Abstract
Neurobiological and molecular studies suggest a dichromatic colour vision in canine species, which appears to be similar to that of human red–green colour blindness. Here, we show that dogs exhibit a behavioural response similar to that of red–green blind human subjects when tested with a modified version of a test commonly used for the diagnosis of human deuteranopia (i.e. the Ishihara's test). Besides contributing to increasing the knowledge about the perceptual ability of dogs, the present work describes for the first time, to our knowledge, a method that can be used to assess colour vision in the animal kingdom.
Highlights
Dogs’ retinal structure clearly provides the potential for colour vision [1,2]
Dunn’s post hoc test revealed that this main effect was owing to the score for alerting behavioural response to the behavioural response towards the control cat animation (B-Cat) stimulus being higher with respect to other stimuli: B-Cat (3.75 ± 0.16 (s); m ± s.e.m.) versus G-Background-1 (0.44 ± 0.17 (s); m ± s.e.m.) (p < 0.01); B-Cat versus G-Background-2 (0.66 ± 0.11 (s); m ± s.e.m.), A-Cat-2 (0.62 ± 0.18 (s); m ± s.e.m.) and A-Cat-6 (0.75 ± 0.25 (s); m ± s.e.m.) (p < 0.05)
Our results revealed that during presentations of a cat’s moving animations having the same red– green colour shade of the number ‘2’ of Ishihara’s plate no. 22 (i.e. RG-Cat-2), most of the dogs exhibit an orienting response to the stimulus together with clear targeting behaviour
Summary
Visual-evoked potential [3,4] and immunohistochemical [1] studies have demonstrated that dogs possess two classes of cone pigments, one sensitive to long/medium wavelength light (555 nm spectral sensitivity; red/green) and the other sensitive to short wavelength light (429 nm spectral sensitivity; blue) The presence of these two discrete cone subtypes indicates a potential dichromatic vision. Concerning visual acuity, dogs are less able than humans to perceive clearly all the details of an object (four to eight time worse than humans) [5,6] This is owing to the different neural structures of the dogs’ eyes and in particular to the fewer connections of the rods to the ganglion cells and the smaller number of optic nerve fibres [5]. Employed technique of testing colour vision in dogs uses associative learning with a food 2 reward [9,10,11]. Considering that dogs’ vision is weaker than the human one, this could affect their responses in an ethological experiment [6], deepening the understanding of colour perception could be decisive in the design of visual tasks suitable for dogs’ visual capabilities
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