Previous studies indicated that the pupil dilation response to speech perception, associated with listening effort, is altered in individuals with hearing loss. Here, we aimed to assess the relationship between hearing loss and autonomic nervous system activity using cardiovascular and skin-conductance measures as well as pupillometry. We measured respiratory sinus arrhythmia (RSA) related changes in heart-rate variability, pre-ejection period of the left ventricle of the heart (PEP), skin conductance level (SCL) and the peak pupil dilation response during listening. RSA is sensitive to changes in parasympathetic activity, PEP and SCL are influenced by sympathetic activity, and the pupil response is influenced by both autonomic nervous system components.

Data of 125 participants were analysed (mean age 58 years, range 37-72 years). Pure-tone hearing thresholds (weighted pure-tone average of both ears at 500, 1000, 2000, and 4000 Hz, taking into account asymmetrical hearing loss) ranged from normal hearing to moderate levels of hearing loss. Participants performed adaptive speech reception threshold (SRT) tests targeting either 20%, 50% or 80% sentence intelligibility. Target sentences were pronounced by a female talker and masked with male interfering speech. Frequency-specific amplification of the stimuli was applied to increase audibility. Physiological measures (see above) and subjective ratings of effort, performance, difficulty and giving up were collected. We applied linear mixed effect models to test the effect of intelligibility (3 levels) and hearing loss on the dependent measures, controlling for age, sex, BMI, and tinnitus complaints.

More severe hearing loss was associated with worse SRTs and smaller peak pupil dilation. The peak pupil dilation and PEP reactivity were largest for 50% intelligibility as compared to both 20% and 80% intelligibility. No effect of intelligibility or hearing loss was observed on RSA or SCL. Intelligibility influenced all subjective ratings in the expected direction. Also, more severe hearing loss was associated with higher effort ratings, particularly in the 80% intelligibility condition.

The results replicated previous effects of intelligibility and hearing loss on the pupil dilation response. Also, changes in intelligibility level did increase sympathetic activity as reflected by PEP, specifically in the 50% intelligibility condition. RSA and skin conductance measures were not sensitive to hearing difficulties evoked by the current conditions in this sample. Speculatively, the associations between hearing loss and the pupil response might be related to more general effects of fatigue or motivation, as the subjective ratings confirmed relatively effortful listening, especially for individuals with more severe hearing loss.