Listening effort measurement by pupillometry under dual-task paradigms: the effect of auditory spectral resolution

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PURPOSE: This study evaluated the relationship between auditory spectral resolution and listening effort using cochlear implant simulations in 21 normal-hearing participants. METHODS: In a dual-task paradigm, participants repeated noise-vocoded sentences to 4, 6, 8, and 12 channels, as well as everyday normal speech, while performing a secondary rhyme-judgment task. Listening effort was measured via secondary-task reaction time and pupil dilation. RESULTS: Decreased spectral resolution increased both reaction time and pupil size, indicating greater effort. Reaction time increased significantly only in the most degraded conditions (4 and 6 channels), whereas pupil dilation increased across all degraded conditions compared to intact speech. Speech intelligibility, although affected by degradation, did not predict either of the effort measures. The weak correlation between reaction time and pupil size suggests they capture related but distinct aspects of listening effort. CONCLUSION: These findings highlight the multidimensional nature of listening effort, demonstrating that physiological measures can reveal increased cognitive load even when behavioral performance is unaffected. Combining these measures is crucial for a comprehensive assessment of the cognitive consequences of perceiving degraded speech.