Objective Assessment of Listening Effort: Coregistration of Pupillometry and EEG.
Kelly Miles, Catherine McMahon, Isabelle Boisvert and 4 others
PMID 28752807WHAT IT FOUND
Pupil size grew in normal-hearing participants when speech was less clear and recall was only partial.
Alpha brain activity also changed with less clear speech, but the two measures did not move together within participants, so they are not interchangeable.
Key findings
01In the analysed sample of 19 participants, pupil dilation was 1.49% larger for 6-channel vocoded sentences than 16-channel vocoded sentences, while alpha power change was -30.0% lower for 6-channel than 16-channel.
02Pupil size decreased by -0.05% as true performance increased toward 100%, and pupil size was 1.61% larger for partially correct sentence recall than for correct recall.
03Pupil dilation and alpha power were not significantly correlated within individuals (n = 19, p > .05), including when collapsed across conditions (mean r = .01, SD = .08).
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study tested only 19 young, normal-hearing participants, so it does not show how pupil dilation or alpha power behave in people with hearing impairment. The intended 50% and 80% difficulty levels did not produce the expected performance gap: true performance differed by 18.6% rather than 30%, so the difficulty levels were closer than intended. Alpha power was analysed only at parietal electrodes and in a broad 8 to 12 Hz band, which the authors say may be too restrictive for complex sentence processing in noise. Pupil dilation and alpha power were not correlated, so the study does not show they measure the same aspect of listening effort. The physiological session used fixed signal-to-noise ratios after a shorter behavioural session, and motivation or fatigue may have changed performance between sessions.
The easy way to misread this
Do not conclude that pupil dilation and alpha power are interchangeable clinical measures of listening effort. They were not significantly correlated within individuals, and the study tested only 19 normal-hearing participants in a laboratory speech-in-noise task, not patients.