September 2021
Volume 21, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2021
More crowded, less numerous: Crowding reduces the number of perceived items in numerosity perception
Author Affiliations & Notes
  • Miao Li
    University of Lille
    KU Leuven
  • Bert Reynvoet
    KU Leuven
  • Bilge Sayim
    University of Lille
    University of Bern
  • Footnotes
    Acknowledgements  This research is supported by a joint doctorate KU Leuven and I-SITE ULNE grant to Bilge Sayim and Bert Reynovet
Journal of Vision September 2021, Vol.21, 2324. doi:
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      Miao Li, Bert Reynvoet, Bilge Sayim; More crowded, less numerous: Crowding reduces the number of perceived items in numerosity perception. Journal of Vision 2021;21(9):2324.

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      © ARVO (1962-2015); The Authors (2016-present)

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Crowding refers to the deleterious effect of flankers on target perception. Recently, it has been proposed that crowding may have an impact on non-symbolic number processing. To investigate the role of crowding in numerosity perception, we used the radial-tangential anisotropy of crowding: radially placed flankers interfere more strongly with target perception than tangentially placed flankers. Stimuli consisted of different numbers of black discs presented on a gray background. We generated displays with different crowding levels (‘crowding’ and ‘no-crowding’ displays) while keeping other physical properties of the displays (e.g., inter-item spacing, occupancy area, convex hull, and density) as similar as possible. Displays consisted of a group of ‘base’ and ‘extra’ discs. ‘Crowding’ displays were generated by adding an extra disc inside the radially elongated elliptical crowding region of the base disc. ‘No-crowding’ displays were generated by rotating the elliptical crowding region (90 degrees) and adding an extra disc inside the (now tangentially elongated) ellipse around the base disc. In each trial, a reference display and a probe display appeared sequentially on the screen. Each ‘crowding’ and ‘no-crowding’ reference display was paired with ‘crowding’ as well as ‘no-crowding’ probe displays. The reference displays contained 40 discs, and probe displays contained 34, 36, 38, 40, 42, 44, or 46 discs. Participants were required to indicate the display that appeared to be more numerous. We found that subjective equality between crowding and no-crowding displays was shifted towards smaller numerosities in no-crowding displays, indicating that crowding displays were perceived as less numerous than no-crowding displays. The relative underestimation in the ‘crowding’ compared to the ‘no-crowding’ condition showed that radial compared to tangential arrangements reduced the number of perceived discs. Our results suggest that numerosity perception is subject to a radial-tangential asymmetry that may be driven by crowding.


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