The Autonomic Correlates of Listening Effort

For those with hearing impairment, listening in daily life communication requires excessive mental effort, even when using a hearing aid. This increased daily effort causes fatigue and reduced well-being. In recent years, researchers have utilised physiological measures to quantify listening effort; however, the chosen methods are seldom driven by psychophysiological theories. Despite a considerable number of empirical articles, the evidence in support of the physiological quantification of listening effort is inconclusive.
This thesis employed empirical evidence on autonomic nervous system activity and motivational intensity theory (Brehm, 1989; Wright, 1996), to provide a systematic, inclusive and theory-driven examination of the physiological correlates of listening effort. It was hypothesised that, to avoid wasting essential resources, (listening) effort occurs as a function of (listening) demand while success is possible and the required effort is justified. Listening effort was quantified as myocardial reactivity driven by parasympathetic nervous system withdrawal and sympathetic nervous system activation.
Utilising a systematic and theory-driven approach, three phases of experiments tested the multi-layer predictions of motivational intensity theory in relation to effortful listening. The first phase found empirical evidence for the impact of listening demand on listening effort-driven myocardial sympathetic activation (quantified as pre-ejection period), only while successful speech comprehension was possible. Subjective effort increased alongside myocardial sympathetic activity, but was less limited by the possibility of success. The second phase provided the first evidence for the impact of reward (the importance of success) on listening effort-driven myocardial sympathetic activation (pre-ejection period) in listening tasks with an unclear performance standard. Subjective effort increased, alongside myocardial sympathetic activity, as a function of reward for successful comprehension. The final phase, grounded in the results from phase one and two, provided evidence for a trend of cardiovascular reactivity that partially supported the final hypothesis that an interaction effect between listening demand and reward should affect listening
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effort. However, the final experiment failed to provide evidence for specific cardiovascular reactivity caused by listening effort-related myocardial sympathetic activation as a function of the listening demand- reward interaction.
Overall, this thesis found evidence that, listening effort driven by myocardial sympathetic activation occurs as a function of listening demand while task success is both possible and the required effort is justified by the importance of successful comprehension. No experiment within this thesis found compelling evidence for the impact of either listening demand or the importance of successful comprehension on cardiovascular reactivity influenced by the withdrawal of the parasympathetic nervous system.
This thesis exists to highlight the importance of a holistic evaluation of the physiological correlates of effortful listening guided by psychophysiological theories and motivation science. The experiments in this thesis outline a novel comprehensive approach towards the quantification of listening effort. The results highlight the importance of motivational factors and promote the perspective that both listening demand and fluctuations in the motivation to listen determine listening effort, quantified by sympathetic myocardial activation. In the future, incorporating empirically supported measures of listening effort into audiology might improve the quality of hearing assessments and the calibration of hearing aids.