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PsychophysiologyNeurosciencePeer-reviewed journal article

Changes in aperiodic (1/f slope) activity during a picture-word interference task: Effects of congruency and sequence manipulations

Virginia TronelliiD, Patrycja KałamałaiD, Gabriele GrattoniD, Monica FabianiiD, Máté GyurkovicsiD, Kathy A. LowiD, Maurizio CodispotiiD, Andrea De CesareiiD

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Abstract

Aperiodic neural activity (1/f EEG) has been proposed to reflect the balance between excitatory and inhibitory (E/I) inputs, with steeper spectral slopes reflecting increased inhibition and flatter slopes indicating excitation. This activity is also thought to reflect the temporal coordination of neural firing, offering insights into fundamental brain dynamics. Recent studies have shown that the 1/f slope is sensitive to stimulus onset, characterized by initial inhibitory shifts followed by excitatory rebounds, which may reflect cognitive control mechanisms involved in suppressing distractions and preparing goal-directed responses. However, previous research has relied on fixed temporal windows and insufficient control of ERP contamination, limiting our understanding of rapid control dynamics. Here we used newly developed time-resolved analyses to study 1/f spectral slope modulation during a Picture-Word Interference task, focusing on two canonical cognitive control markers: the Congruency Effect (CE) and Congruency Sequence Effect (CSE). Forty-nine participants categorized pictures while ignoring congruent or incongruent words. Behaviorally, we replicated robust CE and CSE patterns. Spectral slope analyses showed that incongruent trials elicited steeper slopes -- consistent with increased inhibition -- particularly in frontal and central regions, reflecting conflict-related control engagement. Moreover, CSE analyses revealed dynamic slope modulations across frontal, central, and occipital components over time, suggesting control adjustments influenced by previous trial congruency. These results provide the first within-trial time-resolved evidence that aperiodic 1/f EEG activity can track both immediate conflict resolution and cognitive adjustments, offering a temporally sensitive neural marker of cognitive control, albeit with effects that are small in magnitude on average.

In-depth summary

Claude Opus 5.5 · xhigh effort · 8 Nov 2026 · from the full text of version 2 (4 Aug 2026) · CC BY 4.0

Single-cycle wavelet 1/f EEG slopes in 49 young adults are steeper on incongruent picture-word interference trials and track trial sequence, but only three effects survive family-wise correction.

The aperiodic (1/f) EEG slope has been proposed as an index of excitation/inhibition balance, but earlier work linking it to cognitive control often averaged over broad fixed windows, typically longer than 500 ms, and mostly did not account for event-related potential (ERP) contamination. This study removes average ERPs and estimates the slope at each time point with single-cycle wavelets, which the authors present as the first within-trial time-resolved test of the congruency and congruency sequence effects.

Key results

  1. SuggestedSlopes were steeper (more negative) on incongruent than on congruent trials. Only a late central effect and a mid-latency occipital effect survived family-wise error rate (FWER) correction.

    Cluster permutation: central 1141–1258 ms (max|Z| = 3.44, pFWER = .013) and occipital 770–926 ms (max|Z| = 3.03, pFWER = .036). Uncorrected ANOVAs also flagged frontal windows at 480–640, 640–800 and 1120–1280 ms, and the occipital 1120–1280 ms window reversed direction. Aperiodic effects overall had partial ηp² 0.08–0.14. · 3.2.3 Spectral Slope Analysis; 5. Limitations and Future Directions

  2. SuggestedPrevious-trial congruency changed the slope congruency effect in a way that resembled the behavioral congruency sequence effect (CSE). This held after correction only in the occipital component.

    Occipital interaction cluster 516–711 ms (max|Z| = 3.12, pFWER = .031). At 480–640 ms, incongruent trials were steeper after congruent than after incongruent trials (t(48) = 3.13, d = .45), and the congruency effect appeared only after congruent trials (t(48) = 3.57, d = .52). Frontal (160–320, 960–1120 ms) and central (160–320 ms) interactions failed correction; the central one ran opposite. · 3.2.3 Spectral Slope Analysis; 4. Discussion

  3. ShownCompared with the pre-stimulus baseline, the stimulus steepened the slope in all three retained spatial components for most of the post-stimulus epoch.

    Cluster permutation: frontal 8–1160 ms (max|Z| = 5.15) and occipital 8–984 ms (max|Z| = 6.33), both pFWER < .001; central 8–145 ms (max|Z| = 3.58, pFWER = .003) and 203–1238 ms (max|Z| = 6.00, pFWER < .001). Uncorrected window t-tests agreed, except in the last window for the frontal and occipital components. · 3.2.3 Spectral Slope Analysis

  4. ShownIn behavior, the task produced a congruency effect and a CSE in both accuracy and reaction time (RT).

    Accuracy 96.74% incongruent vs 97.53% congruent (F(1,48) = 30.24, ηp² = .39); RT 656.39 vs 641.84 ms (F(1,48) = 16.68, ηp² = .26). RT interaction F(1,48) = 18.33, ηp² = .28: incongruent responses were slower than congruent ones after congruent trials (t(48) = 5.18, d = .74) but not after incongruent trials (t(48) = 1.44, p = .158). · 3.1.1 Accuracy; 3.1.2 Reaction Times

  5. SuggestedIn a supplementary simulation, single-cycle wavelets detected brief slope changes better than fixed fast Fourier transform (FFT) windows, although no estimator reconstructed the imposed slope profile without bias.

    Compared with fixed 500- and 1000-ms FFT windows on short simulated slope changes whose durations matched the corrected empirical effects (Figure S3). The text gives no numerical sensitivity values. · 4. Discussion

Methods, data and reproducibility

EEG from 49 participants in a picture-word interference task was ERP-subtracted, convolved with one-cycle sine/cosine wavelets (2.5 to 25 Hz), and fit with a log-log least-squares slope at each time point, omitting 7.5–15 Hz. Spatial then temporal PCA reduced the data; effects were tested with uncorrected windowed ANOVAs and family-wise-error-controlled sign-flip cluster permutation tests.

  • Scalp EEG (BioSemi ActiveTwo, 64 electrodes at 512 Hz, 56 analyzed) and accuracy/RT from Italian-speaking participants (20 females, mean age 26.27 ± 3.38) in a picture-word interference task · human · n = 49 analyzed (one of fifty tested was excluded)
  • Picture set of animals or vehicles (one or two items, indoor or outdoor), overlaid with the Italian words 'animale' or 'veicolo' · n = 488 pictures
Methods & tools
BioSemi ActiveTwo, E-Prime 2.0 Professional, MATLAB 2022b, EEGLAB 13.6.5, ERPlab 6.1.3, Single-cycle wavelet convolution, Censored regression-based slope estimation (Kałamała et al., 2025), Principal component analysis with Empirical Kaiser Criterion and varimax rotation, Cluster-based sign-flip permutation test, Repeated-measures ANOVA
Code & protocols
https://osf.io/z3qsg
Data & accessions
https://osf.io/z3qsg
Software & environment
Custom MATLAB 2022b preprocessing code using EEGLAB 13.6.5 and ERPlab 6.1.3; E-Prime 2.0 Professional for the task.
Reproducibility gaps
The OSF repository is described as one that 'will be available' and covers data and code for the statistical analyses of section 3.2.3; the text does not say whether raw EEG or the preprocessing and wavelet code will be released.
Limitations (6)
  • The picture-word interference design is not confound-minimized, so feature-integration effects cannot be cleanly separated from control adjustments in the CSE. · stated by the authors
  • Aperiodic effects were small (partial ηp² 0.08–0.14) and only three survived FWER correction. The frontal and central CSE effects and the late occipital reversal are exploratory and may be false positives. · stated by the authors
  • N = 49 may be underpowered, and there was no earlier work to size a time-resolved aperiodic study from. Collapsed concurrent manipulations (stimulus repetition, category repetition, response-stimulus interval) may have diluted the effects. · stated by the authors
  • Only one paradigm was used, and it relies on lexical-semantic processing of concrete stimuli. Whether flanker, Stroop or task-switching tasks show the same dynamics is untested. · stated by the authors
  • Slope changes may partly reflect arousal or motor preparation, given that the congruency effects fall close to response activity. Single-cycle estimates are not instantaneous: wavelet support ranges from about 400 ms at 2.5 Hz to 40 ms at 25 Hz. · stated by the authors
  • The single-cycle estimator is checked only by a supplementary simulation built by the authors. The text reports no head-to-head comparison with fixed-window slope estimates on the empirical EEG. · noted in this summary

Read this if you study aperiodic EEG or cognitive control and want a within-trial, time-resolved spectral slope method that removes ERPs, with corrected and exploratory effects reported separately.

Citations
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FWCI
4.13
Field percentile
top 5%

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