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In-Ear Electrophysiology for Unobtrusive Auditory Brain-Machine Interfaces


Conventional electroencephalography (EEG) requires placement of several electrode sensors on the scalp and, accompanied by lead wires and bulky instrumentation, makes for an uncomfortable experience. Recent efforts in miniaturization and system integration have enabled smaller systems, such as wearable, in-ear EEG devices that are gaining popularity for their unobtrusive form factor. Although in-ear EEG has been demonstrated in recent works, dynamics of the ear and ear canal that directly affect electrophysiological measurements have been largely ignored. Further, the density of electrodes used currently in the ear and the regions of the ear being utilized still remains limited. Development of advanced acquisition hardware and higher-density electrode recording apparatus is necessary to improve performance and usability of the ear for electrophysiological applications. Here, I present the work undertaken to develop bioinstrumentation hardware and custom-fitted in-ear devices for high-quality electrophysiological recordings from within the ear to unobtrusively evaluate brain state and auditory stimulus response. The hardware system performance is rigorously validated using standard bench top testing procedures. I present a quantitative analysis of electrode-skin impedance for dry-contact in-ear EEG that accounts for cerumen (earwax) and electrodermal (sweat gland) response. The presence of cerumen increases dry contact electrode impedance significantly and electrodermal activity was also found to play a role in electrode-skin impedance, showing a decrease in dry-contact impedance in response to tactile stimulation. Moreover, auditory stimulus response of the brain was evaluated from EEG measurements taken in-ear and compared to the commercial scalp measurements.

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