reperiendi

Try to see things my way…

Posted in Uncategorized by Mike Stay on 2005 April 9

The genes for red and green color vision are right next to each other on the X chromosome. The gene for blue is on a different chromosome. Sometimes, during meiosis, the genes don’t go to the right places. The possible combinations are (), (r), (rr), (g), (gg), (rg). If (rg) doesn’t occur, and the child is male, then he’ll be colorblind (or perhaps an anomalous trichromat). If (rr) or (gg) occurs, and the child is female, she’ll inherit (rg) from the other X and will have a good chance of becoming a tetrachromat. The peak sensitivity of the two needs to differ enough that the brain perceives them as separate colors.

William Stark had a lens removed from one eye at age 12, at which point he realized that he could see near-UV light in the 300-400 nm range. It turns out that the lens is opaque to that frequency of light. He went on to study UV perception in Drosophila and published the seminal paper on UV perception in humans. He perceives UV light as pale blue; his hypothesis is that all color receptors are somewhat sensitive in the UV range, but blue slightly moreso.

One researcher, however, believes that humans actually have four receptors, including one for UV, and that all humans could potentially be tetrachromats if not for the lens. If this is true, then akaphic humans might potentially perceive near-UV as a separate color if they learn to see with all four colors rather than getting a fourth color after the brain has learned to see with only three. What colors will the blind see when they get bionic eyes? What if the spectrum differs between eyes?

Synesthesia is a condition that affects the perception of color in humans. It’s well-known that the brain preprocesses sensory information far earlier than we become consciously aware of it. Synesthetics have distinct sensory perceptions associated with ideas. Often, these come in the form of color, but may be touch, smell, sound, or even spacial perception (“the number sixteen is to my right”). Ramachandran was the first to use pop-out tests to show that synesthesia was not just the result of an overactive imagination.

Ramachandran reported that one colorblind synesthetic subject perceived “Martian colors” that he had never seen with his eyes: his visual brain was being stimulated nonoptically. Could someone whose visual brain was being stimulated in a way correlated to a video camera perceive “Martian colors,” too? Sony just got a patent on some technology that may allow direct non-invasive neural stimulation with better resolution than transcranial magnetic stimulation.

I think the nearest thing to sensory wierdness that I’ve experienced was a slight disruption of my proprioceptive system. When I approach conditions of sensory deprivation–while laying in a warm bed half-asleep, for instance–I sometimes begin to feel like my limbs can’t decide whether they are toothpick-thin or fat and sausage shaped. The qualium of switching between the perceptions is almost identical to that of looking at certain optical illusions, like deciding what side is the top of a 2-d projection of a wireframe cube. My sister Karen reports having felt the same thing.

Benham’s Top and Fechner’s colors produce a subjective color illusion; no one knows for certain how it works, but it appears that the response rates of cones differs; thus colorblind people should not experience the effect. It also seems to have something to do with motion: I masked off all but a thin strip of the Fechner colors demo, perpendicular to the motion, to see if it was just the flashing that caused it. The colors all disappeared for me.

The vOICe is an application that converts images to sound. The vertical axis becomes pitch, while the horizontal becomes time; intensity becomes volume. Users consistently report the sound-as-sight becoming unconscious, and one late-blind person reports that her brain reconnected the input with her visual cortex. She perceives the sound as sight, and even experiences depth due to perspective! I think that if there were two cameras directing different input to each ear, the brain might even do a comparative depth perception.

Haidinger’s brush is a yellow-vs-blue cross due to the concentric circles of the dichroic molecule Lutein around the fovea. Almost anyone can learn to see polarized light with a little practice. I’ve seen it on my LCD screen at work. I haven’t seen it in the sky yet, though.

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2 Responses

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  1. mike said, on 2005 April 13 at 9:22 pm

    The latest DNRC newsletter has a bit on sensory wierdness:

    “Alert readers have noticed that Dilbert looks different lately, almost as if someone else is drawing it. Well, it’s still
    me, but here’s what’s happening: I lost the use of my right hand for drawing, thanks to overuse. Technically, it’s called a
    focal dystonia. It’s essentially a brain-mapping problem caused by overusing the hand. The hand is structurally healthy and
    perfectly fine for every possible use EXCEPT drawing. It’s very specific. My brain essentially removed from me the ability
    to do the thing that was hurting it.

    One way I can confirm that it’s a brain issue is that when I try to draw with my LEFT hand, my RIGHT hand spasms
    immediately. Some part of my brain doesn’t want me drawing because that’s what caused all the discomfort.

    For a few weeks I worked left-handed. I’m not quite ambidextrous, but if I work slowly, it looks about the same. Some of
    the lefty ones have a “L.H.” on them to tip you off.

    Left-hand drawing was too slow, so I looked for, and found, a technical solution. Wacom has a product that allows you to
    draw directly onto a special flat computer screen that tilts and turns just like paper on a drawing board. It’s called the
    Cintiq 21UX, and I’ve been using it for the past several weeks, with much success. It will take a while for my characters to
    look the same as old, but I’m closing in on it.

    The reason I can draw on the computer, but not on paper, is because now I work at a different scale (larger), and the feel
    of the stylus on the screen is so different from pen-on-paper that my brain doesn’t think I’m drawing, so it doesn’t trigger
    the hand spasms.

    Brains are funny.”

  2. Colorblindness cured « reperiendi said, on 2009 September 18 at 12:39 pm

    […] Following up on my previous comments here, scientists have cured color blindness in monkeys: Neitz’s team injected their monkeys’ eyes […]


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