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  Discussion on Research Summary: Horses Color Vision in Dim Light
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DrO

Posted on Friday, Nov 14, 2008 - 9:07 am:

A great study that continues to define the limits of a horse's vision. As you are aware once the light begins to fail colors start to turn greyish. It would appear that horses are similar to humans in their ability to distinguish color as the light fails just being able to see color in moonlight. I presume they mean the light of a full moon as this is about what it takes for me to distinguish some colors. I continue to wait to see exactly how dark has it got to get for horses to not be able to see well enough to walk in a forest. I have let the horse bring me home in conditions where I could not see my hand in front of my face.
DrO

PLoS ONE. 2008;3(11):e3711.
The absolute threshold of colour vision in the horse.

Roth LS, Balkenius A, Kelber A.

Department of Cell and Organism Biology, Vision Group, Lund University, Lund, Sweden. lina.roth@cob.lu.se

Arrhythmic mammals are active both during day and night if they are allowed. The arrhythmic horses are in possession of one of the largest terrestrial animal eyes and the purpose of this study is to reveal whether their eye is sensitive enough to see colours at night. During the day horses are known to have dichromatic colour vision. To disclose whether they can discriminate colours in dim light a behavioural dual choice experiment was performed. We started the training and testing at daylight intensities and the horses continued to choose correctly at a high frequency down to light intensities corresponding to moonlight. One Shetland pony mare, was able to discriminate colours at 0.08 cd/m(2), while a half blood gelding, still discriminated colours at 0.02 cd/m(2). For comparison, the colour vision limit for several human subjects tested in the very same experiment was also 0.02 cd/m(2). Hence, the threshold of colour vision for the horse that performed best was similar to that of the humans. The behavioural results are in line with calculations of the sensitivity of cone vision where the horse eye and human eye again are similar. The advantage of the large eye of the horse lies not in colour vision at night, but probably instead in achromatic tasks where presumably signal summation enhances sensitivity.
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