How does a horse see color?

Have you ever wondered what a horse can see? Does he see the world in color, like you and me, or in black and white? I recently came across an article from the Journal of Vision that examined this very question. Researchers from the Medical College of Wisconsin and from the University of Wisconsin-Madison teamed up in 2001 to examine horse vision. You can view the whole article for free online here, although it’s a bit technical. I’ve pulled out some of the interesting photos, diagrams and bits of information from the article for this blog post.

Horses can see some colors. However, they don’t see color like humans do. Humans and other primates have what is called trichromatic color vision because they have three types of cone cells in their eyes. The most common form of color vision in non-primate mammals, including horses, is dichromatic color vision. Horses and other animals with this type of vision only have two types of cone cells in their eyes.

The diagram to the right shows the hues that normal humans can see and the hues that horses can see. Normal humans can see four basic color hues–red, green, blue, and yellow. They can also see lots of intermediate hues between each of these primary hues. A horse’s vision is similar to a person who is red-green color blind. Horses can only see blues and yellows. However, unlike a human, a horse can probably not see any intermediate hues.

The four photos below come from the journal article. The two top photos are “regular” photos, as a normal human would see the world. The two bottom photos have been doctored so that they approximate how a horse would likely see the world. In addition to altering the colors, the sharpness of the photos have also been doctored to match a horse’s vision.

Notice how some things that jump out in the top photos are difficult to see in the bottom photos. For example, in the top photo, the child on the right is wearing a very bright jacket. However, in the bottom photo, the horse sees the jacket as a shade of grey. Knowing how your horse sees the world is important for training and riding. Since horses see the world very differently than us, they will react differently than we might expect them to in certain situations.

(click on the image to view a larger version)

Diagram and photos are from:
Carroll, J., Murphy, C. J., Neitz, M., Ver Hoeve, J. N., Neitz, J. (2001). Photopigment basis for dichromatic color vision in the horse. Journal of Vision, 1, 80-87.

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