PP516 - Relating Speech-in-Noise Tests with Different Sensory Demands to a Proxy of Cochlear Synaptopathy

To determine whether cochlear synaptopathy contributes to speech-in-noise (SIN) difficulty in normal-hearing listeners, SIN perception should be measured using a task that engages sensory processes impacted by cochlear synaptopathy while minimizing other processes (e.g., cognitive and perceptual) that may influence performance. This study tests this notion by comparing how a proxy of cochlear synaptopathy (compound action potential amplitude) relates to two SIN tests differing in sensory, cognitive, and perceptual demands (AzBio Sentence Lists vs Spatial Release with two maskers). Our results will determine which type of SIN task is more sensitive to cochlear synaptopathy-related deficits in humans.

Summary:

Deficits in understanding speech in background noise – despite clinically defined normal hearing – is suggested to be a perceptual manifestation of inner hair cell-spiral ganglion synapse degradation, known as cochlear synaptopathy. As the existence of cochlear synaptopathy in humans remains inconclusive, it is important to evaluate the tools used to assess both cochlear synaptopathy and speech-in-noise (SIN) deficits. SIN tests widely vary in the sensory, cognitive, and perceptual processes they engage, each uniquely influencing performance. A SIN test that employs top-down cognitive processes may result in compensation of existing sensory deficits, including the putative effects of cochlear synaptopathy. Thus, a SIN test that minimizes non-sensory factors and maximizes reliance on discrete sensory temporal cues should provide a stronger association with proxies of cochlear synaptopathy. To test this hypothesis, the current study compares two SIN measures with different demands to a proxy of cochlear synaptopathy in humans.

We first employed the AzBio Sentence Lists (AzBio), which presents low-context sentences against a continuous 10-talker babble. While the target sentences have low predictability, individual differences in linguistic knowledge and vocabulary could influence performance and minimize use of acoustic temporal cues. Additionally, the multi-talker babble provides more energetic masking than informational, further minimizing reliance on temporal cues to segregate the target speech from the noise. We next employed the Spatial Release with two maskers (SR2) task. This SIN test uses a closed-set corpus with the target presented against two competing talkers, significantly reducing reliance on cognitive factors and emphasizing the use of subtle acoustic temporal cues. Therefore, we predict the SR2 will be more sensitive to the sensory deficits associated with cochlear synaptopathy than AzBio.

Data on adults between 30-50 years of age with thresholds ≤ 25dB HL 0.25-8kHz are actively being collected for this study and will be completed by the February 15^th AAA deadline. At the time of abstract deadline, 31 participants have been tested. AzBio lists are presented in soundfield with the target and maskers co-located at 0° azimuth under fixed signal-to-noise ratios (SNRs) of 0 and -3 dB SPL. Performance is measured as percent correct words repeated out of total possible words in the list. SR2 is administered through the Portable Automated Rapid Testing iPad application with stimuli delivered via circumaural headphones. Co-located and spatially separated (maskers ±45° azimuth) conditions are administered using a progressive tracking masking procedure. Performance is measured as threshold target-to-masker ratio (TMR), where lower TMRs indicate that threshold performance could be achieved at lower SNRs. To assess cochlear synapse function, electrocochleography was collected at a slow (9.1/s) and fast (21.1/s) click rates. Percent change in the peak-to-trough amplitude of the compound action potential (cAP) – as a function of increasing click rates – served as our proxy for cochlear synaptopathy, where larger percent reductions in the cAP amplitude suggests greater synaptic degradation.

Associations between each SIN measure and our proxy of cochlear synaptopathy will be determined through Pearson correlations. The data and corresponding results will inform which SIN tests are appropriate in assessing cochlear synaptopathy-related deficits in humans.