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Geisbauer, G., Griebel, U., Schmid, A., & Timney, B. (2004). Brightness discrimination and neutral point. Can. J. Zool, 82(4), 660–670.
Abstract: Abstract: Equine brightness discrimination ability and color discrimination were measured using a two-choice discrimination
task. Two Haflinger horses (Equus caballus L., 1758) were trained to discriminate 30 different shades of grey
varying from low to high relative brightness. Their ability to distinguish shades of grey was poor, with calculated
Weber fractions of 0.42 and 0.45. In addition, a “neutral point” test to determine the dimensionality of color vision
was carried out. Three hues of blue-green were tested versus a range of grey targets with brightnesses similar to those
of the blue-green targets. A neutral point was found at about 480 nm. Thus, we can conclude that horses possess
dichromatic color vision.
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