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Contrast independence of cardinal preference: stable oblique effect in orientation maps of ferret visual cortex

Authors

  • Agnieszka Grabska-Barwińska,

    1. Cognitive Neurobiology, Ruhr-University Bochum, 44780 Bochum, Germany
    2. International Graduate School of Neuroscience, Ruhr-University Bochum, Bochum, Germany
    3. Bernstein Group for Computational Neuroscience, Ruhr-University Bochum, Bochum, Germany
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  • Claudia Distler,

    1. Department of General Zoology and Neurobiology, Ruhr-University Bochum, Bochum, Germany
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  • Klaus-Peter Hoffmann,

    1. Department of General Zoology and Neurobiology, Ruhr-University Bochum, Bochum, Germany
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  • Dirk Jancke

    1. Cognitive Neurobiology, Ruhr-University Bochum, 44780 Bochum, Germany
    2. International Graduate School of Neuroscience, Ruhr-University Bochum, Bochum, Germany
    3. Bernstein Group for Computational Neuroscience, Ruhr-University Bochum, Bochum, Germany
    4. Department of General Zoology and Neurobiology, Ruhr-University Bochum, Bochum, Germany
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Dr D. Jancke, 1Cognitive Neurobiology, as above.
E-mail: jancke@neurobiologie.ruhr-uni-bochum.de

Abstract

The oblique effect was first described as enhanced detection and discrimination of cardinal orientations compared with oblique orientations. Such biases in visual processing are believed to originate from a functional adaptation to environmental statistics dominated by cardinal contours. At the neuronal level, the oblique orientation effect corresponds to the numerical overrepresentation and narrower tuning bandwidths of cortical neurons representing the cardinal axes. The anisotropic distribution of orientation preferences over large cortical regions was revealed with optical imaging, providing further evidence for the cortical oblique effect in several mammalian species. Our present study explores whether the dominant representation of cardinal contours persists at different stimulus contrasts. Performing intrinsic optical imaging in the ferret visual cortex and presenting drifting gratings at various orientations and contrasts (100%, 30% and 10%), we found that the overrepresentation of vertical and horizontal contours was invariant across stimulus contrasts. In addition, the responses to cardinal orientations were also more robust and evoked larger modulation depths than responses to oblique orientations. We conclude that orientation maps remain constant across the full range of contrast levels down to detection thresholds. Thus, a stable layout of the functional architecture dedicated to processing oriented edges seems to reflect a fundamental coding strategy of the early visual cortex.

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