Custom-Fitted In- and Around-the-Ear Sensors for Unobtrusive and On-the-Go EEG Acquisitions: Development and Validation.

Olivier Valentin,Hami Monsarat-Chanon,Jérémie Voix,Aidin Delnavaz,Mikaël Ducharme,Guilhem Viallet,Gabrielle Cretot-Richert

doi:10.3390/s21092953

Abstract

Objectives: This paper aims to validate the performance and physical design of a wearable, unobtrusive ear-centered electroencephalography (EEG) device, dubbed “EARtrodes”, using early and late auditory evoked responses. Results would also offer a proof-of-concept for the device to be used as a concealed brain–computer interface (BCI). Design: The device is composed of a custom-fitted earpiece and an ergonomic behind-the-ear piece with embedded electrodes made of a soft and flexible combination of silicone rubber and carbon fibers. The location of the conductive silicone electrodes inside the ear canal and the optimal geometry of the behind-the-ear piece were obtained through morphological and geometrical analysis of the human ear canal and the region around-the-ear. An entirely conductive generic earpiece was also developed to assess the potential of a universal, more affordable solution. Results: Early latency results illustrate the conductive silicone electrodes’ capability to record quality EEG signals, comparable to those obtained with traditional gold-plated electrodes. Additionally, late latency results demonstrate EARtrodes’ capacity to reliably detect decision-making processes from the ear. Conclusions: EEG results validate the performance of EARtrodes as a circum-aural and intra-aural EEG recording system adapted for a wide range of applications in audiology, neuroscience, clinical research, and as an unobtrusive BCI.

Highlights

Electroencephalography (EEG) is a valuable tool for understanding brain function.It has been widely used for medical diagnoses, neurocognitive research and brain–computer interfaces (BCI) [1]
This observation is supported by a two-sample t-test for noninferiority [38] computed using R 3.6.1 with MASS 7.3–51.4 [39], which rejects the null hypothesis at a 5% significance level (p = 1.84 × 10−6 with a margin tolerance ε = ±σ) and confirms the idea that the comfort of the custom in-ear device is noninferior to the comfort of the generic in-ear device, whereas a two-sample t-test for nonsuperiority fails to reject the null hypothesis at a 5% significance level (p = 0.1113 with the same margin tolerance ε = ±σ), supporting the idea that the comfort of the custom in-ear device is superior to the comfort of the generic in-ear device
A Friedman rank sum test [40] procedure confirms that gold-plated electrodes and conductive silicone electrodes are not equivalent with respect to impedances as this test rejects the null hypothesis at a 5% significance level (p = 3.773 × 10−12 )

Summary

Introduction

Electroencephalography (EEG) is a valuable tool for understanding brain function. It has been widely used for medical diagnoses, neurocognitive research and brain–computer interfaces (BCI) [1]. Conventional EEG systems measure the brain’s electrical activity using caps, which maintain electrodes in contact with the skull (scalp-EEG) and which are connected to wires transmitting the signals to differential amplifiers connected to a computer. EEG caps are uncomfortable to wear, impractical for daily-life situations and inadequate for social settings. These restrictions limit the research questions that can be addressed with conventional EEG and prevent its extensive potential for BCI applications [2]

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