Envelope following responses predict speech-in-noise performance in normal-hearing listeners

Abstract

Permanent threshold elevation after noise exposure or aging is caused by loss of sensory cells; however, animal studies show that hair cell loss is often preceded by degeneration of the synapses between sensory cells and auditory nerve fibers. Silencing these neurons is likely to degrade auditory processing and may contribute to difficulties understanding speech in noisy backgrounds. Reduction of suprathreshold ABR amplitudes can be used to quantify synaptopathy in inbred mice. However, ABR amplitudes are highly variable in humans, and thus more challenging to use. Since noise-induced neuropathy preferentially targets fibers with high thresholds and low-spontaneous rate, and because phase locking to temporal envelopes is particularly strong in these fibers, measuring envelope following responses (EFRs) might be a more robust measure of cochlear synaptopathy. A recent auditory model further suggests that modulation of carrier tones with rectangular envelopes should be less sensitive to cochlear amplifier dysfunction and therefore a better metric of cochlear neural damage than sinusoidal amplitude modulation. Here, we measure performance scores on a variety of difficult word-recognition tasks among listeners with normal audiograms and assess correlations with EFR magnitudes to rectangular vs. sinusoidal modulation. Higher harmonics of EFR magnitudes evoked by a rectangular-envelope stimulus were significantly correlated with word scores, whereas those evoked by sinusoidally modulated tones did not. These results support previous reports that individual differences in synaptopathy may be a source of speech recognition variability despite the presence of normal thresholds at standard audiometric frequencies.

The Speech Envelope Following Response in Normal and Hearing Impaired Listeners

“…In recent work from our lab, the EFR to a rectangular stimulus was found to be a good predictor of HP speech reception in SWN in normal hearing listeners (Mepani et al, 2021). This stimulus was not only designed to boost synchrony to the stimulus envelope of midbrain nuclei to the stimulus envelope, but also to enhance differences based on cochlear synaptopathy, while being relatively insensitive to HF hearing loss.…”

Cutting Through the Noise: Noise-Induced Cochlear Synaptopathy and Individual Differences in Speech Understanding Among Listeners With Normal Audiograms

“…Three experiments found that performance on a modified, difficult version of the QuickSIN correlated with ABR measures [one experiment in Grant et al (2020); one in Mepani et al (2020)] or EFRs [one in Mepani et al (2021)].…”

“…The three studies reporting significant relationships between sentence identification performance and CS proxies also employed stimuli to elicit electrophysiological responses that may be better suited to identify CS-related AN degeneration than those utilized by many other human studies [see Table 2 in Supplemental Digital Content 1, http://links.lww.com/EANDH/A935; Bharadwaj et al 2019; Vasilkov et al 2021; see discussions in Grant et al (2020); Mepani et al (2020); and Mepani et al (2021) for further details]. These findings thus highlight the importance of developing both electrophysiological proxies of CS and speech perception tasks in difficult listening conditions that are sensitive to CS.…”

The variability in potential biomarkers for cochlear synaptopathy after recreational noise exposure

“…Garrett et al (2020) observed a strong correlation between a rectangularly amplitude modulated (RAM) EFR magnitude and speech intelligibility of young and older normal-hearing and hearing impaired subjects. In this regard, Mepani et al (2021) found a weak but significant correlation between RAM-EFR magnitude and word recognition scores of normal-hearing listeners. However, other studies did not confirm these findings, e.g.…”