Cited by 716Neural dynamics and brain functionPhilosophy and Theoretical ScienceVisual perception and processing mechanisms

The DOI matches its Crossref record; 49 of the 49 references it cites were found in a registry or an index; none of the 23 sources its claims cite is checked for support yet.

Synchronization of Neural Activity across Cortical Areas Correlates with Conscious Perception

Open access
Melloni, Lucia, Molina, Carlos, Pena, Marcela, Torres, David, Singer, Wolf, Rodriguez, Eugenio·2007·The Journal of Neuroscience

Abstract

Subliminal stimuli can be deeply processed and activate similar brain areas as consciously perceived stimuli. This raises the question which signatures of neural activity critically differentiate conscious from unconscious processing. Transient synchronization of neural activity has been proposed as a neural correlate of conscious perception. Here we test this proposal by comparing the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceived induced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillations before the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the early transient global increase of phase synchrony of oscillatory activity in the gamma frequency range.

Overview

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TL;DR

In a masked-word delayed matching-to-sample EEG study, consciously perceived and unperceived words produced similar local gamma activity, but only perceived words triggered a transient long-distance synchronization of gamma oscillations across cortical areas. The authors propose this early global phase synchrony as a critical event mediating access to conscious perception.

Key findings

  • Visible words were correctly classified 94.5% of the time (mean d′ = 3.85), whereas invisible words dropped to chance (52.2%; mean d′ = 0.16); reaction times were shorter for visible than invisible words (923 vs 1418 ms).
  • Both visible and invisible words increased local gamma oscillations, but only visible words induced transient long-distance gamma phase synchrony at 50–57 Hz from 80 to 130 ms after sample-word presentation (F(1,14) = 5.041; p = 0.044), with no concurrent difference in gamma amplitude or ERPs.
  • Only visible words later produced a frontocentral P3a-like positivity from 130 to 430 ms, peaking at 240 ms (F(1,14) = 37.766; p = 0.00002; 2.3394 µV difference), enhanced frontal theta (5–6 Hz) during maintenance, and increased gamma power and phase synchrony before test-word presentation (synchrony: F(1,14) = 11.803, p = 0.005; power: F(1,14) = 8.006, p = 0.015).
  • In a separate unconscious priming experiment (n = 20), invisible primes still produced a 15 ms congruent-versus-incongruent reaction-time effect (F(1,19) = 8.981; p = 0.007), indicating deep processing without awareness.

Methods

  • Experiment 1: 15 healthy right-handed native Spanish speakers performed a two-alternative forced-choice delayed matching-to-sample task (320 trials); a 33 ms sample word was rendered visible or invisible by mask luminance, followed 533 ms later by a test word, with control conditions to subtract mask-stream responses.
  • Experiment 2: 20 subjects performed an unconscious semantic priming task with the same word set and masks; invisible primes were semantically congruent or incongruent with targets.
  • EEG was recorded from a 64-electrode geodesic sensor net at 1000 Hz. Analyses included ERPs, time-frequency power, and phase-locking value (PLV) for phase synchrony, with permutation tests and within-subject ANOVAs; topographic synchrony used a conservative threshold of p < 0.00005.

Limitations

  • The paper states that the transient long-distance synchronization is not entirely compatible with models predicting sustained activity for conscious stimuli, because synchrony lasted about 100 ms but reached significance only for about 50 ms.
  • The paper states that the mechanism by which long-distance synchronization affects subsequent cognitive processes remains to be clarified, and whether early synchronization itself is phenomenal awareness or whether awareness emerges from later processes is unresolved.
  • The paper notes that precise onset of enhanced theta could not be determined because long windows were needed for low-frequency oscillations; it also reports that luminance and volume-conduction confounds were addressed by control subtractions and phase-lag analyses, though these remain methodological considerations evident from the design.

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Integrity signals

Registry

Crossref · 10.1523/jneurosci.4623-06.2007

Cites

49 of 49 references verified0 citation errors · 0 not checkable

Statistics

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Verification

Claims the paper makes

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Show all 71 claims

  • It may state two separate claims as one. 25
  • Probably not a substantial claim. 10
33 of 33
  • The paper relies on this without support.

    The EEG response to the masking stimuli is equivalent in experimental and control conditions, so subtracting control from experimental traces isolates the response to the sample word.

    “This design enabled us to isolate the response to the sample word by subtracting the response elicited by the masking stimuli.”
  • The paper relies on this without support.

    The filter that eliminated the continuous 50 Hz AC component kept the biological 50 Hz signal intact.

    “a filter was designed that eliminated only the continuous 50 Hz (AC) component but kept the biological 50 Hz signal.”
  • The paper relies on this without support.

    Subjective report of word visibility is a valid index of conscious perception.

    “Only words reported as perceived induced”
  • The paper relies on this without support.

    The delayed matching to sample task involves language processing.

    “which agrees with the fact that the task involves language processing.”
  • The paper relies on this without support.

    Enhanced synchronization can be mimicked by volume conduction if it occurs with zero phase lag.

    “Enhanced synchronization can be mimicked by volume conduction if it occurs with zero phase lag.”
  • The paper relies on this without support.

    If observed synchronization were attributable to activation or inactivation of one or several generators, it should show up as a difference in induced gamma activity or ERPs between experimental conditions.

    “if the observed synchronization were attributable to activation or inactivation of one or several generators, it should show up as a difference in the induced gamma activity or in the ERPs between experimental conditions.”
  • The paper relies on this without support.

    Synchronization caused by volume conduction must occur with zero phase difference between electrodes.

    “synchronization caused by volume conduction must occur with zero phase difference between electrodes.”
  • The paper relies on this without support.

    Phase synchronization caused by volume conduction should exhibit a distance-dependent gradient on the scalp.

    “phase synchronization caused by volume conduction should exhibit a distancedependent gradient on the scalp”
8 of 8

Claims other papers make about this one

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Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Test-related gamma increase is placed before and after test presentation

    Minor

    The abstract places the increase in gamma power and phase synchrony before the test word, but the results place both measured increases after its presentation.

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Citations

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Research works printed but not linked: 2

  1. Burgess, 1999, Methodological advances in the analysis of event-related desynchronization data: reliability and robust analysis, Vol 6, 139
  2. Wolfe JM (1999) in Fleeting memories: cognition of brief visual stimuli, Inattentional amnesia, ed Coltheart V (MIT, Cambridge, MA), pp 71–91.

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Metadata

Authors
Melloni, L., Molina, C., Pena, M., Torres, D., Singer, W., & Rodriguez, E.
Affiliations
  • Radboud University Nijmegen (NL)
  • Pontificia Universidad Católica de Chile (CL)
  • Goethe University Frankfurt (DE)
Venue
The Journal of Neuroscience
Published
2007-03-14
Volume
27
Issue
11
Pages
2858-2865
ISSN
  • 0270-6474 (ISSN-L)
  • 1529-2401
OpenAlex
W1983939506
Cited by
716
References
49
Citations by year
2026: 12 · 2025: 16 · 2024: 21 · 2023: 23 · 2022: 39 · 2021: 31 · 2020: 31 · 2019: 50 · 2018: 24 · 2017: 49 · 2016: 40 · 2015: 45 · 2014: 52 · 2013: 36 · 2012: 44
FWCI
27.31
Type
journal article
Language
en
Open access
Locations
  • Journal of Neuroscience (publishedVersion, cc-by-nc-sa)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • Americanae (AECID Library) (submittedVersion, other-oa)
  • LA Referencia (Red Federada de Repositorios Institucionales de Publicaciones Científicas) (submittedVersion, other-oa)
Topics
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Neural dynamics and brain function
  • Social Sciences › Arts and Humanities › Philosophy › Philosophy and Theoretical Science
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Visual perception and processing mechanisms
Keywords
conscious perception, subliminal perception, neuronal synchronization, gamma oscillations, phase synchronization, theta oscillations, P300, event-related potentials, delayed matching-to-sample, unconscious processes
MeSH terms
Adult, Cerebral Cortex, Consciousness, Cortical Synchronization, Female, Humans, Male, Neurons, Perception, Psychomotor Performance, Reaction Time

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