December 2022
Volume 22, Issue 14
Open Access
Vision Sciences Society Annual Meeting Abstract  |   December 2022
Numerosity modulates the gain of pupillary response
Author Affiliations & Notes
  • David Burr
    University of Florence
  • Elisa Castaldi
    University of Florence
  • Antonella Pomè
    University of Florence
  • Giudo Cicchini
    CNR Neuroscience Institute, Pisa
  • Paola Binda
    University of Pisa
  • Footnotes
    Acknowledgements  European Union (EU)" and "Horizon 2020 - ERC Advanced  Grant N. 832813 — GenPercept  and Italian Ministry of Research (MIUR) 
Journal of Vision December 2022, Vol.22, 3151. doi:
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      David Burr, Elisa Castaldi, Antonella Pomè, Giudo Cicchini, Paola Binda; Numerosity modulates the gain of pupillary response. Journal of Vision 2022;22(14):3151.

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

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The pupil responds primarily to prevailing luminance, but is also modulated by cognitive factors, such as perceived luminance and attention, even when physical luminance is matched. Here we asked whether perceived numerosity may also modulate the pupil light response. We recorded pupil size while adult participants viewed clouds of white or black dots displayed on a gray background. In all conditions, the total number of pixels forming the dots was always constant (20% of the screen), so the luminance of the black patterns was the same for all conditions, as was that of the white. We varied apparent numerosity in three ways: by changing the number of dots (18 or 24); by connecting pairs of dots with lines, reducing perceived numerosity by the “connectedness illusion”; or by adaptation to high or low numerosities. In all cases participants simply observed the stimuli without performing any task. As expected, participant pupils constricted to white patterns and dilated to dark patterns. Importantly, however, both constriction and dilation were stronger for patterns with higher perceived numerosity, either physical or illusory, so the strength of the pupillary luminance response scaled with perceived numerosity. Overall, this study shows that even without explicitly directing attention to numerosity via instructions or a task, perceived number spontaneously modulates the very basic pupillary reflex, suggesting that numerosity is a spontaneously encoded visual feature.


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