Wide-eyed Wonder: an artist's musings on three-dimensional vision

Some are color blind. I am stereo blind.

Non-stereo Notes from the Flatlander Hairdresser

with 3 comments

I cut my own hair, and I don’t see 3D. Describing my process will be a great introduction into non-binocular depth cues.

First off: I avoid using electric clippers like the little guy on the left! Scissors work best for longer hair, and are more tactile.

Half of hair cutting is tactile, involving the sense of touch. We stereo blind are very gifted at judging distance by touch. So the act of pulling small sections of hair perpendicular to my head to the same distance as the section before is almost intuitive. It involves a sense of timing, too. There’s a sort of steady rhythmic slowness as I run my hand along my scalp, feel a section and slide my fingers up and out and hold, maybe on a subconscious count of three, then snip using the tops of my fingers as a guide.

Secondly, I can judge distance by 2D sight because I have trained myself to do so as an artist and graphic designer. The act of drawing translates the 2D world I see to a 2D canvas or monitor. So I can see 3″ long hair horizontally, vertically and even at an angle with foreshortening, and still intuitively know it is 3″ no matter the angle. (This is mostly known as linear perspective.)

Hairdressers have other tricks, like cutting off the same amount of hair from the ends. “How much do you want me to take off?” is a common question. Once they have taken that amount off one section, they pull up a part of that section into the next, and use it as a guide.

I start my haircut by pulling my hair forward around my face and cutting my bangs and sides where I want the edges to end just under my eyebrows and along my cheekbones. Then I start cutting sections from front to back, using the cut hair as a guide for the amount I wish to take off the rest.

Just like any binocular do-it-yourself hair dresser, I use a mirror on the wall to cut the front and sides. The image of myself that I see is flat, but I still can measure how much to take off and how long the remaining hair is from “3D to 2D conversion” practice. I’m constantly checking by pulling up sections from both sides at the same time at points where the hair is in perfect profile. I’m also studying how the cut hair lays on my head, turning to see if any missed part is sticking out.

I have to move my head to pull each section to a place where I can see it clearly, in perfect profile, usually to the outside edges of the flat image I see of myself. It is also along these edges that I can judge if anything is sticking out.

Since reading about motion parallax, I am moving my head after judging a section length to look at it from more than one angle, as wiki says pigeons do to judge depth [1]. The motion parallax is a new non-binocular cue I am using, and I make less mistakes (I have very forgiving hair!)

Just like the binocular hairdresser, I need a third hand to do the back. I turn my back to the wall mirror and use a hand mirror to see. I no longer need to move my head to gain motion parallax perspective; I can move the hand mirror. I have to put the mirror down to use the scissors, which means I cut by feel, cutting along the tops of my fingers and trying not to take some skin!

I have no clue if this whole experience would be easier in 3D. To you, the reader, I may sound like a square describing how he sees a triangle in the book, Flatland. Or perhaps my way of “seeing” isn’t so radically different after all.

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Written by Lynda Rimke

January 24, 2011 at 12:47 pm

3 Responses

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  1. Nicely done, Lynda. Steven Pinker has a nice description related to what you’re describing, as “Seeing in Two and a Half Dimensions”. It’s about five pages in his marvelous book (How the Mind Works). You can view it through Google via this link, beginning with page 256:

    http://books.google.com/books?id=5cXKQUh6bVQC&pg=PA238&lpg=PA238&dq=Steven+Pinker+Stereo+Vision&source=bl&ots=4Oyry1cV5P&sig=qvYq5sfpGWcSozgOwJi1Q6bB-PA&hl=en&ei=dG4_Te_8B8H98Abp5cCRBA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCQQ6AEwAQ#v=onepage&q&f=false

    As an aside, in view of what we’ve been discussing, that stereovision operates on a continuum, and that it occupies a spot on the real world of depth perception that spatial judgment that is somewhere beteween flatland and binocularly curved space, it is nice to think of the continuum in the current digital parlance. So monocular vision would be vision might be considered version 1.0. Two eyed vision without fusion is version 2.0 Strabismics with good depth judgment based on a reasonable level of volumetric sensitivity would be version 2.5, and full binocular vision would be vision 3.0. Clearly there are many gradations and versions we could further subdivide.

    Len Press

    January 25, 2011 at 8:05 pm

  2. Thanks for the link to the book. Plenty of food for thought here. I plan to go back and chew on it some more as I’m not quite getting exactly why he calls it 2 1/2 D … Here’s my best shot:

    The 2D visual field “sundered by a line” is exactly what I see and that field is curved in the 3rd dimension, too. In fact, my 2.5D is like the walls of a planetarium with a field of focus that can expand and contract. All non-stereo depth cues are taken from that curved movie screen.

    It’s just that your movie screen generates 3D where ever your eyes converge, and mine is does not, because my eyes don’t “converge” only focus. I have depth of field like a camera, but not Panum’s fusional area.

    I have a small fusional area of less than an inch that starts somewhere around 4″ in front of my nose. My eyes only converge there with lots of concentration (or better yet non-concentration :-).

    If I’m a “steroblind 2.5” or 2.8 maybe having a 5′ deep area where my eyes converge would be “binocular 3.0” and full range to the horizon would be 4.0? eg. In his article “Stereo Sue” Oliver Sacks describes losing some binocular vision after being confined to a hospital room. He lost his ability to converge beyond 12′ and had to work to regain fusion to as far as his eye could see once he was out.

    Did you see I’ve added two pages (list in upper right) in an attempt to define some of these things in plain English, so to speak? Since I’ve gone out on a limb because I’m just learning myself, I am WIDE OPEN to any tweaks from professionals to gain
    more clarity ANYWHERE you care to offer a suggestion. I’m a big fan of editing and want to be spot on for my “audience”

    At any rate, I’m happy to cogitate about these things and and sure do enjoy your encouraging comments and feedback in that direction. I also appreciate that you are taking time out of a busy and productive schedule to comment.

    All best!

    Lynda Rimke

    January 25, 2011 at 9:53 pm

  3. Hi Lynda,
    Your descriptions are clear and very intriguing. I can almost imagine walking into the wall, but that came with my experience of trying to ride a bicycle in the dark without even a sliver of moonlight.I’m sure that isn’t the same, but suddenly losing balance when not expecting it, just feels awkward.

    Clicking the book link about learning to see 3D alerted me to something worth checking. My 4 year old granddaughter is wearing a patch, and will be for many years.She spends a lot of time in books and also drawing.

    Mary Helsel

    January 27, 2011 at 4:06 pm


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