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childrEn and Adults heaRing in noise: individual Differences in the Neurophysiology of Audition

Periodic Reporting for period 1 - EAR-DNA (childrEn and Adults heaRing in noise: individual Differences in the Neurophysiology of Audition)

Reporting period: 2019-01-01 to 2020-12-31

This project was initially designed to improve speech perception in noise in both adult and children listeners with hearing loss. However, due to the pandemic, I have had to reframe this objective, due to the impossibility to recruit and test listeners for almost half the duration of the project. I will present here the final version of the project, as we have had to adapt it to face the pandemic.
In everyday auditory environments, listeners face the challenging task to perceive speech amidst noisy backgrounds. From a psychoacoustical point of view, speech consists of slow amplitude modulations imposed on rapid oscillations of a carrier waveform. Listeners have to process the amplitude fluctuations of target sounds amongst interfering, amplitude-modulated (AM) sounds. For most listeners, the detection of an AM target sound is hindered by the presence of an interfering AM tone in a remote frequency region, a phenomenon known as modulation detection interference (MDI; Sheft & Yost, 1989).
Importantly, MDI increases with the proximity in AM rates between target and masker AMs, leading to an interference of up to 15 dB SPL, with a large inter-individual variability. So far, the neural correlates of MDI have remained unknown. Therefore, the first working package (WP1) of this project was dedicated to the investigation of the neural correlates of modulation detection interference in young, normally-hearing adults. Special interest was paid to their potential relationship to the behavioral performance.
In normally hearing children, the peripheral auditory system is functionally mature by 6 months of age (Werner, 2011). Yet children and adolescents remain more susceptible to noise than adults until around 16 years of age. With noise levels largely exceeding the recommendations of the World Health Organisation, classrooms fall short of providing quiet learning environments. Critically, background noise limits cognitive resources, and may jeopardize academic performance. Therefore, a second working package (WP2) of this project was to evaluate the maturation of speech processing in noise and the mechanisms that contribute to its development in children with normal hearing. Studies specifically investigating stream segregation and selective attention in children suggest that both abilities contribute to speech perception in noise, but remain immature until at least 12 years of age. A second study, conducted online, aimed to investigate the development of selective attention and its contribution to speech perception in noise from childhood to late adolescence.
WP1: neural correlates of modulation detection interference
Twenty-four normally-hearing (mean age: 26 years) adult participants were recruited for a two-part experiment conducted at Ecole Normale Supérieure (Paris). During the first session, an audiological screening was conducted, as well as measures of individual AM detection thresholds. During the second session, neural processing of a 29.7 Hz AM target was investigated in two conditions: without interference (Target alone) and in the presence of the 17.3 Hz interfering AM (Modulated distractor). In each trial, listeners were asked to identify which of the two intervals contained the AM target.

Two neural measures were used as indexes of MDI. The amplitude-modulated following response (AMFR) is a steady-state neural response evoked by the periodicity of amplitude fluctuations in sounds. The awareness related negativity (ARN) reflects the awareness of an auditory object in the presence of an interfering sound stream. Our AMFR data indicate a significant reduction in the amplitude of the neural response to the target AM in the presence of a modulated distractor, as opposed to the target alone condition. Importantly, there was a significant relationship between the amplitude of the ARN and MDI behavioural performance. The results of WP1 will be presented at the 2021 MidWinter meeting of the Association for Research in Otolaryngology

WP2: Development of selective attention from childhood to late adolescence
36 normally-hearing children aged 8 to 18 years were recruited for an online study on selective auditory attention. In the selective attention task, children were presented with two synthesised voices. They were cued beforehand to attend to one of the voices. Additionally, a consonant identification task was presented in three conditions: quiet, one interfering talker, or in a background of speech-shaped noise.

Children’s performance improved from 8 to 16 years, both in terms of their selective attention and speech perception in noise. Interestingly, there is a significant positive relationship between selective attention and perception of speech in noise. Indeed, children who showed better selective attention achieved better consonant identification in noise. The results of WP2 will be presented at national and international conferences, and shared with children, parents, and professionals involved in teaching, remediation and therapy.
The results of WP1, dedicated to the neural correlates of MDI in normally-hearing adults, will have two main impacts on the state of the art in auditory cognitive neuroscience. First, we have shown that MDI entails reciprocal neural interactions between the target and distractor AM channels. This may reflect the involvement of long-distance inhibitory connections between neurons within tonotopic cortical maps. So far, such tonotopic cortical maps have only been observed in animal studies (Read, Winer, & Schreinerr, 2001). Second, we have shown a significant ARN when adult participants successfully detected the AM target. This indexes their ability to segregate two auditory objects. Most importantly, the amplitude of the ARN is a significant predictor of the behavioural performance in the context of MDI. Additional expected results are:

- improving the design of future, neuro-steered, hearing aids. Using machine-learning algorithms, future work will be able to guide participants’ auditory attention based on their neural activity in complex auditory scenes.
- By highlighting the involvement of long-distance, inhibitory connections between neurons within tonotopic cortical maps, we are the first lab to unveil the neurophysiology of spectral maps in adult humans. This will pave the way to a better understanding of the functionality of the human auditory system which has so far only been explored in animal studies.
- In the coming years, the experimental design will be adapted for testing in children and the elderly. As such, it will help further our understanding of the neural correlated of perception of speech in noise across the lifespan.

The results of WP2 will serve as foundation to further our understanding of the protracted development of complex auditory processing.The following impact is expected:
- Improvements in classroom acoustics and teaching strategies. Indeed, the slow maturation of the ability to listen in noise calls for new designs for scholarly environments acoustics. Technologies such as FM systems (i.e. wireless assistive hearing devices), might be considered to improve children' speech in noise abilities.
- By running WP2 as an online experiment, we paved the way towards the possibility of remote psychoacoustical testing. This will allow researchers to reach broader and more diverse samples of participants, hence improving the generalisability of laboratory results.
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