Emergence of crowding: the role of contrast and orientation salience

Robert J. Lee, Josephine Reuther, Ramakrishna Chakravarthi, Jasna Martinovic* (Corresponding Author)

*Corresponding author for this work

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Crowding causes difficulties in judging attributes of an object surrounded by other objects. We investigated crowding for stimuli that isolated either S-cone or luminance mechanisms or combined them. By targeting different retinogeniculate mechanisms with contrast-matched stimuli, we aim to determine the earliest site at which crowding emerges. Discrimination was measured in an orientation judgement task where Gabor targets were presented parafoveally among flankers. In the first experiment, we assessed flanked and unflanked orientation discrimination thresholds for pure S-cone and achromatic stimuli and their combinations. In the second experiment, to capture individual differences, we measured unflanked detection and orientation sensitivity, along with performance under flanker-interference for stimuli containing luminance only or combined with Scone contrast. We confirmed that orientation sensitivity was lower for unflanked S-cone stimuli. When flanked, the pattern of results for S-cone stimuli was the same as for achromatic stimuli with comparable (i.e., low) contrast levels. We also found that flanker interference exhibited a genuine signature of crowding only when orientation discrimination threshold was reliably surpassed.
Crowding, therefore, emerges at a stage that operates on signals representing task-relevant featural (here, orientation) information. Since luminance and S-cone mechanisms have very different spatial tuning properties, it is most parsimonious to conclude that crowding takes place at a neural processing stage after they have been combined.
Original languageEnglish
Article number20
Pages (from-to)1-21
Number of pages21
JournalJournal of Vision
Issue number11
Early online date28 Oct 2021
Publication statusPublished - Oct 2021

Bibliographical note

JM, RC and JR were supported by grants BB/R009287/1 and BB/S020640/1 from the BBSRC. RJL was supported by an early career research visit grant from the School of Psychology, University of Aberdeen. The authors would like to thank Daniel Coates for constructive feedback and Gabi Lipan for creating the image of the DKL space for Figure 1.

Data Availability Statement

Data is deposited on OSF - https://osf.io/5a8ec/.


  • colour
  • luminance
  • crowding
  • orientation discrimination
  • contrast
  • S-cones
  • Sensory Systems
  • Ophthalmology


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