)
The authors are with the Department of Mechanical Engineering and
Automation, Northeastern University, Shenyang 110819, China (e-mail: zhch_
angi@163.com; hongwang@mail.neu.edu.cn; fu@ece.neu.edu).
Digital Object Identifier 10.1109/TITS.2013.2275192
and real-time analysis of EEG, EMG, and EOG signals were
not given. This is the novelty that this paper brings.
The EEG signals do a pretty good job of state discrimination.
All the physical and mental activities associated with driving
are reflected in EEG signals [4]. The EMG signals are influ-
enced by muscle activities; a person gets lower tonus of EMG
when his fatigue process gets further [7]. The EOG signals can
be very useful to detect drowsiness. It has been observed that
eye movement decreases while blink rate increases as a person
enters into the state of fatigue [8]. Obviously, the simultaneous
usage of EEG, EMG, and EOG signals can increase the accu-
racy of identification and classification results.
The recorded physiological signals are nonlinear, time-
varying, space-varying, and nonstationary in nature. Nonlinear
dynamical analysis can provide complementary information
about the dynamics under physiological or psychological states
compared with classical linear time series analysis methods
such as Fourier or spectral analysis [9], [10]. Nonlinear dynam-
ical analysis techniques derived from the theory of nonlinear
dynamical systems such as the correlation integral, Lyapunov
exponents, and correlation dimension have been recently used
in a number of fields of application. Assessment of driver’s
fatigue is one of the special application areas [4], [11], [12].
One approach to the nonlinear estimation of dynamical
EEG, EOG, and EMG activity is complexity analysis. Among
complexity analysis approaches, entropy-based algorithms have
been useful and robust estimators for evaluating regularity or
predictability [13]. Shannon entropy (SE) is a disorder quan-
tifier and is a measure of the flatness of energy spectrum in
the wavelet domain [4], [14]. In this paper, we use the energy
sequence distribution to replace the distribution of the prob-
ability distribution of SE to calculate wavelet entropy (WE).
Approximate entropy (ApEn) and its refined version, i.e., sam-
ple entropy (SampEn), were developed as practically tractable
physiological measures in view of their robustness to noise and
finitude of data sets and applicability to stochastic, nonlinear
deterministic, and composite processes [15], [16]. Lempel–Ziv
complexity (LZC) is an approach to the problem that links the
complexity of a specific sequence to the gradual buildup of new
patterns along the given sequence [17]. It can show the approx-
imation degree between finite sequence and random sequence.
The greater the LZC of the sequence is, the closer to random
sequence it will be. EEG LZC, which reflects the amount of the
EEG information, can reveal brain activity regularity [18].
This paper presents a methodology for automatic detection
of normal and fatigue states from recorded EEG, EOG, and
EMG signals. The complexity features were used to distinguish
whether the subjects are experienced drivers by calculating the
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