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Horse colour vision put to test in Caspian ponies

July 11, 2007

Researchers in Iran have put equine colour vision to the test and found that ponies can indeed see colour, and can discriminate between colours and grey.

In the paper "Color discrimination in the Caspian Pony", the researchers said that "although an early and influential review led to the often-cited conclusion that colour vision is rare among mammals, more recent findings suggest that it is actually widespread. According to Jacobs (1981, 1983), all non-nocturnal mammalian species that have been adequately examined show some color vision capacity, although the degree varies enormously. Data on the presence and characteristics of color vision in the horse, however, remain sparse (and almost none in the case of ponies)."

To test their theory, the team used eight Caspian ponies in the study, four mares and four stallions. The eight ponies were presented with a series of two-choice colour vs. grey discrimination problems.

Experiments were performed in a box of 3x3 metres containing a wall with two translucent panels that were illuminated from behind by light projected through colour or grey filters to provide the discriminative stimuli. Ponies were first adopted to the stall (box) with two panels in it and then learned to push one of the panels in order to receive the food rewards behind the positive stimuli in an achromatic light-dark discrimination task, and were then tested on their ability to discriminate between grey and four individual colors: red (617 nm.), yellow (581 nm.), green (538 nm.) and blue (470 nm.).

The criterion for learning was set at 85% correct response, and final testing for all colour vs. grey discrimination involved grey of varying intensities, making brightness an irrelevant cue. All ponies were tested with all four colours vs. grey discriminations. All the ponies, except Shahin and Vahid, successfully reached the criterion for learning blue colour vs. grey discrimination.

Only Hormoz and Vahid reached the criterion for learning green colour vs. grey discrimination. Except Shahin and Nasir none of the ponies reached the criterion for discriminating red and yellow vs. grey.

"So the answer to the question 'do the ponies see colour?' is yes, they can discriminate between the four selected colors vs. grey," the researchers said.



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