Language
Does noise or hard grammar make listening feel and look effortful?
Open access · cc by · source: Europe PMC
Background noise mainly made listening feel harder, while complex sentence structure mainly made the pupils dilate, suggesting that self-reported effort and pupil size capture different kinds of listening effort.
Study at a glance
- Design
- Human experiment — 2 x 2 within-subject design (noise level +12 vs -6 dB SNR x simple SVO vs complex OVS Danish sentences) in a sentence-picture matching task with pupillometry, effort ratings and span tests
- N
- N=20 · 20 normal-hearing adults tested; one was dropped from the pupil analysis because more than half of their trials needed blink interpolation
- Population
- Normal-hearing Danish-speaking adults aged 19-36 (11 women, 9 men)
- Outcome
- Picture-matching accuracy, subjective effort ratings, and pupil dilation in three time windows; correlations with digit span and reading span
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Key findings
Louder noise produced a large increase in rated difficulty and a small pupil increase early in the sentence, even though accuracy did not differ between noise levels. Complex sentences produced larger, longer pupil dilations after the disambiguating word and during the retention period, but only a small effect on ratings; accuracy on complex sentences was only 57.2-58.1% versus 87.8-93.1% for simple ones. People with higher backward digit span showed larger pupil dilations but rated simple sentences in loud noise as less effortful, fitting the resource hypothesis for pupils and the efficiency hypothesis for ratings.
Methodology
Twenty normal-hearing adults saw a picture of two animals doing something, then heard a Danish sentence in steady speech-shaped noise and judged whether it matched the picture. Sentences were either simple (subject-verb-object) or complex (object-verb-subject), and noise was either mild (+12 dB signal-to-noise ratio) or loud (-6 dB). Pupil size was recorded throughout, listeners rated difficulty after each trial, and they completed digit span and reading span tests of working memory.
Limitations
With only 20 young normal-hearing adults, the individual-difference correlations are fragile and were significant only in one condition; they cannot be generalised to older or hearing-impaired listeners, who are the main target of listening-effort research. Accuracy on complex sentences was close to chance, so some complex-sentence pupil effects may reflect confusion or guessing rather than successful effortful processing. Motivation, which could drive both pupil size and ratings, was not measured, and the reading span task used an older, less sensitive procedure, which the authors note may explain its null correlations.
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