Measuring auditory event-related potentials at the external ear canal: A demonstrative study using a new electrode and error-feedback paradigm.

Although ear canal electroencephalogram (EEG) recording has received interest from basic and applied research communities, evidence on how it can be implemented in practice is limited. The present study involving eight male participants including the authors presents the utility of our ear canal electrode and method by demonstrating both comparability of ear canal EEG to those at nearby sites and distinctiveness that ear canal event-related potentials (ERPs) could have. For this purpose, we used the balanced noncephalic electrode reference and an experimental paradigm with an error-feedback sound. Clear auditory ERPs were detected at the ear canal sites with a sufficiently low noise level comparable with those at conventional sites. The N1c, a temporal maximum subcomponent, spread over the bilateral temporal sites, including the ear canals and earlobes. While consecutive signals are generally highly similar between the ear canal and the earlobe, the N1c was larger at the ear canal than the earlobe, as demonstrated by the conventional frequentist and the hierarchical Bayesian modelling approaches. Although an evident caveat is that our sample was limited in terms of size and sex, the general capability indicates that the structure of our ear canal electrode provides EEG measurement that can be used in basic and applied settings. Our experimental method can also be an ERP-based test that conveniently assesses the capability of existing and future ear canal electrodes. The distinctive nature of the ERPs to the error-feedback sound may be utilized to examine the basic aspects of auditory ERPs and to test the processes involved in feedback-guided behaviour of participants.