Volume 8, Number 1, Article 2, Pages 1-19 doi:10.1167/8.1.2 http://journalofvision.org/8/1/2/ ISSN 1534-7362
Chromatic discrimination of natural objects
Thorsten Hansen
Department of Psychology, Justus-Liebig-University, Giessen, Germany
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Martin Giesel
Department of Psychology, Justus-Liebig-University, Giessen, Germany
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Karl R. Gegenfurtner
Department of Psychology, Justus-Liebig-University, Giessen, Germany
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Abstract

Studies of chromatic discrimination are typically based on homogeneously colored patches. Surfaces of natural objects, however, cannot be characterized by a single color. Instead, they have a chromatic texture, that is, a distribution of different chromaticities. Here we study chromatic discrimination for natural images and synthetic stimuli with a distribution of different chromaticities under various states of adaptation. Discrimination was measured at the adaptation point, where the mean chromaticity of the test stimuli was the same as the chromaticity of the adapting background, and away from the adaptation point. At the adaptation point, discrimination for natural objects resulted in threshold contours that were selectively elongated in a direction of color space matching the chromatic variation of the colors within the natural object. Similar effects occurred for synthetic stimuli. Away from the adaptation point, discrimination thresholds increased and threshold ellipses were elongated along the contrast axis connecting adapting color and test color. Away from the adaptation point, no significant differences between the different stimulus classes were found. The effect of the chromatic texture on discrimination seemed to be masked by the overall increase in discrimination thresholds. Our results show that discrimination of chromatic textures, either synthetic or natural, differs from that of simple uniform patches when the chromatic variation is centered at the adaptation point.

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History
Received January 19, 2007; published January 4, 2008
Citation
Hansen, T., Giesel, M., & Gegenfurtner, K. R. (2008). Chromatic discrimination of natural objects. Journal of Vision, 8(1):2, 1-19, http://journalofvision.org/8/1/2/, doi:10.1167/8.1.2.
Keywords
chromatic discrimination, natural objects, chromatic textures, chromatic distribution, spatial frequency
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