Effects of age on psychophysical measures of auditory temporal processing and speech reception at low and high levels

Samuele Carcagno,Christopher J Plack

doi:10.1016/j.heares.2020.108117

Samuele Carcagno, Christopher J Plack

Open Access

https://doi.org/10.1016/j.heares.2020.108117

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Abstract

Age-related cochlear synaptopathy (CS) has been shown to occur in rodents with minimal noise exposure, and has been hypothesized to play a crucial role in age-related hearing declines in humans. It is not known to what extent age-related CS occurs in humans, and how it affects the coding of supra-threshold sounds and speech in noise. Because in rodents CS affects mainly low- and medium-spontaneous rate (L/M-SR) auditory-nerve fibers with rate-level functions covering medium-high levels, it should lead to greater deficits in the processing of sounds at high than at low stimulus levels. In this cross-sectional study the performance of 102 listeners across the age range (34 young, 34 middle-aged, 34 older) was assessed in a set of psychophysical temporal processing and speech reception in noise tests at both low, and high stimulus levels. Mixed-effect multiple regression models were used to estimate the effects of age while partialing out effects of audiometric thresholds, lifetime noise exposure, cognitive abilities (assessed with additional tests), and musical experience. Age was independently associated with performance deficits on several tests. However, only for one out of 13 tests were age effects credibly larger at the high compared to the low stimulus level. Overall these results do not provide much evidence that age-related CS, to the extent to which it may occur in humans according to the rodent model of greater L/M-SR synaptic loss, has substantial effects on psychophysical measures of auditory temporal processing or on speech reception in noise.

Highlights

Presbycusis, the decline of hearing abilities with age, is one of the most common chronic conditions in older adults (Lin et al, 2011)
The primary aim of the current study was to test the hypothesis that age-related deficits in the processing of supra-threshold sounds are greater in conditions that are thought to rely on lowand medium-spontaneous rate (L/M-SR) fibers for stimulus coding: namely stimuli presented at a high SPL, and within a noise background
As noted by Hickox et al (2017), the association between the spontaneous rates of auditory-nerve fibers and their thresholds, which have been observed for a number of mammalian species, were not observed in a study on a non-human primate species

Summary

Introduction

Presbycusis, the decline of hearing abilities with age, is one of the most common chronic conditions in older adults (Lin et al, 2011). Noise exposures titrated to cause only temporary threshold shifts, with little outer hair cell (OHC) damage, have been shown to result in a permanent loss of synapses between IHCs and auditory nerve fibers in young CBA/CaJ mice (Kujawa and Liberman, 2009). This synaptic disconnection has been shown to affect mostly auditory-nerve fibers with low and medium spontaneous rates (L/M-SR fibers) with rate-level functions extending to high levels, beyond the saturation point of high spontaneous rate (H-SR) fibers (Furman et al, 2013). Noise-induced CS has been observed in a range of rodent species other than CBA/CaJ mice (see Hickox et al, 2017, for a review), and in primates (Valero et al, 2017)

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