Equine color perception revisited

Cone excitation ratios correlate with color discrimination performance in the horse (Equus caballus).

“…Performance with C7 (blue-green) was less consistent, and more training was required (before the criterion was reached) than for any of the other colors. The study by Pick et al (1994) resulted in the single subject failing to reach the same criterion (of 10 consecutive correct choices) when discriminating green from gray. Despite the use of an alternative criterion of 70% correct responses, Macuda and Timney (1999) also concluded that chromatic discrimination was inconsistent with green and yellow.…”

“…Grzimek (1952) found that horses could discriminate yellow best, followed by green and then blue, but had some difficulty with red. Horses tested by Pick et al (1994) could reliably discriminate blue and red, but not green, from gray. Similar results were obtained by Macuda and Timney (1999), whose horses could discriminate red and blue, but not green or yellow, from gray (although, with the green stimulus used in their study, they noted that there was evidence that at least some of the chromatic information was available).…”

“…Successful discrimination of greens was demonstrated when the stimuli were presented at ground level both in horses (Grzimek, 1952) and deer (Birgersson et al, 2001) but not when they were presented to horses at nose height (Macuda & Timney, 1999;Pick et al, 1994). Smith and Goldman (1999) presented their stimuli at a height of 1.22 m from the ground and found individual differences in the performance of the horses.…”

“…Research into horses' ability to see colors has resulted in conflicting findings, both in studies adopting a behavioral approach (Grzimek, 1952;Macuda & Timney, 1999;Pick, Lovell, Brown, & Dail, 1994;Smith & Goldman, 1999) and in those investigating the spectral sensitivity of the cone photopigments of the equine retina (Carroll, Murphy, Neitz, Ver Hoeve, & Neitz, 2001;Macuda, 2000;Ver Hoeve, Neitz, & Murphy, 1999;Yokoyama & Radlwimmer, 1999). There is evidence that the horse, like other ungulates, possesses two types of cone photopigment, one maximally sensitive to short wavelengths, the other maximally sensitive to medium-long wavelengths.…”

The impact of visual perception on equine learning

“…Four colours (red, green, blue and yellow) had previously been used to test the ability of the horse to discriminate colours using this method. As noted by Murphy and Arkins (2007), there had been conflicting reports of which of these colours horses could successfully discriminate from greys (Grzimek, 1952;Pick et al, 1994;Macuda and Timney, 1999;Smith and Goldman, 1999). However, there was a general consensus that they possess two types of cone photopigment and are thus classed as dichromatic.…”