Do noise and sentence complexity affect listening effort in the same way?

Details

Understanding speech in adverse listening conditions can take effort even when every word is intelligible. Acoustic distortions typically increase that effort, but linguistic features such as syntactic complexity also matter.

Researchers recorded pupil dilation and subjective effort ratings from 20 normal-hearing participants performing a sentence comprehension task. Sentences were either syntactically simple, with a subject-first structure, or complex, with an object-first structure. They were presented at two background noise levels, both corresponding to high intelligibility. Digit span and reading span tests assessed individual differences in working memory capacity (WMC).

Subjectively rated effort was mostly affected by noise level and less by syntactic complexity. Conversely, pupil dilation increased with syntactic complexity but showed only a small effect of noise level. Participants with higher WMC showed increased pupil responses in the higher-noise condition but rated sentence comprehension as less effortful than participants with lower WMC.

The results indicate that pupil dilation and subjective effort ratings represent different aspects of effort, and that effort can vary even when speech intelligibility is high.