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Global contour shapes are coded differently from their local components.

Jason Bell1, Fredrick A A Kingdom

  • 1McGill Vision Research, Department of Ophthalmology, McGill University, 687 Pine Avenue West, H4-14, Montreal, Quebec, Canada H3A 1A1. jason.bell@mail.mcgill.ca

Vision Research
|April 21, 2009
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Summary
This summary is machine-generated.

Global contour shapes are processed differently than local components. The radial frequency amplitude after-effect (RFAAE) shows shape mechanisms are amplitude-selective but not for contrast polarity or spatial-frequency.

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Area of Science:

  • Visual perception
  • Computational neuroscience
  • Psychophysics

Background:

  • Mechanisms processing curved contours show selectivity for low-level attributes like luminance contrast polarity and spatial-frequency.
  • Mechanisms processing curvature-defined global shapes are not selective for these low-level attributes.
  • Methodological differences in previous studies may explain these varied findings.

Purpose of the Study:

  • To investigate if global contour shapes are represented differently from their local components.
  • To introduce and utilize the radial frequency amplitude after-effect (RFAAE) as a novel research tool.
  • To clarify the role of low-level attributes in the processing of global shape information.

Main Methods:

  • Demonstration of the radial frequency amplitude after-effect (RFAAE), an analog of the shape-amplitude after-effect (SAAE).
  • Utilizing an appearance-based task to assess the selectivity of radial frequency (RF) shape mechanisms.
  • Adaptation paradigms to investigate the bidirectionality and attribute selectivity of the RFAAE.

Main Results:

  • The RFAAE is bidirectional, indicating that RF-shape mechanisms are selective for amplitude.
  • The RFAAE is not selective for luminance contrast polarity.
  • The RFAAE is not selective for luminance spatial-frequency.

Conclusions:

  • Global contour shapes are processed differently from their local components.
  • Findings using an appearance-based approach align with previous performance-based studies.
  • Higher-level visual processing stages appear to be relatively agnostic to low-level visual attributes for global shape representation.