Pupil responses indicate task-relevance and (unsuccessful) inhibition of background sounds during a dual, continuous listening task

Auditory attention can be voluntarily directed towards a sound source or automatically captured by background sounds, which may be either relevant, such that the listener shifts their attention to them, or irrelevant such that the listener tries to ignore or inhibit them. The ability to switch focus to a relevant sound source while inhibiting an irrelevant one requires attentional control and is crucial for navigating busy auditory scenes. Objective measures of attentional control could be beneficial in clinical contexts, such as fitting hearing aids. In a dual-task paradigm, we investigated whether pupil responses reflect relevance-dependent attentional selectivity. Participants with self-reported normal hearing (N = 21, Age: 27 to 66 years, pure tone average: -4 to +26 dB HL) listened to continuous speech from the front (primary task) while background sounds, consisting of cue names followed immediately by two-digit numbers, were presented from the left and right. The participant was told that one side, either right or left, was relevant and the other, irrelevant. The secondary task involved memorizing and later recognizing numbers from the relevant side. We observed increased pupil responses to sounds from the relevant side compared to the irrelevant side, indicating selectivity. Exploratory analysis showed that participants who exhibited stronger selectivity recognized more numbers correctly. Interestingly, pupil responses did not differ between hits and misses, but a stronger response to stream confusions versus correct rejections was found, suggesting that participants were more challenged by inhibiting irrelevant sounds than shifting attention to relevant sounds. In sum, our findings demonstrate that pupillometry provides valuable insights into attentional control abilities.