Subject Specific Deep Learning Model for Motor Imagery Direction Decoding

TL;DR

This paper introduces a novel deep learning framework using EEGNet with SE layers for online decoding of unilateral motor imagery directions, improving accuracy and providing electrode importance insights for BCI applications.

Contribution

It presents a subject-independent deep learning model with SE layers for online unilateral MI decoding, enhancing accuracy and interpretability over existing models.

Findings

Achieved 58.7% average binary decoding accuracy

Outperformed existing deep learning models in MI direction decoding

SE layers provided insights into electrode importance

Abstract

Hemispheric strokes impair motor control in contralateral body parts, necessitating effective rehabilitation strategies. Motor Imagery-based Brain-Computer Interfaces (MI-BCIs) promote neuroplasticity, aiding the recovery of motor functions. While deep learning has shown promise in decoding MI actions for stroke rehabilitation, existing studies largely focus on bilateral MI actions and are limited to offline evaluations. Decoding directional information from unilateral MI, however, offers a more natural control interface with greater degrees of freedom but remains challenging due to spatially overlapping neural activity. This work proposes a novel deep learning framework for online decoding of binary directional MI signals from the dominant hand of 20 healthy subjects. The proposed method employs EEGNet-based convolutional filters to extract temporal and spatial features. The EEGNet model is enhanced by Squeeze-and-Excitation (SE) layers that rank the electrode importance and feature maps. A subject-independent model is initially trained using calibration data from multiple subjects and fine-tuned for subject-specific adaptation. The performance of the proposed method is evaluated using subject-specific online session data. The proposed method achieved an average right vs left binary direction decoding accuracy of 58.7 +\- 8% for unilateral MI tasks, outperforming the existing deep learning models. Additionally, the SE-layer ranking offers insights into electrode contribution, enabling potential subject-specific BCI optimization. The findings highlight the efficacy of the proposed method in advancing MI-BCI applications for a more natural and effective control of BCI systems.