THROUGH A HORSES EYE
By Walter Berger © 2001
There has long been controversy regarding what the horse can see and what it can not. Until fairly recent years not much research has been devoted to the subject, possibly due to the difficulty of working with the horse as a subject.
In 1993 and 1994 several large scientific research projects were carried out in order to rectify this lack of knowledge. I will only try to explain some of the findings regarding colour and light perception in this article. You will have to wait for the next instalment for the bit on overall vision and depth perception.
The back of the retina contains several types of light receptors, rods and cones. Rods are more sensitive to lower light conditions and their fairly high numbers give the horse good night vision. It has been said that a lot of Appaloosa’s are or can be night blind, but I have yet to see proof of this. This could be due to lack of rods.
In the past there has been arguments for and against the horse's ability to perceive colours. The fact is that the horse is able to perceive some colours in a limited way. Cones are a more specialised light receptor. Cones can be sensitive to specific frequencies of light as opposed to all light. Therefor in order to have colour vision all you need is cones receptive to the different colours. Humans have cones receptive to blue, green and red. Yellow light is a mixture of red and green.
As it turns out horses only have receptors sensitive to blue and red light. Therefore they are green colour blind, and your lush green paddock would look something like a drab shade of grey to them. Lighter shades of blue, red, orange or yellow would also appear as shades of grey. So the biggest contrast you could get, apart from black and white, would be blue and red.
This was discovered by getting horses to push square panels of different colours for rewards. The panels were designed to reflect the same amount of light, even though they appear as different colours to us. It took 200 tries for a horse to reliably push the red panel over a grey panel. It took 430 tries for the horse to select a blue panel over a grey panel. Even after 1400 tries (researchers are patient, aren’t they) a horse could not reliably pick green over grey.
So the next time your horse stumbles over that rock in the track, or stops at a show jump, think about it. Is it the horses lack of attention, obstinacy or an inability to properly see the object that is causing the problem.
Source: The Nature of Horses, Stephen Budianski TOP