ON THE VISION OF DOGS

Following my Comment yesterday applying the geometric principles of this work to define the visual characteristics of cats, I have found a reference Topographical characterization of cone photoreceptors and the area centralis of the canine retina (Mowat et al) measuring the distribution of cone and rod receptors on the retina of canines that leads to similar predictions about the vision of this species.

Again, I will let the paper speak for itself (omitting the references):

“The dog has two discrete cone subtypes; the two cone opsins are sensitive to long/medium wavelength light (555 nm spectral sensitivity; red/green or L/M-opsin) and short wavelength light (429 nm spectral sensitivity; blue or S-opsin. Previous studies have examined cone density in retinal cross sections Unlike the detailed characterization of cone distribution in other species, cone subtype distribution in retinal flatmounts has only been examined qualitatively in dogs, and the location of the area centralis has not been accurately defined.”

There is much to be written here but I thought the conclusion to be sufficiently important to summarize in the following.

The authors present views of the cone and rod distribution in what they term the area centralis of the dog’s retina in their Figure 1. It is clear that receptor distribution in this region is similar to the cat retina with no evidence of the tight packing (hexagonally arrayed) of cones as characteristic of the human retina. This eliminates, in the context of this work, any long wavelength sensitive region (i.e., a “fovea”).

Therefore, and as stated in their remarks above, the vision of dogs will be dichromatic. This means (refer to the discussion in yesterdays Comment) that there can be no central geometrically- defined, “fulcrum” from whence the hues of “color” may be synthesized.

I propose that dogs, therefore do not see the hues of “color” in the same sense that humans do. What they do see is visual image of the world composed of two very discrete wavelengths that are defined by two geometric lengths. I cannot emphasize enough the narrow discrete character of this light detection process.

I would believe that dogs see an image synthesized in a band between these two discrete wavelengths but that image in my view must be some sort of grayscale image.

I would expect that experiments with dogs would find an ability to discern the difference between these two wavelengths but this does not mean that they see color.

I emphasize again the difference that has been muddled through history between the detection on the retina of: a.) discrete wavelengths (the three in the human are termed “primary”) an, b.) the subsequent synthesis of the hues that we term “color” – that follows from the presence of central geometrically-defined mid band fulcrum and color vision teaching of Edwin Land.

Now what will be confusing – using traditional (and incorrect) thought, the authors attribute detection of the two wavelengths to the existence of “two discrete cone subtypes” (from the above) and associated opsins etc. I assert that these are not different types (or traditionally, “classes”) of cones but different discrete geometric spacings. As I have proposed, the different opsins represent “structural cages” that hold the ubiquitous retinal molecules in the the differentially sized rod and cone receptors.

Respectfully submitted,

GCH

Ojai,CA

8.18.09