materials and methods. In Sect. 4, we compared the clas-
sification results of four different combinations in epileptic
EEG data and five mental tasks, respectively. And Sect. 5
concluded the paper.
2 Related wor k
In the feature extraction for EEG signals, Burke et al. [5]
extend the usual autoregressive (AR) models for EEG
feature extraction. The extensi on model is an AR with
exogenous input (ARX) model for combined filtering and
feature extraction. Polat and Gu
¨
nes [6] use fast Fourier
transform as feature extraction method. Wavelet transform
is also widely used in extracting EEG features [7, 8], in
which EEG signals are decomposed by wavelet transform
to calculate approximation and detail coefficients. ApEn is
a statistical parameter that measures the predictability of
the current amplitude values of a physiological signal
based on its previous amplitude values. ApEn is used for
the first time in the proposed system for the detection of
epilepsy using neural networks [2]. A novel feature
extraction method based on multi-wavelet transform and
ApEn is proposed by Guo et al. [9]. The proposed method
uses approximate entropy features derived from multi-
wavelet transform and combines with an artificial neural
network to classify the EEG signals. Song et al. [10, 11]
use sample entropy (SampEn) as a feature extraction
method for detecting epileptic seizures. In Ref. [10],
SampEn is selected as a feature extraction method to
classify the task of three different kinds of EEG signals and
detecting epileptic seizures. Based on Ref. [10], the authors
propose an optimized sample entropy algorithm to identify
the EEG signals in [11].
Artificial neural networks (ANNs) have been widely
applied to classify EEG signals [2, 9]. Kumar et al. [7] use
discrete wavelet transform (DWT)-based ApEn and ANN to
detect epileptic seizures. SVM is also one of the classification
methods for EEG signals [3, 4]. Zhang et al. [12] present an
improved method to calculate phase locking value (PIV)
based on Hilbert–Huang transform, and the PLVs are used as
features for a least squares support vector machine (LS-SVM)
to recognize normal and hypoxia EEG. Bajaj et al. [13]
present a new method for classification of EEG signals using
empirical mode decomposition (EMD) method. The pro-
posed method for classification of EEG signals is based on the
bandwidth features and employs LS-SVM for classifying
seizure and non-seizure EEG signals. Wu et al. [14] propose a
multiscale cross-approximate entropy method to quantify the
complex fluctuation between R–R intervals series and pulse
transit time series. Ahangi et al. [15] use a multiple classifier
system for classification of EEG signals. The proposed
method uses DWT decomposition, and a variety of classifier
combination methods along with genetic algorithm feature
selection is evaluated.
3 Materials and methods
In this section, we give a description of proposed method
for EEG signal classification problem, present feature
extraction based on the WPD, and give a briefly review of
two classifiers, ELM and SVM.
Figure 1 shows the block diagram of the propos ed
method based on WPD. In our method, we first use the
WPD to decompose EEG data into sub-band signals. Then,
ApEn values or SampEn values are calculated by approx-
imation and detail coefficients. Obtained feature vectors
are used as the inputs of classifiers, such as SVM and ELM.
Last, we evaluate the classification accuracy.
3.1 Feature extraction based on wavelet packet
decomposition
Feature extraction of EEG signals includes two phases. In
the first phase, EEG signals are decomposed by the WPD to
calculate approximation and detail coefficients. In the
second phase, approximate entropy values or sample
entropy values of the approximation and detail coefficients
are calculated, which form feature vectors. These feature
vectors are used as the inputs of a classifier.
In this subsection, we first simply analyze the charac-
teristic of the WPD, and then, give a briefly review of
approximate entropy and sample entropy.
3.1.1 Wavelet packet decomposition
Feature extraction is very important to EEG signals ana-
lysis and processing. WPD is a wavelet transform where
Initial EEG data
Pre-processing
Feature extraction
WPD+ApEn/SampEn
Training data
Constructing
ELM/SVM classifier
Testing and Evaluation
Fig. 1 Block diagram of the
proposed method
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