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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  • Lottie Erikson

    I'm halfway through a part time uni course on the horse's senses and behaviour, with a teacher who wrote her thesis on the colour vision of vertebrates. A funny detail is what she found when a group of hunters asked her for information about how moose see colours (which is the same way horses do): the orange ribbon the hunters wore around their hats would, for a moose or horse, be perceived as exactly the hue of a young fir branch.

    So those orange cones which are popular to use in training, for both horses and dogs, may not be the best choice when working on grass. The contrast is nowhere as sharp as we perceive it – just like shown in the photo above with the brightly coloured jacket. Reds and oranges are perceived as different shades of green by the horse.
    Haven't read the article so I don't know if this is mentioned there, but there is a certain wavelength (480 nm) where the horse's two types of cones are equally stimulated. What humans see at this wavelenght is a blue-green hue. When presented with that blue-green hue and a grey one with the same brightness, horses can't tell the difference between them. So they may perceive it as blue-green, or they may perceive it as grey; it's impossible to say.

    • Thanks for all the additional information, Lottie.

      I find that fascinating to think about the cones not being bright. I use little orange cones all the time in my training! I guess that yellow cones might be the better choice?

      ~Mary

      • Lottie Eriksson

        Well, yellow ones might be better, but I don't think you need to throw away your orange ones either! The horses do see them of course, they stlll have a shape and a brightness, though they may not stand out very clearly against certain backgrounds. There are three factors that determine how a colour is perceived: hue, brightness and saturation. So one particular hue (the same wavelength of light) can look very different depending on its brightness and saturation. 

        I think just being aware that horses' vision is different from ours can help us understand them better. Another piece of the puzzle when trying to figure out why they react the way they do.

  • Bonnie

    I find that very sad to live in a world where the bright green of grass can never be seen by a horse, or any other of the wonderful colors, like the colors of other horses… I wonder why nature did that?  

    • Lottie Eriksson

      Who knows, maybe the particular green shade of spring grass is extra beautiful in the eyes of a horse? And they also have senses that are better than ours: their night vision is better, their sense of smell is better, and they hear sounds of higher frequencies than we do.

      We humans miss out on lots of colours too. Most vertebrates have four types of cones: in addition to cones sensitive to blue, green and red, they also have a type that's sensitive to ultraviolet. So fish, birds and lizards see things we cannot percieve. There are species of birds, for instance, where the females find males with lots of ultraviolet in their plumage more attractive than those with less.

      The reason most mammals only have two types of cones is probably that the earliest mammals were active at night, when colour vision isn't of much use. So they lost one cone type. The additional cone type that lets us humans see red has developed later.

    •  With only 2 cones..horses see
      only blues & yellows. Most birds have 4 cones and can see colors invisible
      to us (ultra violet, infra red).
       it is mind boggling I mean can you just try to even imagine how much
      better (and clearer!)birds can see than us …when you look at the incredible
      difference 2 cones was from 3…4 cones must be amazing like being on
      “Pandora”!).

  •  With only 2 cones..horses see
    only blues & yellows. Most birds have 4 cones and can see colors invisible
    to us (ultra violet, infra red).
     it is mind boggling I mean can you just try to even imagine how much
    better (and clearer!)birds can see than us …when you look at the incredible
    difference 2 cones was from 3…4 cones must be amazing like being on
    “Pandora”!).

    • michelle

      the person who said this is exactly what i have been thinkink e.g. how sad it is for a horse to never see the green of grass and the other colours too, and sad for all the other animals that only have 2 cones
      . i am now wondering if things are not really coloured how they are but it is the cones in the eye that makes us see things in colour. does pink then really exsit in nature or is it that our eyes see pink