Changes in the Compressive Nonlinearity of the Cochlea During Early Aging: Estimates From Distortion OAE Input/Output Functions.
Amanda J Ortmann, Carolina Abdala
PMID 27232070WHAT IT FOUND
Middle-aged ears showed less cochlear compression than young ears.
The response grew over a wider range of sound levels before flattening. Hearing thresholds partly explained it, but age still accounted for changes at some frequencies.
Key findings
01Middle-aged adults had distortion OAE amplitudes reduced by 11.5 dB at one tested level and DPOAE thresholds of 40 dB SPL versus 26 dB SPL in young adults.
02The compression threshold was significantly higher in the middle-aged group, and the compression range was reduced.
03After high-frequency hearing thresholds were controlled, age remained an independent predictor of compression threshold at 2607 Hz and 7394 Hz, but not at 3696 Hz or 5207 Hz.
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What it does not show
The study included 30 adults total, with 15 in each age group, so it was a small laboratory comparison. The middle-aged group was not old: the mean age was 52 years, and only one subject was 64 years old, so the findings describe early aging only. The two groups differed in audiometric thresholds by 9.4 dB on average from 2 to 8 kHz, and the authors state this can confound the age effect. Some middle-aged input/output functions did not fit the standard compression model well. Assigned thresholds or alternative fits were used. The emissions provide an indirect estimate of cochlear compression, not a direct measurement of basilar membrane function. The study measured ear-canal emissions and audiometric thresholds, not a treatment outcome.
Declared interests
The paper states that there are no conflicts of interest.
The easy way to misread this
Do not conclude that this identifies a clinical test for age-related hearing change or a treatment target. The sample was small, the measure was indirect, and after high-frequency hearing thresholds were controlled age was no longer an independent predictor at 3696 Hz or 5207 Hz.