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. Here, we present a quantitative analysis of electrode-skin impedance for dry-contact in-ear EEG that accounts for cerumen (earwax) and electrodermal (sweat gland) response. Custom fitted earmolds with 16 embedded electrodes were developed to map the skin conductance in the ear canal of 3 subjects. In the presence of cerumen, the measured average dry-contact impedance in the ear canal was 86% higher than canals removed of cerumen. Electrodermal activity was also found to play a role in electrode-skin impedance, showing up to 25% decrease in dry-contact impedance in response to tactile stimulation. The better understanding of the dynamics of in-ear conditions serves to improve consistency and accuracy of in-ear electrophysiology.
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Mammalian middle ear mechanics: A review
The middle ear is part of the ear in all terrestrial vertebrates. It provides an interface between two media, air and fluid. How does it work? In mammals, the middle ear is traditionally described as increasing gain due to Helmholtz’s hydraulic analogy and the lever action of the malleus-incus complex: in effect, an impedance transformer. The conical shape of the eardrum and a frequency-dependent synovial joint function for the ossicles suggest a greater complexity of function than the traditional view. Here we review acoustico-mechanical measurements of middle ear function and the development of middle ear models based on these measurements. We observe that an impedance-matching mechanism (reducing reflection) rather than an impedance transformer (providing gain) best explains experimental findings. We conclude by considering some outstanding questions about middle ear function, recognizing that we are still learning how the middle ear works.
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- Award ID(s):
- 1829310
- NSF-PAR ID:
- 10398502
- Date Published:
- Journal Name:
- Frontiers in Bioengineering and Biotechnology
- Volume:
- 10
- ISSN:
- 2296-4185
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fbioe.2022.983510
