May 2004
Volume 45, Issue 13
ARVO Annual Meeting Abstract  |   May 2004
What Determines Chromatic Discrimination?
Author Affiliations & Notes
  • V.C. Smith
    Ophthal & Vis Sci, University of Chicago, Chicago, IL
  • A. Zele
    Optom & Vis Sci, University of Melbourne, Melbourne, Australia
  • J. Pokorny
    Ophthal & Vis Sci, University of Chicago, Chicago, IL
  • Footnotes
    Commercial Relationships  V.C. Smith, None; A. Zele, None; J. Pokorny, None.
  • Footnotes
    Support  NIH Grant EY00901
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 2314. doi:
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      V.C. Smith, A. Zele, J. Pokorny; What Determines Chromatic Discrimination? . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2314.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract: : Purpose: Chromatic contrast discrimination for steadily viewed lights is determined by the chromaticity of a surround or of border elements adjacent to the test field. The data are consistent with adaptation to the surround or border, not adaptation to the test field. The current study investigated the proximity of the test field to the surround. Methods: Chromatic discrimination was assessed by four–alternative spatial forced choice. A 4.0° square stimulus appeared within a 10° x 12° rectangular surround. The test was a 1° square presented in an inner or outer quadrant of the stimulus. Test stimuli were presented as one cycle of a 1.5 sec raised cosine envelope. On each trial the test appeared as a small chromaticity difference in one quadrant and the observer identified the quadrant and the direction of chromatic change. The stimulus was presented as a Pulsed–Pedestal replacing the surround or as a Steady–Pedestal within the equiluminant surround. The stimulus varied in L–cone chromaticity at equal luminance (115 effective td). The surround was either metameric to the equal energy spectrum, or of higher (l = 0.76) or lower (l = 0.62) L–cone chromaticity on a constant S–cone line. Results: Inner quadrant tests: for the Pulsed–Pedestal paradigm, discrimination was best at the surround chromaticity, comparable to previous data. For the Steady–Pedestal paradigm, discrimination functions were flatter and less dependent on test or surround chromaticity. These functions indicated almost complete adaptation to the stimulus and resulted in near–optimal discrimination at all test chromaticities. Outer quadrant tests: data for both the Pulsed– and Steady–Pedestal were like the Pulsed–Pedestal data for inner quadrant tests, with the minimum at the surround chromaticity. Conclusions:Local spatial chromatic structure is an important determinant of chromatic discrimination for steadily viewed lights. Discrimination is best when a test is entirely embedded in a surround of the same chromaticity. Borders or surrounds dominate and degrade chromatic discrimination. However borders provide a sustained chromatic contrast signal and prevent fading of steadily viewed images.

Keywords: color vision • discrimination 

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