An official website of the United States government
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.
more »
« less
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.
more »
« less
- Award ID(s):
- 1829310
- 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
More Like this
-
-
Abstract Background Tympanometry is used as part of a battery of tests for screening of middle ear function and may help diagnose middle ear disorders, but remains available only on expensive test equipment. Methods We report a low-cost smartphone-based tympanometer system that consists of a lightweight and portable attachment to vary air pressure in the ear and measure middle ear function. The smartphone displays a tympanogram and reports peak acoustic admittance in realtime. Our programmable and open-source system operates at 226 Hz and was tested on 50 pediatric patient ears in an audiology clinic in parallel with a commercial tympanometer. Results Our study shows an average agreement of 86 ± 2% between the 100 tympanograms produced by the smartphone and commercial device when five pediatric audiologists classified them into five classes based on the Liden and Jerger classification. Conclusion Given the accessibility and prevalence of budget smartphones in developing countries, our open-source tool may help provide timely and affordable screening of middle ear disorders.more » « less
-
Otitis media (OM) is the most common disease among young children and one of the most frequent reasons to visit the pediatrician. Development of OM requires nasopharyngeal colonization by a pathogen which must gain access to the tympanic cavity through the eustachian tube (ET) along with being able to overcome the defense mechanisms of the immune system and middle ear mucosa. OM can be caused by viral or bacterial infection. The three main bacterial pathogens are Streptococcus pneumoniae, nontypeable Haemophilus influenzae (NTHi), and Moraxella catarrhalis. Innate immunity is important in OM resolution as the disease occurs in very young children before the development of specific immunity. Elements of innate immunity include natural barriers and pattern recognition receptors such as Toll like receptors (TLRs), and Nod like receptors (NLRs). Surfactant proteins A (SP-A) and D (SP-D) act as pattern recognition receptors and are found in the lung and many other tissues including the ET and the middle ear where they probably function in host defense. Surfactant has a potential for use in the treatment of OM due to surface tension lowering function in the ET, and the possible immune functions of SP-D and SP-A in the middle ear and ET.more » « less
-
ABSTRACT The study of primate auditory morphology is a significant area of interest for comparative anatomists, given the phylogenetic relationships that link primate hearing and the morphology of these auditory structures. Extensive literature addresses the form‐to‐function relationship of the auditory system (outer, middle, and inner ear) in primates and, by extension, provides insight into the auditory system of extinct primates and even modern humans. We add to this literature by describing the ontogenetic trajectory of the middle ear cavity and ossicular chain (malleus, incus, and stapes) due to their critical role in relaying auditory stimuli for interpretation. We examined middle ear morphology in neonatal primates and adult primates using a taxonomically broad sample. We focused primarily on nocturnal primate taxa (Daubentonia,Loris,Galago,Aotus, andTarsier), which are underrepresented in the literature. However, we also included three diurnal taxa (Macaca,Lemur, andSaguinus). Using 3D Slicer, we visualized middle ear structures in three dimensions using conventional micro CT data informed by diffusible iodine‐based contrast‐enhanced CT (diceCT) data. We illustrated how spatial relationships between otic elements, such as the various epitympanic sinuses of the middle ear and the auditory ossicles, vary throughout ontogeny. Our major findings include that the central tympanic cavity scaled with negative allometry in all taxa and that the accessory cavities scaled with isometry or positive allometry in most taxa. Despite these changes in chamber size, the size of the ear ossicles remained relatively consistent through ontogeny in most taxa. We confirmed our expectation that anthropoids exhibit an increase in the complexity of accessory cavities throughout ontogeny, mirroring the exponential pneumatization of the face in anthropoids. These findings provide an ontogenetic perspective and reveal further functional complexities of the middle ear as a conduit for sound proliferation and as a pressure regulator.more » « less
-
Abstract The study of the impedance mismatch between the device and its surroundings is crucial when building an acoustic device to obtain optimal performance. In reality, a high impedance mismatch would prohibit energy from being transmitted over the interface, limiting the amount of energy that the device could treat. In general, this is solved by using acoustic impedance matching layers, such as gradients, similar to what is done in optical coatings. The simplest form of such a gradient can be considered as an intermediate layer with certain qualities resting between the two media to impedance match, and requiring a minimum thickness of at least one quarter wavelength of the lowest frequency under consideration. The desired combination(s) of the (limited) available elastic characteristics and densities has traditionally determined material selection. Nature, which is likewise limited by the use of a limited number of materials in the construction of biological structures, demonstrates a distinct approach in which the design space is swept by modifying certain geometrical and/or material parameters. The middle ear of mammals and the lateral line of fishes are both instances of this method, with the latter already incorporating an architecture of distributed impedance matched underwater layers. In this paper, we develop a resonant mechanism whose properties can be modified to give impedance matching at different frequencies by adjusting a small set of geometrical parameters. The mechanism in question, like the lateral line organ, is intended to serve as the foundation for the creation of an impedance matching meta-surface. A computational study and parameter optimization show that it can match the impedance of water and air in a deeply sub-wavelength zone.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fbioe.2022.983510
