The Relation Between Sustained Listening Under Difficult Conditions and Behavioral, Subjective, and Physiological Indicators of Fatigue

This study investigated whether sustained listening effort (sLE) contributes to measurable changes in fatigue, defined here as a decline in performance and/or motivation to sustain effort over time and to fatigue-related sleepiness, defined as a physiological state indexed by spontaneous pupil fluctuations. We further evaluated whether the Pupil Unrest Index (PUI) can serve as an objective marker of these processes. Twenty young adults with normal hearing completed a sustained listening task under speech-on-speech masking while simultaneously performing a secondary memory task, tested across four acoustic processing conditions. PUI increased from pre- to posttest in most participants, with the largest rise in the most difficult (unprocessed colocated) condition. Subjective fatigue ratings also increased across sessions, though without systematic differences between conditions. Behavioral results showed sequence effects: performance declined in intermediate conditions, whereas it remained stable in the easiest and hardest conditions, suggesting that both fatigue and motivational regulation shaped outcomes. Together, these findings demonstrate that sLE is associated with increased subjective fatigue and fatigue-related sleepiness. They further support the PUI as a promising objective physiological marker of fatigue-related sleepiness associated with sLE, complementing subjective and behavioral assessments.