PP519 - Time-Frequency Analysis of Brain Activity During Listening in Adverse Conditions

Children's and adults' speech perception is often hindered by noise. Their Auditory Late Responses are adversely affected, both in amplitude and latency. However, little is known about cortical oscillations supporting changes in auditory processing based on listening conditions, especially in children. We measured the oscillatory brain rhythms of school-aged children and adults in quiet and noise. Ongoing analyses may show that, under the worst listening conditions, competing noise produces higher loss in brain phase locking in children than adults. Combining ERPs and time-frequency EEG activity analysis might offer a complete picture of the central auditory processing under degraded listening situations.

Summary:

Rationale: Children’s speech perception is known to be especially vulnerable to the effects of noise. The immaturity of their central auditory system results in poor performance in adverse listening conditions. Noise also has a detrimental impact on the Auditory Late Response (ALR), both in amplitude and latency. Literature about brain oscillations related to sound perception in children is scarce; however, it has been shown in adults that noise causes a reduction in neural synchrony, thereby reducing the strength of the cortical oscillation responses. There is currently limited insight into cortical oscillations underpinning differences in auditory processing between children and adults as a function of listening conditions. Analysis of cortical oscillations is warranted to have a better understanding of the auditory processes involved in the cortical responses to auditory stimuli presented in noise.

The present study aimed at investigating the impacts of competitive noise during passive listening on oscillatory brain rhythms in school-age children and adults. We hypothesized that, as the delta, theta, and alpha frequency bands have been related to auditory processes, non-optimal listening conditions would reduce neural synchrony in these specific frequency bands. Furthermore, speech noise such as multi-talker babble, presenting both informational masking (signal degradation due to similarities between masker and stimuli) and energetic masking (signal degradation due to the loudness of masker) qualities could hinder the encoding of auditory stimuli than a mostly energetic masker, such as white noise, to a greater extent in children than in adults.



Design:  Fifteen French-speaking school-aged children (mean ± SD age: 9.9 ± 1.4 years) and fifteen french-speaking young adults (mean ± SD age: 24.5 ± 1.6 years) with normal hearing (i.e., < 20 dB HL at 0.25 to 8 kHz), participated in this study. Each participant underwent a complete peripheral hearing assessment, and their ALRs were recorded with Brain Vision actiCHamp and a 64 active Ag/AgCl electrodes cap. Fourteen randomized blocks of 200 stimuli were presented. Each block consisted of a combination of four stimulus parameters: (1) listening condition – silence or noise; (2) stimulus type – tonal (1 kHz) or verbal (/da/); (3) noise type – white noise or eight-talker babble noise; (4) signal-to-noise ratio – +10, +5 or 0.

Time-frequency analysis was conducted with the signal's convolution and a set of complex Morlet wavelets. Cluster-based permutation tests were then performed using the non-parametric Monte Carlo estimate to obtain the significance probability (p-values) between pairs of listening conditions.

Results:  The analyzes are still ongoing. Time-frequency analysis might reveal that introducing competitive noise causes a greater reduction of neural phase locking in children and adults in most adverse listening conditions (i.e., multi-talker babble). More specifically, analyses could demonstrate a noise-induced decrease of neural synchrony in theta, delta, and alpha frequency bands. Larger differences in brain activity between listening conditions of silence and noise could be found in children compared to adults.



Conclusion: A combined approach using ERPs and time-frequency analyses of EEG activity could provide a more comprehensive picture of the central auditory processing of children and adults in degraded environmental listening conditions.