Abstract
Humans have selectively bred and used dogs over a period of thousands of years, and more recently the dog has become an important model animal for studies in ethology, cognition and genetics. These broad interests warrant careful descriptions of the senses of dogs. Still there is little known about dog vision, especially what dogs can discriminate in different light conditions. We trained and tested whippets, pugs, and a Shetland sheepdog in a two-choice discrimination set-up and show that dogs can discriminate patterns with spatial frequencies between 5.5 and 19.5 cycle per degree (cpd) in the bright light condition (43 cd m-2). This is a higher spatial resolution than has been previously reported although the individual variation in our tests was large. Humans tested in the same set-up reached acuities corresponding to earlier studies, ranging between 32.1 and 44.2 cpd. In the dim light condition (0.0087 cd m-2) the acuity of dogs ranged between 1.8 and 3.5 cpd while in humans, between 5.9 and 9.9 cpd. Thus, humans make visual discrimination of objects from roughly a threefold distance compared to dogs in both bright and dim light.
Highlights
World-wide, around 400 pure dog breeds are recognised, all descended from wolves [1,2,3,4], and selectively bred by humans for different phenotypic traits or behaviours over many thousands of years
Our study revealed a higher visual acuity in dogs in bright light conditions than what would be expected from earlier studies
While the visual acuity of on Shetland sheepdog and two of the whippets matched the results from earlier behavioural studies on dogs (5.5–6.2 cpd) [15], the acuity of the other two whippets and the pug was two to four times higher (Fig 3 and Table 1)
Summary
World-wide, around 400 pure dog breeds are recognised, all descended from wolves [1,2,3,4], and selectively bred by humans for different phenotypic traits or behaviours over many thousands of years. It is not clear how this domestication has affected the senses of dogs, but it may be assumed that many human activities that dogs participate in, and have been selected for, have served to uphold a strict demand on sensory abilities.
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