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Home » Dave’s DiegesesJuly 2005 » Dave’s Diegesis: Coloratura

Dave’s Diegesis: Coloratura

Clouds come floating into my life, no longer to carry rain or usher storm, but to add color to my sunset sky.
Rabindranath Tagore

Everyone’s talking about Brian Roberts and his vision-enhancing MaxSight contacts lenses developed by Nike and Bausch & Lomb. My old comrades in arms Bronson Arroyo and Mike Timlin wear them, as do Danny Graves, Ken Griffey, Jr., and Joe Mauer. The lenses for atheletes in action sports have amber-tinted lenses that filter blue light wavelengths and emphasize the viewer’s perception of red colors. Cutting out the blue light reduces visual noise so that moving objects, such as a pitched baseball, stand out in relation to the background. The lenses also have medical benefits for people with extended solar exposure. Timlin has pterygium, a thickening of corneal tissue that can lead to vision loss.

This scientific breakthrough got me thinking about our exceptional ocular abilities and how they are tied to genetics. Myself, I’m a trichromat like most people; my retinas have red, green, and blue cone photopigments enabling me to have the normal human perception of visible light.

Approximately 8% of men are prone to color-blindness because of the placement of the genes that express red (RCP) and green (GCP) cone photopigments are adjacent on the X chromosome. Since men only have a single X chromosome, they have only one chance to get the correct expression of RCP and GCP. If a female carries a mutated set of photopigments genes in a given egg, her male offspring will not perceive reds or greens as distinct colors because of lack of the proper photopigments. These men would be considered dichromats, and you’ve probably stifled a giggle if you’ve seen one try and dress himself.

In stark contrast, by this same genetic quirk it is possible for women to have the ability to receive four different wavelengths of light, making them tetrachromats. Since women have two X chromosomes, and the expression of GCP or RCP is not limited to a single wavelength value, on rare occasions women could inherit the potential ability to see slightly different values of these colors.

Tetrachromacy would require X-inactivation during embryonic development, where aspects of both the father’s and mother’s X chromosomes would be expressed in their daughter, resulting in a genetic mosaic. An example in cats you can readily see are calico patterned felines. This hypothetical tetrachromat could conceivably perceive the typical red, green, and blue, along with an additional slightly shifted red or blue wavelength.

This raises the fundamental question of whether or not our brain is built to receive four channels of color. Would the developing brain learn to process this additional wavelength, or are we hardwired to only see the three? How early would a developing human need to begin receiving this extra light frequency to be able to process it meaningfully? Would it lay dormant because a tetrachromat would be surrounded by trichromats that could not train her to notice the distinctions she may perceive?

I was asking these questions to my potential new colleagues Tom Caron and Sam Horn. Hopefully you caught me on the NESN pre-game tonight. It’s an exciting new endeavor for me, and I have to say I’ve already impressed my peers, including Michelle Damon who, as soon as she saw mentioned how much Johnny talked about me. We’re meeting sometime this weekend to discuss color perception in more detail. A new beginning, and already I get share the most valuable gift of all: knowledge.

Every Friday, Dave McCarty will join us to discuss a topic of interest to him and probably no one else but the author of this site and other lone science geeks with a literary bent.


Wow. Being a new reader of this blog, I did not expect to find a discussion of the genetics of vision, but it's an interesting topic. I would guess that a female with four different cone photoreceptor genes would be a tetrachromat (ignoring the issue of whether in most cases it's different enough to change perceptions). My reason for saying this is that brain development is quite dependent on what input it receives. I think an analogy with learning language may be valid--if when young someone's brain is exposed to four different types of color input, that brain will probably construct or modify its visual cortex accordingly.

This leads to the question of whether engineered versions of photoreceptors could be made that can see in the near UV or infrared. This plus gene therapy would open up a lot of possibilities for anyone interested in writing some science fiction.

I do believe in the plasticity and expansiveness of the human brain. We all learn to flip the images that we receive on our retinas so that they are correctly perceived by our visual cortex.

In the article linked in this post entitled "Looking for Madam Tetrachromat," they have comments from women whose behaviors corroborate the evidence that our brains would be able to process a fourth input. One of the researchers does mention that the frequency of the shifted green or red additional inputs would have to be sufficiently different from the existing green or red input in order to make any difference.

Language acquisition is a more recent development than processing visual signals, however. Could it be possible that the mammalian brain has done away with the ability to process wavelengths outside of the visible spectrum in order to accommodate other functions? I found this article that addresses some of the aspects of how mammalian evolution impacts color perception.

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