Equine Color Vision Research: Seeing Things Differently

If you have a horse of a different color, chances are your horse knows it--although he might not be able to say if he's red or green.

New physiological and behavioral research by various teams across the globe has added weight to the hypothesis that horses can see a wide range of colors, but they don't see them the same way humans do.

"Virtually all the data agree, first, horses do have the ability to see colors, and second, in suggesting that they have only two kinds of ... cones, as opposed to the three that humans have," said Canadian Brian Timney, PhD, professor of psychology and neuroscience at The University of Western Ontario and co-author of a recent review on vision and hearing research in horses. "This means they would confuse more colors than a human with normal vision would."

Image as seen by a human with normal color vision
Image as seen with equine color vision

Top: An outdoor scene as viewed by a human with normal color vision. Bottom: A digitally altered version of the picture that simulates the dichromatic color vision of the horse.

New Zealand PhD candidate in psychology Tania Blackmore of the University of Waikato co-authored the latest equine color perception research. Her findings, which will appear in an upcoming issue of Behavioral Processes, support an evolving international theory that horses see colors much like a human with red/green deficiency would.

Focusing on specific wavelength measurements, Blackmore's research showed horses can discriminate yellow from blue, contrary to older research, but that "green wavelengths may be more difficult for horses to see," she said.

Wavelength studies help resolve the "brightness problem" in color research--the risk that subjects might be perceiving brightness variations instead of color differences during tests, Timney said. Wavelength studies also test the fineness of their color vision.

A 2006 study led by British researcher Carol Hall, PhD, senior lecturer and program leader in equine sports science at Nottingham Trent University, showed a direct link between activity in horses' cones and their discrimination of colors presented to them. The horses in her study were consistently able to distinguish any color from gray, as she suspected they would.

"I had a horse that would ignore white lines on the road but had a real 'spook' if she came across yellow ones," Hall said. "Hence when I read that one study ... (which) concluded that they couldn't tell the difference between yellow and white, I felt strongly that this was not the case."

American researcher Joseph Carroll, PhD, assistant professor in ophthalmology at the Medical College of Wisconsin, led a physiological study of the equine eye in 2001 that confirmed the presence of two distinct cone types, classifying horses as dichromatic, as opposed to being trichromatic, like humans. Carroll's research provides an "anatomical base" for the behavioral research and allows equine professionals to work constructively with their dichromatic partners, he said.

"One could imagine designing easier-to-see jumps, for example," he said.

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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