BRIEF RESEARCH REPORT article
Front. Psychol.
Sec. Auditory Cognitive Neuroscience
Volume 16 - 2025 | doi: 10.3389/fpsyg.2025.1685938
The "inverted-U" of cognitive effort across speech rates holds for simple but not complex sentence structures
Provisionally accepted
- Brandeis University, Waltham, United States
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Pupil dilation has become a well-established physiological index of cognitive effort. Here we examined the often-cited finding of an inverted U-shaped function of pupil size across the continuum from highly degraded to clear speech. Unlike the short sentences with simple syntax as used in the original inverted-U demonstrations, 32 young adults recalled sentences with subject-relative embedded clause structures and more syntactically complex object-relative embedded clause structures. Sentences were degraded using time-compression and presented at 10%, 25%, 35% and 100% of their normal playing time selected from a preliminary calibration study. Subject-relative sentences showed an approximately symmetrical inverted U-shaped function across speech rates, but object-relative sentences failed to show the drop in pupil size with normal-rate speech. We conclude that the symmetric inverted U-shaped function of pupil size with increasing speech quality is limited to sentences with simple syntax. We thus offer a more complete picture of the inverted-U than currently in the literature.
Keywords: Pupillometry, effort, Time-compression, Inverted-U, Syntactic complexity
Received: 14 Aug 2025; Accepted: 14 Oct 2025.
Copyright: © 2025 O'Leary, Zavlun, Kinney and Wingfield. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Ryan M. O'Leary, r.oleary@northeastern.edu
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