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Michael Jansen, Martin Giesel, Qasim Zaidi; Detecting animals in natural surroundings: The role of color distributions. Journal of Vision 2011;11(11):360. doi: 10.1167/11.11.360.
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© ARVO (1962-2015); The Authors (2016-present)
Coloration and pattern are thought to play roles in crypsis for evading predators, and display for attracting mates or warning enemies. Colors of animals and their natural surroundings form distributions elongated between spectral reflectances and illumination spectra. We investigate whether color distributions contribute to camouflage and display independent of spatial information.We obtained 30 images of animals distinctly visible on the natural surround, and 29 images of animals camouflaged against their background. Colors were extracted from each pixel in the animal's image, and each pixel in the surrounding annulus of roughly the same width as the animal. The surround colors were randomly placed in the pixels of an 8 deg square, and the animal colors randomly in a 1.5 × 6 deg rectangle. Random masks were made as averages of all the images. Duration thresholds for discrimination of each animal color distribution from its background distribution, were measured by presenting rectangles randomly as horizontal or vertical in the center of the square, followed by a mask, in a 2AFC method of constant stimuli for durations from 8.5 to 100 msec. Besides the original distributions, the experiment also used isoluminant and achromatic versions of the random displays. Thresholds were determined from psychometric curves fitted to each image for each condition and for each observer. Comparing isoluminant thresholds to thresholds for the original distributions, reveals whether an animal distribution can be reliably detected on the basis of chromatic information alone. Comparing achromatic thresholds to thresholds for the original distributions reveals whether the addition of chromatic information enhances detection of an animal distribution. In general, both tests separated the images into the same groups, animals that could be detected using chromatic signals, and animals that could not. We will show that the usefulness of chromatic signals is related to the angular difference between color distributions.
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