Decoding auditory-evoked response in affective states using wearable around-ear EEG system

Objective. In this paper, an around-ear EEG system is investigated as an alternative methodology to conventional scalp-EEG-based systems in classifying human affective states in the arousal-valence domain evoked in response to auditory stimuli. Approach. EEG recorded from around the ears is compared to EEG collected according to the international 10-20 system in terms of efficacy in an affective state classification task. A wearable device with eight dry EEG channels is designed for ear-EEG acquisition in this study. Twenty-one subjects participated in an experiment consisting of six sessions over three days using both ear and scalp-EEG acquisition methods. Experimental tasks consisted of listening to an auditory stimulus and self-reporting the elicited emotion in response to the said stimulus. Various features were used in tandem with asymmetry methods to evaluate binary classification performances of arousal and valence states using ear-EEG signals in comparison to scalp-EEG. Main results. Weachieve an average accuracy of 67.09% +/- 6.14 for arousal and 66.61% +/- 6.14 for valence after training a multi-layer extreme learning machine with ear-EEG signals in a subject-dependent context in comparison to scalp-EEG approach which achieves an average accuracy of 68.59% +/- 6.26 for arousal and 67.10% +/- 4.99 for valence. In a subject-independent context, the ear-EEG approach achieves 63.74% +/- 3.84 for arousal and 64.32% +/- 6.38 for valence while the scalp-EEG approach achieves 64.67% +/- 6.91 for arousal and 64.86% +/- 5.95 for valence. The best results show no significant differences between ear-EEG and scalp-EEG signals for classifications of affective states. Significance. To the best of our knowledge, this paper is the first work to explore the use of around-ear EEG signals in emotion monitoring. Our results demonstrate the potential use of around-ear EEG systems for the development of emotional monitoring setups that are more suitable for use in daily affective life log systems compared to conventional scalp-EEG setups.