Seeing listening in the eyes: Examining the effects of light level and fatigue on pupil dilation during a speech-in-noise task

Author: Jennifer Baldock

Baldock, Jennifer, 2022 Seeing listening in the eyes: Examining the effects of light level and fatigue on pupil dilation during a speech-in-noise task, Flinders University, College of Nursing and Health Sciences

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Listening effort can be defined as the cognitive processing that is required to attend to, and understand an auditory message. Challenging listening conditions are encountered frequently throughout the average day and can increase the listening effort that is required of individuals, particularly for those with hearing loss. Excessive listening effort can lead to fatigue which may lead to communication breakdown and withdrawal, and can have negative consequences for occupational, social, and psychological wellbeing. To date, there is no clinically available measure of task-specific listening effort.

Pupil dilation is one physiological measure of listening effort that has received significant attention in research settings. This has resulted in a substantial body of literature describing task-evoked pupil response (TEPR) outcomes during auditory tasks, for individuals with and without hearing loss. It might be practical to use this measure in clinical audiology. This thesis provides an original contribution to knowledge regarding the use of TEPRs to measure listening effort and may have implications for continuing research in the area as well as potential clinical applications of TEPRs.

The empirical studies that make up this thesis were driven by gaps in the literature regarding two factors that may affect TEPRs during a speech in noise task: light level and fatigue. These factors were examined across three studies involving 36 participants.

Study 1 provides evidence that light level does affect TEPRs in a speech in noise task and that light level and task difficulty interact in their effect on TEPRs. A novel approach for using trial-level pupil data in the quantification of listening effort was also tested and described.

In Study 2, the potential mechanisms behind the relationship between light level and TEPRs were examined via mediation analyses. These analyses revealed that baseline pupil diameter partially mediated the relationship between light level and TEPRs by suppression (i.e., inconsistent mediation). This was the first study to provide evidence of this effect.

Study 3 provided preliminary evidence which suggested that there may have been an effect of time on task in the trial level TEPRs across the test session and within each condition. This may be consistent with reduced physiological arousal because of fatigue during the speech in noise task. This was supported by subjective fatigue and task engagement reports but was not supported by performance measures.

TEPR based measures of listening effort are a candidate for implementation in clinical audiology and may improve evaluation of clients’ auditory difficulties and rehabilitative outcomes. While there are no current protocols for using TEPRs in clinical audiology, technological and statistical advances, and increased understanding of TEPRs may enable this implementation in the future. The research reported in this thesis contributes to the growing body of work examining and enhancing understanding of TEPRs as a measure of listening effort.

Keywords: Listening effort, task-evoked pupil response, hearing, pupil dilation, fatigue, time-on-task, speech-in-noise

Subject: Audiology thesis

Thesis type: Doctor of Philosophy
Completed: 2022
School: College of Nursing and Health Sciences
Supervisor: Dr Sarosh Kapadia