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Color vision in horses (Equus caballus): deficiencies identified using a pseudoisochromatic plate test
Evelyn B Hanggi1, Jerry F Ingersoll, Terrace L Waggoner
1Equine Research Foundation, Aptos, CA 95001, USA. EquiResF@aol.com
Journal of Comparative Psychology (Washington, D.C. : 1983)
|February 28, 2007
Summary
Horses possess dichromatic color vision, similar to humans with red-green color deficiencies. This study utilized a novel pseudoisochromatic plate test to determine equine visual capabilities.
Area of Science:
- Comparative vision
- Animal behavior
- Ophthalmology
Background:
- Previous studies on equine color vision yielded inconsistent results.
- Existing methods like painted cards or electroretinogram flicker photometry lacked definitive conclusions.
Purpose of the Study:
- To investigate equine color vision using a pseudoisochromatic plate test for the first time in a nonhuman animal.
- To determine if horses exhibit dichromacy or other color vision deficiencies.
Main Methods:
- A pseudoisochromatic plate test, adapted from human color vision testing, was employed.
- Four horses (Equus caballus) performed a 2-choice discrimination task with various colored stimuli.
- Stimuli included gray, demonstration, protan-deutan, and tritan plates.
Main Results:
- Horses successfully discriminated gray and demonstration circles.
- No horses could differentiate protan-deutan plates or individual protan/deutan plates.
- All horses discriminated the tritan plate.
Conclusions:
- The results indicate horses are dichromats.
- Equine color vision appears analogous to human red-green color deficiencies (deuteranopia and protanopia).
- This study provides a definitive answer on equine color vision capabilities.
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