Age-Related Changes in Speech Recognition Performance-Intensity Functions and Auditory Brainstem Responses

While the mechanisms underlying age-related changes in speech recognition are thought to be multifactorial, cochlear synaptopathy has been proposed as a possible peripheral auditory contributor. Although evidence from animal and human temporal bone studies supporting the presence of age-related cochlear synaptopathy appears compelling, findings from prospective studies in humans have been less conclusive. The goals of this study were to investigate the effect of aging on measures historically used to assess retrocochlear function-speech recognition performance-intensity functions in noise, and high-level auditory brainstem responses (ABR) at two presentation rates, and to examine their association.

Nineteen younger (18 to 36 yrs) and 19 older adults (65 to 81 yrs) with normal audiometric pure-tone averages and clinically present distortion product otoacoustic emissions took part in this study. All test materials were presented to the right ear through insert earphones. Performance-intensity functions were obtained using Northwestern University Auditory Test No. 6 words in multitalker babble, at 6 signal to noise ratios (SNRs) ranging from -5 to +20 dB SNR (noise fixed at 50 dB HL). ABRs were recorded in response to 80 dB nHL clicks presented at a slower rate (11.3/sec) and a faster rate (41.3/sec).

The performance-intensity function slopes were comparable between the younger and older age groups, but older adults needed more favorable SNRs to achieve the same level of performance as their younger counterparts. The electrophysiological finding of lower I/V ABR amplitude ratios in older adults is consistent with an interpretation of cochlear synaptopathy. However, there was no association between the speech recognition performance-intensity function metrics and ABR I/V amplitude ratios, even though full performance-intensity functions were obtained, using low-context monosyllabic words that depend more heavily on peripheral processing.

Results of this study show that aging negatively impacted speech recognition in noise and ABR responses. Although the age-related reduction in ABR wave I/V ratios could be interpreted as evidence of cochlear synaptopathy, age did not differentially impact speech recognition in noise as a function of SNR. In addition, there was no association between the electrophysiological and performance-intensity function metrics. These results add to a growing list of perceptual measures that did not follow the pattern of results predicted by age-related cochlear synaptopathy, despite the expected reduction in ABR wave I/V ratios.