The Dimensionality of Color Vision in Carriers of Anomalous Trichromacy

Russ Hobbie and I discuss color vision in Chapter 14 of Intermediate Physics for Medicine and Biology.

14.15 Color Vision

The eye can detect color because there are three types of cones in the retina, each of which responds to a different wavelength of light (trichromate vision): red, green, and blue, the primary colors...

From Photon to Neuron:
Light, Imaging, Vision,
by Philip Nelson.

Imagine my shock when I read about possible tetrachromate vision in Philip Nelson’s book From Photon to Neuron. I downloaded the article Phil cited—“The Dimensionality of Color Vision in Carriers of Anomalous Trichromacy,” by Gabriele Jordan, Samir Deeb, Jenny Bosten, and John Mollon, Journal of Vision, Volume 10, doi:10.1167/10.8.12, 2010—and quote the abstract below.

Some 12% of women are carriers of the mild, X-linked forms of color vision deficiencies called “anomalous trichromacy.” Owing to random X chromosome inactivation, their retinae must contain four classes of cone rather than the normal three; and it has previously been speculated that these female carriers might be tetrachromatic, capable of discriminating spectral stimuli that are indistinguishable to the normal trichromat. However, the existing evidence is sparse and inconclusive. Here, we address the question using (a) a forced-choice version of the Rayleigh test, (b) a test using multidimensional scaling to reveal directly the dimensionality of the participants' color space, and (c) molecular genetic analyses to estimate the X-linked cone peak sensitivities of a selected sample of strong candidates for tetrachromacy. Our results suggest that most carriers of color anomaly do not exhibit four-dimensional color vision, and so we believe that anomalous trichromacy is unlikely to be maintained by an advantage to the carriers in discriminating colors. However, 1 of 24 obligate carriers of deuteranomaly exhibited tetrachromatic behavior on all our tests; this participant has three well-separated cone photopigments in the long-wave spectral region in addition to her short-wave cone. We assess the likelihood that behavioral tetrachromacy exists in the human population.

Flatland: A Romance of Many Dimensions,
by Edwin A. Abbott. If you haven’t
read Flatland, ask Santa for a copy
this Christmas (or click on this link).

Wow! IPMB claims that “other animals...[can] have more than three types [of cones]” but offers no hint that people can. How cool is that? This is like finding someone who lives in a four-dimensional world. Would a tetrachromat explaining color to me (a trichromat) be like Square in Flatland describing a sphere to the Triangles? (Square was thrown in prison for that!) What would life be like with four color receptors (red, green, blue, and orange) instead of three? Would you perceive a fundamentally different world, or would any difference be subtle? Could we use CRISPR or some other gene editing tool to expand our color vision? (I’ll take a dozen different cones, please.) Is it fair that only women can be tetrachromats? (No, but let’s not go there.) Is tetrachromacy a superpower?

San Diego woman Concetta Antico diagnosed with “super vision.”

I don’t know how accurate this news story is, but it’s interesting.

https://www.youtube.com/watch?v=QjocalycuiQ