Color discrimination in Caspian pony

Abstract

Although an early and influential review led to the often-cited conclusion that color vision is rare among mammals, more recent findings suggest that it is actually widespread. According to Jacobs, 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 none in the case of ponies. Eight Caspian ponies were presented with a series of two-choice color vs. grey discrimination problems. One mare pony was eliminated due to traumatic injury to the eye. Experiments were performed in a box of 3 × 3 meter containing a wall with two translucent panels that were illuminated from behind by light projected through color 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. The ponies 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 color vs. grey discrimination involved grey of varying intensities, making brightness an irrelevant cue. The ponies were tested with all four colors vs. grey discriminations. Except two ponies, the rest were successfully reached the criterion for learning blue color vs. grey discrimination. Only two ponies reached the criterion for learning green color vs. grey discrimination. Only tow ponies reached the criterion for discriminating red and yellow vs. grey. So the answer to the question "do the ponies see color" is yes, they can discriminate between the four selected color vs. grey.