Bottom-up and top-down neural signatures of disordered multi-talker speech perception in adults with normal hearing

Abstract

In social settings, speech waveforms from nearby speakers mix together in our ear canals. Normally, the brain unmixes the attended speech stream from the chorus of background speakers using a combination of fast temporal processing and cognitive active listening mechanisms. Of >100,000 patient records,~10% of adults visited our clinic because of reduced hearing, only to learn that their hearing was clinically normal and should not cause communication difficulties. We found that multi-talker speech intelligibility thresholds varied widely in normal hearing adults, but could be predicted from neural phase-locking to frequency modulation (FM) cues measured with ear canal EEG recordings. Combining neural temporal fine structure processing, pupil-indexed listening effort, and behavioral FM thresholds accounted for 78% of the variability in multi-talker speech intelligibility. The disordered bottom-up and top-down markers of poor multi-talker speech perception identified here could inform the design of next-generation clinical tests for hidden hearing disorders.

Age-Related Deficits in Electrophysiological and Behavioral Measures of Binaural Temporal Processing

“…Similar to findings from studies that used different electrophysiological measurement techniques (Ross et al, 2007a;Ross, 2008;Ozmeral et al, 2016;Papesh et al, 2017;Ungan et al, 2020), Vercammen et al (2018) showed that the neural encoding of IPD cues tends to be stronger in younger participants compared to older participants and, along with several other studies (Haywood et al, 2015;Undurraga et al, 2016;Vercammen et al, 2018;Parthasarathy et al, 2020), showed that IPM-FR responses tend to be weaker when behavioral detection of the IPD cue is poor. While these previous studies have established that the IPM-FR is likely reflective of behavioral IPD sensitivity, the stimuli previously used to assess behavioral IPD discrimination thresholds were dichotic AM stimuli analogous to those used to elicit the IPM-FR (Haywood et al, 2015;Undurraga et al, 2016;Vercammen et al, 2018;Parthasarathy et al, 2020). Assessing relationships between the IPM-FR and other behavioral measures of binaural temporal processing will determine whether associations between the IPM-FR and behavior can generalize to other stimuli and tasks that assess IPD sensitivity.…”

“…Speech understanding was assessed using a competing digits task where a string of digits spoken by target and competing speakers were presented diotically. As expected, the IPM-FR did not represent a link to speech understanding abilities due to the absence of binaural cues in the behavioral task (Parthasarathy et al, 2020). Therefore, to date, it is unknown whether the IPM-FR is also a neural correlate of functional speech understanding abilities in realistic listening environments that require the use of binaural cues.…”

“…In other words, the electrophysiological measure used by Papesh et al (2017) was better able to reflect the integrity of binaural temporal processing mechanisms that are important for speech understanding in spatialized noise than participant factors such as age and estimated hearing sensitivity. In addition to recently confirming that the IPM-FR reflects behavioral IPD sensitivity, Parthasarathy et al (2020) was the first to examine relationships between IPM-FRs and speech perception. Speech understanding was assessed using a competing digits task where a string of digits spoken by target and competing speakers were presented diotically.…”

Data-driven segmentation of audiometric phenotypes across a large clinical cohort

“…7) suggests that a large percentage of people with bilaterally normal audiograms are coming to the clinic complaining of hearing problems. This adds to the growing literature showing that the audiogram in itself is not sufficient to capture hearing difficulties experienced by people and demonstrates the need for more sensitive tests in the clinic that capture the real-world communication difficulties experienced by patients [36][37][38] .…”

Hemodynamic responses link individual differences in informational masking to the vicinity of superior temporal gyrus

“…In addition, an individual's sensitivity to monaural or binaural temporal fine structure predicts masked speech intelligibility, especially in temporally fluctuating background sound (Lorenzi et al, 2006;Papesh et al, 2017). Intriguingly, this mechanism is thought to be of subcortical origin (Parthasarathy et al, 2020), hinting that tem-poral coding fidelity does not differentially affect listening in EM vs IM backgrounds. However, future work is needed to explore how metabolic need and the fidelity of cortical temporal coding interact.…”