Discrimination of Wakefulness From Sleep Stage I Using Nonlinear Features of a Single Frontal EEG Channel

Abstract

Objective: Although a wide range of researches have shown the utility of electroencephalography (EEG) for the sleep monitoring, the majority of them reported a low sensitivity for classification of wakefulness from sleep stage I. This paper, therefore, validates a reliable nonlinear feature set for discriminating the wakefulness from sleep stage I using a single frontal EEG channel. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Methods</i> : Effectiveness of the proposed feature set was evaluated using four public databases namely Sleep Telemetry, DREAMS, MESA, and DCSM. After splitting the EEG signal into its sub-bands using discrete wavelet transform, Katz and Higuchi’s fractal dimensions, dispersion entropy, and bubble entropy were computed as the features. Then, 70% of the samples was randomly fed to the support vector machine, linear discriminant analysis, and k-nearest neighbors classifiers with 10-fold cross-validation for the training, whereas the rest was used for the unseen data testing. We also compared performance of the proposed feature set against the relative band power (RBP) analysis. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Results</i> : While the best classification results for both feature sets were achieved by the support vector machine, the proposed outperformed the RBP with the higher mean of sensitivity to sleep stage I for the Sleep Telemetry (82.6% vs. 71.8%, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p} &lt; 0.05$ </tex-math></inline-formula> ), DREAMS (87.6% vs. 71.8%, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p} &lt; 0.05$ </tex-math></inline-formula> ), DCSM (91.0% vs. 74.2%, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p} &lt; 0.05$ </tex-math></inline-formula> ), and MESA (82.0% vs. 76.1%, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p} &lt; 0.05$ </tex-math></inline-formula> ) databases. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Significance</i> : Considering interchangeability of the proposed feature set for discriminating the wakefulness from sleep stage I, it has the potential to be used for estimating the sleep onset latency in clinical applications.