Alfandari Menase, Defne
(2022)
Motivation and fatigue effects in pupillometric measures of listening effort.
PhD thesis, University of Nottingham.
Abstract
Listening effort and fatigue are common among individuals with hearing impairment, although within hearing sciences the relationship between effort and fatigue is not fully understood. The objective measurement of listening effort has commonly involved pupillometry in combination with the speech-in-noise paradigm, where the baseline pupil diameter (BPD) is used as a reference point, and the mean and peak pupil dilation (MPD and PPD) as indices of listening effort. Research to quantify listening effort to date has mostly investigated effort as a function of listening demands. Recent research has shown a correlation between PPD and daily-life fatigue. Furthermore, monetary incentives have been shown to increase the PPD, suggesting that listening demands alone are insufficient to explain variation in PPD. How motivation and fatigue influence the pupil metrics remains unclear.
Frameworks and models of listening effort and listening-related fatigue postulate that larger previous load should result in larger subsequent fatigue. Fatigue manifests as a reluctance to mobilize further effort, particularly when listening conditions are difficult, and when expected rewards are low. In this study we experimentally investigated the interactive influences of task-induced fatigue, motivation, and listening demands on the BPD, MPD, and PPD in the speech-in-noise task. Participants completed a speech-in-noise task of 30-40 minutes without any breaks (“load sequence”) in 3 experiments. Pre- and post- load sequence listening effort was assessed under varying signal-to-noise ratios (SNRs; listening demands), monetary incentives (motivation level; Experiment 1), and magnitudes of load sequence (fatigue level; Experiment 2) in normal hearing adults. In adults with impaired hearing (Experiment 3), pre- and post-load sequence listening effort was investigated when wearing hearing aids that were described as novel technology (implied reward; high motivation) and conventional technology (no reward; low motivation). In addition to the pupil metrics, need for recovery, self-reported effort, estimated performance, and tendency to quit listening were assessed.
In Experiment 1 and 2, there was a consistent decline in BPD from pre- to post- load sequence, independent of listening demands, monetary incentives, and load sequence magnitude. These results indicate declines in arousal with time-on-task. Replicating earlier research, the MPD scaled with listening demand. Crucially, the pre- to post- load sequence change in PPD was larger with smaller monetary incentives, and larger with larger load sequence magnitude. This result is in line with the conceptualization that larger previous effort results in larger mental fatigue. Furthermore, in a state of fatigue, the mobilization of effort depends on the willingness to perform well. In Experiment 3, we have shown that in adults with impaired hearing, need for recovery and load sequence may interactively influence the BPD and PPD. In all experiments, there was no evidence for a change in speech reception performance, self-reported effort, estimated performance, or tendency to quit listening from pre- to post-load sequence, as a function of load sequence magnitude, monetary incentives, or hearing aid descriptions. This is in line with the understanding that the PPD reveals valuable information that is not captured through traditional speech recognition tests or self-report measures.
Overall, by demonstrating the direct influence of previous load sequence on the PPD, these studies suggest that listening-related fatigue may influence listening effort. Furthermore, this influence may be modulated by motivational factors. Thus, models that explain listening effort and listening-related fatigue need to consider the interactive influence of motivation and fatigue on listening effort.
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