Characterising time-on-task effects on oscillatory and aperiodic EEG components and their co-variation with visual task performance

Kopčanová, Martina; Thut, Gregor; Benwell, Christopher S.Y.; Keitel, Christian · 2025 · Crossref

DOI: 10.1162/imag_a_00566

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Summary

This study investigates whether systematic time-on-task (ToT) trends in electroencephalography (EEG) activity confound observed brain-behavior relationships, specifically regarding visual task performance. Research often assumes that correlations between neural oscillations and behavior arise from stochastic, trial-by-trial fluctuations. However, both brain activity and performance metrics like reaction time can exhibit deterministic drifts over the duration of an experiment. The authors aimed to determine if ToT effects explain variability in the relationship between oscillatory brain activity and behavioral outcomes, including response speed, accuracy, and decision confidence. Thirty-six participants performed a 900-trial two-alternative forced-choice visual discrimination task, rating their confidence in each decision. EEG was recorded using a 32-channel system. The researchers analyzed pre- and post-stimulus spectral power (1–40 Hz) and aperiodic components across five experimental blocks. They employed spectral parameterization to isolate periodic (oscillatory) from aperiodic (broadband) activity, ensuring that observed effects were not artifacts of the latter. Statistical analyses included cluster-based permutation tests for spectral differences and hierarchical multiple regression to assess whether controlling for trial order (ToT) abolished brain-behavior correlations. Behavioral results indicated that accuracy and reaction times improved significantly from the first block to subsequent blocks, suggesting practice effects, while confidence ratings remained stable. EEG analysis revealed that ToT effects were primarily localized to the alpha band (8–13 Hz). Alpha power increased and peak alpha frequency decreased linearly over time in both pre- and post-stimulus periods. Crucially, these changes persisted after controlling for aperiodic contributions, which showed no significant ToT effects. Beta band power also increased but was spatially restricted to frontal and parieto-occipital regions. The study found that ToT effects in alpha frequency and power significantly predicted single-trial reaction times. However, when trial order was included as a covariate in regression models, the relationship between alpha activity and reaction time was effectively removed. In contrast, ToT did not account for EEG signatures predicting decision confidence. These findings demonstrate that alpha-band brain-behavior relationships can be spurious, driven by shared time-dependent drifts rather than functional coupling. By dissociating these confounded relationships from those that remain after accounting for ToT, the study clarifies the functional role of alpha oscillations in visual perception and highlights the necessity of controlling for non-stationarities in EEG research.

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• neuro workload indices

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• Empirical Findings: physiological data