Probing the Bottleneck of Awareness Formed by Foveal Crowding: A Neurophysiological Study

Ziv Siman-Tov, Maria Lev, Uri Polat

Research output: Contribution to journalArticlepeer-review


Crowding occurs when an easily identified isolated stimulus is surrounded by stimuli with similar properties, making it very difficult to identify. Crowding is suggested as a mechanism that creates a bottleneck in object recognition and awareness. Recently, we showed that brief presentation times at the fovea resulted in a significant crowding effect on target identification, impaired the target’s color awareness, and resulted in a slower reaction time. However, when tagging the target with a red letter, the crowding effect is abolished. Crowding is widely considered a grouping; hence, it is pre-attentive. An event-related potential (ERP) study that investigated the spatial–temporal properties of crowding suggested the involvement of higher-level visual processing. Here, we investigated whether ERP’s components may be affected by crowding and tagging, and whether the temporal advantage of ERP can be utilized to gain further information about the crowding mechanism. The participants reported target identification using our standard foveal crowing paradigm. It is assumed that crowding occurs due to a suppressive effect; thus, it can be probed by changes in perceptual (N1, ~160 ms) and attentive (P3 ~300–400 ms) components. We found a suppression effect (less negative ERP magnitude) in N1 under foveal crowding, which was recovered under tagging conditions. ERP’s amplitude components (N1 and P3) and the behavioral proportion correct are highly correlated. These findings suggest that crowding is an early grouping mechanism that may be combined with later processing involving the segmentation mechanism.

Original languageEnglish
Article number169
JournalBrain Sciences
Issue number2
StatePublished - 7 Feb 2024

Bibliographical note

Publisher Copyright:
© 2024 by the authors.


Funding was provided by the Israel Science Foundation (Grant No. 2494/21, UP).

FundersFunder number
Israel Science Foundation2494/21


    • EEG
    • awareness
    • crowding
    • grouping
    • masking
    • pop-out
    • tagging
    • visual processing


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