Adaptive Segmentation Approach for an Improved Classification of MI-EEG Signals

Öz

Electroencephalogram (EEG)-based brain-computer interfaces (BCI) rely on effective design of signal processing pipelines to achieve high classification performance. The fundamental EEG signal processing steps include preprocessing, feature extraction, selection, and classification. In the feature extraction step, EEG signals are typically segmented using a fixed window length. This study proposes an adaptive segmentation scheme using change point detection (CPD) to achieve optimal segmentation for enhanced feature representation. Pruned exact linear time (PELT) algorithm was used to detect change points by minimizing a cost function with a sensitivity parameter for avoiding over segmentation. The proposed and fixed-point segmentation approaches were evaluated using BCI Competition IV dataset 2a, which contains EEG recordings from 9 subjects performing motor imagery tasks involving left-hand, righthand, foot and tongue movements. Results demonstrated that the CPD-based method improved classification performance on test data for both binary and four-class classification tasks. In binary classification, performance improvement ranged from 5.81% to 8.72%, depending on class pair. The highest classification performance was observed in left hand and tongue movements, with participantspecific improvements ranging from 4.16% to 12.73%. In four-class task, an average improvement of 7.5% was observed, with participant-specific improvements ranging from 3.93% to 11.11%.

Anahtar Kelimeler

• EEG
• Motor Imagery
• Change Point Detection
• Fixed Point Segmentation
• Classification

MOTOR İMGELEME EEG SİNYALLERİNDE SINIFLANDIRMA PERFORMANSINI ARTTIRMAYA YÖNELİK ADAPTİF SEGMENTASYON YAKLAŞIMI

Öz

Elektroansefalogram (EEG) tabanlı beyin-bilgisayar arayüzlerinin (BBA) performansı, sistem tasarımında kullanılan sinyal işleme yöntemlerine doğrudan bağlıdır. EEG sinyal işleme süreci; önişleme, öznitelik çıkarma, seçme ve sınıflandırma adımlarını içerir. EEG verilerinden öznitelik çıkarımı genellikle sabit uzunlukta pencerelere ayrıldıktan sonra yapılmaktadır. Bu çalışmada özniteliklerin veri temsiliyetini artırmak için değişim noktası tespitine (change point detection, CPD) dayalı adaptif bir segmentasyon yaklaşımı önerilmiştir. Bu amaçla budanmış kesin doğrusal zaman (pruned exact linear time, PELT) algoritması kullanılmıştır. Bu yöntem, değişim noktalarını uygun bir maliyet fonksiyonu ile duyarlılık parametresinin belirlenmesi yoluyla tespit etmektedir. Önerilen yöntemin, sabit segmentasyona kıyasla etkinliği, BCI Competition IV 2a veri seti kullanılarak değerlendirilmiştir. Bu veri seti, 9 katılımcının sol el, sağ el, ayak ve dil imgeleme görevlerini gerçekleştirirken kaydedilmiş EEG verilerini içermektedir. Sonuçlar, CPD tabanlı yöntemin hem ikili hem de dört sınıflı sınıflandırmada test verisi üzerindeki sınıflandırma başarımını artırdığını göstermiştir. İkili sınıflandırma senaryosunda, önerilen yöntemin performans artışı %5,81 ile %8,72 arasında değişmiştir. En yüksek sınıflandırma performansı, sol el ve dil görevleri arasında gözlemlenmiş; katılımcı bazında performans artışları %4,16 ve %12,73 aralığında değişmiştir. Dört sınıflı sınıflandırma görevinde ise ortalama %7,5 oranında bir başarı artışı sağlanmış olup, katılımcı bazlı performans artışları %3,93 ile %11,11 aralığında değişmiştir.

Anahtar Kelimeler

• EEG
• Motor İmgeleme
• Değişim Noktası Tespiti
• Sabit Süreli Segmentasyon
• Sınıflandırma

Kaynakça

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