Pengaruh Ciri Temporal, Spasial, dan Frekuensi pada Klasifikasi Motor Imagery

Interaksi mesin-komputer merupakan suatu keniscayaan dan akan menjadi bagian yang tidak terpisahkan dari kehidupan dalam waktu dekat, terutama di bidang rekayasa rehabilitasi. Salah satu bidang yang berkembang adalah klasifikasi Motor Imagery (MI) berbasis sinyal EEG. Set data pada studi ini diambil dari BCI Competition IV - 2b. Prapemrosesan data dilakukan dengan menggunakan BPF Butterworth orde 5 dengan frekuensi cut-off sebesar 8 – 30 Hz.  Pada studi ini, dilakukan investigasi pengaruh ciri temporal; spasial; dan frekuensi serta kombinasi ciri temporal-spasial dan temporal-spasial-frekuensi. Ciri temporal diekstraksi dengan menggunakan ICA, ciri spasial dengan CSP, dan frekuensi dengan STFT. Terdapat empat pengklasifikasi yang digunakan, yaitu SVM; RF; k-NN; dan NB. Salah satu temuan pada studi ini adalah meskipun digunakan kombinasi ciri temporal-spasial maupun temporal-spasial-frekuensi, nilai akurasi yang diperoleh sama, yaitu sekitar 72%. Kinerja kedua kombinasi ciri ini masih kalah apabila dibandingkan dengan hanya menggunakan ciri independen temporal dengan nilai akurasi mencapai 73%. Selain itu, pengklasifikasi RF memberikan kinerja yang paling baik dibandingkan dengan SVM; k-NN; serta NB.  Abstract Human-computer interaction is a necessity and will be deployed in the near future, especially in rehabilitation engineering. One of the development is focused on the classification of Imagery Motor (MI) based on EEG signals. In this study, the dataset is taken from BCI Competition IV - 2b. The first step of the classification process is data preprocessing that is performed using BPF Butterworth 5th order with a cut-off frequency of 8 - 30 Hz. The aim of this study is to investigate the effect of independent feature such as temporal, spatial, frequency, and the combination of temporal-spatial and temporal-spatial-frequency features. Temporal feature is extracted using ICA, spatial feature using CSP, and frequency feature using STFT. In this study, four classifiers are used, i.e., SVM; RF; k-NN; and NB. One of the main findings in this study is that although the combination of temporal-spatial and temporal-spatial-frequency features is used, the accuracy value of 72% are obtained. The performance of these two combinations of features is still inferior when compared to independent temporal feature with an accuracy value of 73%. In addition, RF classifier provides the best performance compared to SVM; k-NN; and NB. Keywords: motor imagery, temporal, spatial, frequency, random fores

Learning Common Time-Frequency-Spatial Patterns for Motor Imagery Classification.

The common spatial patterns (CSP) algorithm is the most popular spatial filtering method applied to extract electroencephalogram (EEG) features for motor imagery (MI) based brain-computer interface (BCI) systems. The effectiveness of the CSP algorithm depends on optimal selection of the frequency band and time window from the EEG. Many algorithms have been designed to optimize frequency band selection for CSP, while few algorithms seek to optimize the time window. This study proposes a novel framework, termed common time-frequency-spatial patterns (CTFSP), to extract sparse CSP features from multi-band filtered EEG data in multiple time windows. Specifically, the whole MI period is first segmented into multiple subseries using a sliding time window approach. Then, sparse CSP features are extracted from multiple frequency bands in each time window. Finally, multiple support vector machine (SVM) classifiers with the Radial Basis Function (RBF) kernel are trained to identify the MI tasks and the voting result of these classifiers determines the final output of the BCI. This study applies the proposed CTFSP algorithm to three public EEG datasets (BCI competition III dataset IVa, BCI competition III dataset IIIa, and BCI competition IV dataset 1) to validate its effectiveness, compared against several other state-of-the-art methods. The experimental results demonstrate that the proposed algorithm is a promising candidate for improving the performance of MI-BCI systems

A Novel Classification Framework Using the Graph Representations of Electroencephalogram for Motor Imagery based Brain-Computer Interface

The motor imagery (MI) based brain-computer interfaces (BCIs) have been proposed as a potential physical rehabilitation technology. However, the low classification accuracy achievable with MI tasks is still a challenge when building effective BCI systems. We propose a novel MI classification model based on measurement of functional connectivity between brain regions and graph theory. Specifically, motifs describing local network structures in the brain are extracted from functional connectivity graphs. A graph embedding model called Ego-CNNs is then used to build a classifier, which can convert the graph from a structural representation to a fixed-dimensional vector for detecting critical structure in the graph. We validate our proposed method on four datasets, and the results show that our proposed method produces high classification accuracies in two-class classification tasks (92.8% for dataset 1, 93.4% for dataset 2, 96.5% for dataset 3, and 80.2% for dataset 4) and multiclass classification tasks (90.33% for dataset 1). Our proposed method achieves a mean Kappa value of 0.88 across nine participants, which is superior to other methods we compared it to. These results indicate that there is a local structural difference in functional connectivity graphs extracted under different motor imagery tasks. Our proposed method has great potential for motor imagery classification in future studies

Internal Feature Selection Method of CSP Based on L1-Norm and Dempster–Shafer Theory

The common spatial pattern (CSP) algorithm is a well-recognized spatial filtering method for feature extraction in motor imagery (MI)-based brain–computer interfaces (BCIs). However, due to the influence of nonstationary in electroencephalography (EEG) and inherent defects of the CSP objective function, the spatial filters, and their corresponding features are not necessarily optimal in the feature space used within CSP. In this work, we design a new feature selection method to address this issue by selecting features based on an improved objective function. Especially, improvements are made in suppressing outliers and discovering features with larger interclass distances. Moreover, a fusion algorithm based on the Dempster–Shafer theory is proposed, which takes into consideration the distribution of features. With two competition data sets, we first evaluate the performance of the improved objective functions in terms of classification accuracy, feature distribution, and embeddability. Then, a comparison with other feature selection methods is carried out in both accuracy and computational time. Experimental results show that the proposed methods consume less additional computational cost and result in a significant increase in the performance of MI-based BCI systems

Random subspace K-NN based ensemble classifier for driver fatigue detection utilizing selected EEG channels

Nowadays, many studies have been conducted to assess driver fatigue, as it has become one of the leading causes of traffic crashes. However, with the use of advanced features and machine learning approaches, EEG signals may be processed in an effective way, allowing fatigue to be detected promptly and efficiently. An optimal channel selection approach and a competent classification algorithm might be viewed as a critical aspect of efficient fatigue detection by the driver. In the present framework, a new channel selection algorithm based on correlation coefficients and an ensemble classifier based on random subspace k-nearest neighbour (k-NN) has been presented to enhance the classification performance of EEG data for driver fatigue detection. Moreover, power spectral density (PSD) was used to extract the feature, confirming the presented method's robustness. Additionally, to make the fatigue detection system faster, we conducted the experiment in three different time windows, including 0.5s, 0.75s, and 1s. It was found that the proposed method attained classification accuracy of 99.99% in a 0.5 second time window to identify driver fatigue by means of EEG. The outstanding performance of the presented framework can be used effectively in EEG-based driver fatigue detection

Subject-independent EEG classification based on a hybrid neural network

A brain-computer interface (BCI) based on the electroencephalograph (EEG) signal is a novel technology that provides a direct pathway between human brain and outside world. For a traditional subject-dependent BCI system, a calibration procedure is required to collect sufficient data to build a subject-specific adaptation model, which can be a huge challenge for stroke patients. In contrast, subject-independent BCI which can shorten or even eliminate the pre-calibration is more time-saving and meets the requirements of new users for quick access to the BCI. In this paper, we design a novel fusion neural network EEG classification framework that uses a specially designed generative adversarial network (GAN), called a filter bank GAN (FBGAN), to acquire high-quality EEG data for augmentation and a proposed discriminative feature network for motor imagery (MI) task recognition. Specifically, multiple sub-bands of MI EEG are first filtered using a filter bank approach, then sparse common spatial pattern (CSP) features are extracted from multiple bands of filtered EEG data, which constrains the GAN to maintain more spatial features of the EEG signal, and finally we design a convolutional recurrent network classification method with discriminative features (CRNN-DF) to recognize MI tasks based on the idea of feature enhancement. The hybrid neural network proposed in this study achieves an average classification accuracy of 72.74 ± 10.44% (mean ± std) in four-class tasks of BCI IV-2a, which is 4.77% higher than the state-of-the-art subject-independent classification method. A promising approach is provided to facilitate the practical application of BCI