Repeated effortful listening may be associated with higher levels of experienced fatigue in hearing-impaired listeners compared to their normal-hearing peers. Furthermore, such hearing-related fatigue may include restrictions in engagement in work and withdrawal from major social roles. Mental fatigue resulting from effortful listening is taxing for the attention and cognitive resources required to understand speech. The increased allocation of cognitive resources associated with this heightened 'effort' may also negatively impact their ability to perform other mental operations.

A balance of parasympathetic and sympathetic nervous system activity might explain this effect. People with more hearing problems have lower levels of parasympathetic activity. They thus had a poorer ability to 'unwind' or recover from the stress related to their long-lasting hearing problem.

The degradation of spectral resolution and increased listening effort to understand speech was correlated with pupil diameter. Pupil response reflects the mechanism where the allocation of cognitive resources decreases as a function of speech intelligibility. Previous results suggest that the pupil response reflects the storage of the information (for rehearsal) and the demand for explicit processes. Therefore, the pupil response might be related to working memory processes. An index of listening effort could complement current clinical assessment tools such as pure-tone audiometry and speech-in-noise tests.

Overall, the 'tonic' pupil size reflects the general arousal level of the participants. Moreover, the phasic changes in pupil size react to the stimuli index of cognitive or emotional processes. Therefore, an alternative interpretation of the current results is that the more significant pupil response at lower intelligibility levels reflected an emotional response (e.g., increased anxiety or stress) to the greater task difficulty. The pupil diameter follows an inverted U - shaped curve in relation to listening comprehension across a wide range of signal-to-noise ratio efforts. The most prominent pupil dilation occurs when the intelligibility is around 50% correct performance.

The results indicate a more significant effect of parasympathetic inhibition on the pupil dilation response of listeners with better hearing acuity and a relatively high parasympathetic activity in those with worse hearing acuity. Nevertheless, they failed to explain such differences, and there is a need for more research into this topic.