Properties of the coherence function between a sound envelope and magnetoencephalogram data in a selective listening study

Abstract

As a novel method for analyzing the auditory-evoked brain response, we used the coherence function between a sound envelope and brain signal, such as a signal acquired on a magnetoencephalogram (MEG) or an electroencephalogram (EEG), in a selective listening study. In this study, we examined mixed sounds with various mixing ratios and investigated how the coherence value changes according to the ease of hearing. We used two types of mixed sounds: speech mix and music mix. We investigated three types of mixing ratios: easy, normal, and difficult with respect to hearing the target sound. MEG recording was obtained as each mixed sound was heard. We calculated the coherence function between the sound envelope and the MEG data. This is a function of the frequency, and a higher coherence value indicates that both signals have higher correlation at that frequency. We found that the coherence value tends to increase according to the easiness of hearing the target sound. This property might be useful for developing a new-type of hearing aid for selective listening.