The Effects of Middle-ear Stiffness on the Auditory Brainstem Neural Encoding of Phase

• Published in: Journal of the Association for Research in Otolaryngology Vol. 23; no. 6; pp. 859 - 873
• Main Authors: Racca, Jordan M., Delgado, Rafael E., Gifford, René H., Ramachandran, Ramnarayan, Hood, Linda J.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.12.2022; Springer Nature B.V
• Subjects: Absorbance; Acoustic Stimulation; Acoustics; Adult; Auditory Threshold - physiology; Brain Stem; Cochlea; Cochlear Nerve; Ear; Ear, Middle - physiology; Ears & hearing; Hearing; Hearing Tests - methods; Humans; Localization; Medicine; Medicine & Public Health; Neural coding; Neurobiology; Neurosciences; Otorhinolaryngology; Research Article; Statistical analysis; phase; auditory steady-state response; auditory brainstem; middle-ear stiffness
• ISSN: 1438-7573; 1525-3961; 1438-7573
• DOI: 10.1007/s10162-022-00872-0

The middle-ear system relies on a balance of mass and stiffness characteristics for transmitting sound from the external environment to the cochlea and auditory neural pathway. Phase is one aspect of sound that, when transmitted and encoded by both ears, contributes to binaural cue sensitivity and spatial hearing. The study aims were (i) to investigate the effects of middle-ear stiffness on the auditory brainstem neural encoding of phase in human adults with normal pure-tone thresholds and (ii) to investigate the relationships between middle-ear stiffness-induced changes in wideband acoustic immittance and neural encoding of phase. The auditory brainstem neural encoding of phase was measured using the auditory steady-state response (ASSR) with and without middle-ear stiffness elicited via contralateral activation of the middle-ear muscle reflex (MEMR). Middle-ear stiffness was quantified using a wideband acoustic immittance assay of acoustic absorbance. Statistical analyses demonstrated decreased ASSR phase lag and decreased acoustic absorbance with contralateral activation of the MEMR, consistent with increased middle-ear stiffness changing the auditory brainstem neural encoding of phase. There were no statistically significant correlations between stiffness-induced changes in wideband acoustic absorbance and ASSR phase. The findings of this study may have important implications for understanding binaural cue sensitivity and horizontal plane sound localization in audiologic and otologic clinical populations that demonstrate changes in middle-ear stiffness, including cochlear implant recipients who use combined electric and binaural acoustic hearing and otosclerosis patients.