Attention, Perception, & Psychophysics

, Volume 79, Issue 3, pp 850–862 | Cite as

Detecting distortions of peripherally presented letter stimuli under crowded conditions

  • Thomas S. A. Wallis
  • Saskia Tobias
  • Matthias Bethge
  • Felix A. Wichmann


When visual features in the periphery are close together they become difficult to recognize: something is present but it is unclear what. This is called “crowding”. Here we investigated sensitivity to features in highly familiar shapes (letters) by applying spatial distortions. In Experiment 1, observers detected which of four peripherally presented (8 deg of retinal eccentricity) target letters was distorted (spatial 4AFC). The letters were presented either isolated or surrounded by four undistorted flanking letters, and distorted with one of two types of distortion at a range of distortion frequencies and amplitudes. The bandpass noise distortion (“BPN”) technique causes spatial distortions in Cartesian space, whereas radial frequency distortion (“RF”) causes shifts in polar coordinates. Detecting distortions in target letters was more difficult in the presence of flanking letters, consistent with the effect of crowding. The BPN distortion type showed evidence of tuning, with sensitivity to distortions peaking at approximately 6.5 c/deg for unflanked letters. The presence of flanking letters causes this peak to rise to approximately 8.5 c/deg. In contrast to the tuning observed for BPN distortions, RF distortion sensitivity increased as the radial frequency of distortion increased. In a series of follow-up experiments, we found that sensitivity to distortions is reduced when flanking letters were also distorted, that this held when observers were required to report which target letter was undistorted, and that this held when flanker distortions were always detectable. The perception of geometric distortions in letter stimuli is impaired by visual crowding.


2D shape and form Spatial vision Reading Distortion Metamorphopsia 



Designed the experiments: TSAW, ST, FAW, MB. Programmed the experiments: ST, TSAW. Collected the data: ST, TSAW. Analyzed the data: TSAW, ST. Wrote the paper: TSAW. Revised the paper: ST, FAW, MB. We thank Peter Bex and William Harrison for helpful comments on the manuscript.

Supplementary material

13414_2016_1245_MOESM1_ESM.pdf (944 kb)
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Copyright information

© The Psychonomic Society, Inc. 2017

Authors and Affiliations

  • Thomas S. A. Wallis
    • 1
    • 2
    • 3
  • Saskia Tobias
    • 1
  • Matthias Bethge
    • 2
    • 3
    • 4
    • 5
  • Felix A. Wichmann
    • 1
    • 3
    • 6
  1. 1.Neural Information Processing Group, Faculty of ScienceEberhard Karls Universität TübingenTübingenGermany
  2. 2.Werner Reichardt Center for Integrative NeuroscienceEberhard Karls Universität TübingenTübingenGermany
  3. 3.Bernstein Center for Computational NeuroscienceTübingenGermany
  4. 4.Institute for Theoretical PhysicsEberhard Karls Universität TübingenTübingenGermany
  5. 5.Max Planck Institute for Biological CyberneticsTübingenGermany
  6. 6.Empirical Inference DepartmentMax Planck Institute for Intelligent SystemsTübingenGermany

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