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Detecting distortions of peripherally-presented letter stimuli under crowded conditions

View ORCID ProfileThomas S. A. Wallis, Saskia Tobias, Matthias Bethge, Felix A. Wichmann
doi: https://doi.org/10.1101/048272
Thomas S. A. Wallis
1Neural Information Processing Group, Faculty of Science, Eberhard Karls Universität Tübingen, Werner Reichardt Center for Integrative Neuroscience, Eberhard Karls Universität Tübingen & the Bernstein Center for Computational Neuroscience, Tübingen
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  • ORCID record for Thomas S. A. Wallis
Saskia Tobias
2Neural Information Processing Group, Faculty of Science, Eberhard Karls Universität Tübingen
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Matthias Bethge
3Werner Reichardt Center for Integrative Neuroscience, Eberhard Karls Universität Tübingen, Bernstein Center for Computational Neuroscience, Tübingen, Institute for Theoretical Physics, Eberhard Karls Universität Tübingen & the Max Planck Institute for Biological Cybernetics, Tübingen
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Felix A. Wichmann
4Neural Information Processing Group, Faculty of Science, Eberhard Karls Universität Tübingen, Bernstein Center for Computational Neuroscience, Tübingen & the Max Planck Institute for Intelligent Systems, Empirical Inference Department, Tübingen
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Abstract

When visual features in the periphery are close together they become difficult to recognise: 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 un-flanked 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.

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Posted October 05, 2016.
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Detecting distortions of peripherally-presented letter stimuli under crowded conditions
Thomas S. A. Wallis, Saskia Tobias, Matthias Bethge, Felix A. Wichmann
bioRxiv 048272; doi: https://doi.org/10.1101/048272
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Detecting distortions of peripherally-presented letter stimuli under crowded conditions
Thomas S. A. Wallis, Saskia Tobias, Matthias Bethge, Felix A. Wichmann
bioRxiv 048272; doi: https://doi.org/10.1101/048272

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