Systematic Investigation of Optimal Electrode Positions and Re-referencing Strategies on Ear Biosignals

This study aims to determine the optimal electrode positions and re-referencing strategies for ear biosignals by systematically comparing ear and conventional biosignals. We analyzed four physiological signals: electroencephalography (EEG), electromyography (EMG), electrooculography (EOG), and electrocardiography (ECG), with five re-referencing strategies. The signals were recorded from conventional locations and around the ears. Quantitative measures, such as the signal-to-noise ratio, recall, and correlation, were employed to identify the optimal electrode positions and re-referencing strategies for each physiological signal type. The optimal ear electrode positions were selected based on their proximity to conventional configurations: the upper part/behind the ear for EEG, the lower part for blink detection and vertical EOG, and the front for clench EMG and horizontal EOG. While no single re-referencing strategy consistently performed best for all physiological signals, we found that (mean-)ipsilateral re-referencing strategies were more suitable for EEG, EMG, blink detection, and vertical EOG, whereas (mean-)contralateral re-referencing strategies were more effective for horizontal EOG and ECG compared to other strategies. The optimal ear electrode positions and re-referencing methods varied slightly across subjects and demonstrated comparable performance to the conventional configurations in terms of quantitative measures. Ear biosignals have the potential for use in developing human-computer interfaces with comparable performance to conventional electrode configuration while being more practical in terms of attachment and detachment. This study provides in-depth insight into the optimal electrode locations and re-referencing strategy for developing ear-biosignal-based human-computer-interface applications.本研究旨在通过系统对比耳部与传统生物信号，确定耳部生物信号的最优电极位置与参考重设策略。我们分析了四类生理信号：脑电图（electroencephalography，EEG）、肌电图（electromyography，EMG）、眼电图（electrooculography，EOG）以及心电图（electrocardiography，ECG），并设置了五种参考重设策略（re-referencing strategies）。上述信号分别采集于传统电极位置与耳部周边区域。本研究采用信噪比、召回率与相关性等量化指标，以确定适配每一类生理信号的最优电极位置与参考重设策略。基于与传统电极配置的接近程度，优选的耳部电极位置为：脑电图对应耳部上方/耳后区域，眨眼检测与垂直眼电图对应耳下部区域，而握拳肌电图与水平眼电图对应耳前部区域。尽管没有单一的参考重设策略能在所有生理信号中始终表现最优，但我们发现（均值）同侧参考重设策略更适配脑电图、肌电图、眨眼检测与垂直眼电图；而相较于其他策略，（均值）对侧参考重设策略在水平眼电图与心电图中效果更优。最优耳部电极位置与参考重设方法存在轻微的个体差异，且其量化指标表现与传统电极配置相当。耳部生物信号有望用于开发性能可媲美传统电极配置的人机交互界面，且在佩戴与拆卸方面更具实用性。本研究为开发基于耳部生物信号的人机交互界面应用，提供了关于最优电极位置与参考重设策略的深度见解。