September 2005
Volume 5, Issue 8
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2005
Sensitivity to color and luminance transformations in real versus phase-scrambled natural scenes
Author Affiliations
  • Ali Yoonessi
    McGill Vision Research, Department of Ophthalmology, McGill University, Montreal H3A 1A1, Canada
  • Frederick A. A. Kingdom
    McGill Vision Research, Department of Ophthalmology, McGill University, Montreal H3A 1A1, Canada
Journal of Vision September 2005, Vol.5, 277. doi:10.1167/5.8.277
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      Ali Yoonessi, Frederick A. A. Kingdom; Sensitivity to color and luminance transformations in real versus phase-scrambled natural scenes. Journal of Vision 2005;5(8):277. doi: 10.1167/5.8.277.

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Abstract

Aim

Traditionally, thresholds for discriminating colour and luminance differences have been measured using stimuli such as disks, gratings or gabors, and accounted for in terms of the responses of relatively low-level mechanisms in the visual pathway. On this basis we would not expect the higher-order structure of, for example, natural scenes to be a factor determining colour and luminance discrimination thresholds. We therefore decided to compare discrimination thresholds between natural scenes and phase-scrambled versions of the same scenes.

Method

The stimuli were fifty calibrated color photographs of everyday scenes and fifty phase-scrambled images. The chromaticity and saturation of every pixel was represented as a vector in a modified version of the MacLeod-Boynton color space, and could be translated, rotated, compressed, or randomly repositioned within that color space. Thresholds for detection of each type of transformation were measured using a two-alternate forced choice method.

Results

Thresholds for all types of transformations in color space were significantly lower in natural scenes compared to phase-scrambled images. Thresholds for detecting random changes in color, in the form of either Gaussian or fractal noise, were considerably lower in natural compared to phase-scrambled images.

Conclusion

The structure of natural scenes plays a significant role in our ability to discriminate colour and luminance differences.

Yoonessi, A. Kingdom, F. A. A. (2005). Sensitivity to color and luminance transformations in real versus phase-scrambled natural scenes [Abstract]. Journal of Vision, 5(8):277, 277a, http://journalofvision.org/5/8/277/, doi:10.1167/5.8.277. [CrossRef]
Footnotes
 Supported by Canada Institute of Health Research grant #MOP-11554 given to F.K.
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