ORIGINAL RESEARCH article
Front. Psychol.
Sec. Perception Science
Sustained Posterior Negativity (SPN) Elicited by Brief (20ms) Symmetrical Stimuli
Provisionally accepted
Giulio Contemori*
Marianna MusaDeniz DemirkapiMartina Passaggi
Carolina Maria Oletto
Luca Battaglini
Marco Bertamini- Universita degli Studi di Padova Dipartimento di Psicologia Generale, Padua, Italy
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Mirror symmetry is detected rapidly, yet it remains unresolved whether its canonical neural signature—the Sustained Posterior Negativity (SPN)—requires extended viewing. We tested stringent temporal conditions for SPN generation by presenting centrally displayed, irregular octagons (symmetric or asymmetric) for 20 ms while preventing premotor preparation via a delayed, trial-wise randomized response mapping. EEG was recorded with a 64-channel montage and preprocessed using a fully scripted, automated pipeline; ERPs were computed from correct trials only. A mass-univariate, cluster-based permutation analysis revealed a mid-latency posterior negativity with the occipitoparietal topography characteristic of the SPN, and a confirmatory analysis within a canonical posterior region of interest converged on the same effect. Behaviorally, participants discriminated symmetry reliably with a modest liberal bias. Fixed-cohort trial subsampling showed that increasing per-condition epochs enhanced statistical detectability without altering amplitude, indicating precision gains rather than changes in the underlying response. No reliable condition differences were observed in earlier sensory components, and there was no compelling hemispheric lateralization. Together, these results demonstrate that brief visual evidence is sufficient to initiate symmetry-selective activity that unfolds over the established SPN time course in the absence of sustained viewing or response preparation. This pattern supports a hybrid account in which a rapid feedforward sweep flags global regularity while recurrent interactions sustain and consolidate the representation, thereby tightening temporal constraints on the neural mechanisms that extract structural order from transient input.
Keywords: Sustained Posterior Negativity (SPN), Evoked related potentials, Symmetry, Visual regularity, Visual Perception
Received: 03 Jul 2025; Accepted: 03 Nov 2025.
Copyright: © 2025 Contemori, Musa, Demirkapi, Passaggi, Oletto, Battaglini and Bertamini. 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: Giulio Contemori, giulio.contemori@unipd.it
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