Art & Aesthetics Art Blog
The Mechanics of Vision and Eyesight
by art_aesthetics , September 11, 2008—12:00 AM
Beauty is in the eye of the beholder whether you're looking at an Ingres' odalisque, a Grecian urn, a Gibson arch-top, or Gucci heels. For everything from Delacroix to dirty pictures, you need vision to enjoy art.
As I have my head examined by the experts here at The Peterson Institute of Arts and Sciences Research Laboratory and Gift Shop, my eyeball is a theme park. Let me walk you through it while the venerated Doctor D. L. Rayburn stands by on the outside. So don your wet-suits for a trip thru the vitreous humor, the fluid that fills the eyeball - but please, no flash photography. If hypodermic needles and quivering eyeballs make you squeamish then just relax and...
We're in. You can take off the rubber suits and put on these - whoa! Hang on, the orb is rotating. Let me check the eye movement control center in my forebrain. Mental note: Wow! I must have developed X-ray vision. Look at the frontal lobes on that gal in the...well, let's not get sidetracked.
Dr. Rayburn, please prop my eyelid back up. We can use the light in here.
O.K. folks, don't trip over the plumbing but turn your attention to the back wall - that's the retina. It receives light that enters the eye in the form of photons. I see a hand. Yes, the young lady with the long legs and short lab coat. -- you have a question?
"Are photons like fireflies?"
Photons are balls of energy that cause chemical change in the vision cells that send electric signals to the brain, so - yeah. Very few photons ever reach the retina. They bounce off of the cornea or get lost in the gumbo. Those that make it form patterns on the retina -- that shag carpet of cells well-connected to the brain. We're talking about a network that makes a yuppie want to yodel.
Let's watch a photon come in the window. Doctor Rayburn will now bounce a single photon of light off of an unidentified object with a photon gun. Here's the wind-up, and the pulse, and -- holy smoke, what a humdinger! Ouch. That corpuscle had some heat on it. It hit the fovea and turned it into a smoldering tar pit. Dr. Rayburn must have had it set on "stun." Keep that in mind at the next laser light show. Let's cross over to the other eye. Watch your heads passing through the optic chiasma - the bridge between the left and right brain - and slide down into the fresh peeper. When we look at something, we focus on a point in front or beyond an object to spread our vision evenly on it - a blank stare, not to be confused with the "male gaze." Contours, contrast, and color gives us clues as to what it is, but details require pin-point focus and eye movements. The eye darts from one point of interest to the next: winks, smiles, and plump protrusions, but you can't see the whole until you look past the parts.
If you focus on the letter "x" in the word "fixation," everything else becomes background "noise." The eyes must work to see everything in view. One seldom looks that hard unless, say, someone calls to you at a crowded gallery opening or you misplace your suitcase full of cash at the airport. When they have to, your eyes will find what they're looking for. But beware; the eye also goes to the weakest link: a toothless grin or a fly in the Chardonnay.
That little satellite dish in the middle of the retina is the fovea. It's packed with cones but no rods. Cone cells resolve details and colors. Rods see shapes in dim light. We can see faint stars or shadowy creatures in the night if we don't look at them - at least not directly. An off-center glance aligns the weak light signal with the rod cells outside of the fovea. For depth perception, humans have their eyes on the same side of the head. Picasso portraits may have two eyes on the same side of nose.
Here comes another photon from the mystery image. Dr. Rayburn throttled back for this pink puff-ball. Yet, the plucky photon tickles a cell and sends a signal into the brain through that little hole in the wall, the optic nerve.
Yes, the man in the hardhat and galoshes - a question?
"So the optic nerve is like a funnel?"
More like a battery of sodium and potassium that propels a charge along the axonal membrane deep into the brain where the cells all share information in a parallel process that computers can't even dream about. A computer strings images together like beads on a loom. The human eye builds a scenario in the order of visual interest - angles, outlines, nice buns - by flexing six orbital muscles to survey the world. The brain puts a subjective spin on everything we see. In fact, I feel strangely aroused right now. Let's follow that impulse along this coaxial cable towards the big screen theater in the back of my head - the visual cortex.
A physicist will say the primary colors are red, blue, and green while an artist says magenta, cyan, and yellow. Whom to believe -- the Poindexter in a lab coat or the Bohemian in a smock? Both. One applies to light and the other to pigments.
"So colors are light that is either reflected or absorbed?"
Well, what an honor -- it's the Intellectual Handyman. Welcome, sir. You must have snuck up on the service elevator. As you well know, the additive synthesis of - hey, where'd the old geezer go? He blended in with the grey matter. Well, never mind him - where's the gal with the gams?
"Hang on - I'm coming." Ah, 'she's like a raaiiin-bow...she comes in colors...' "What are you singing?" It's a Rolling Stones song. "Who?" No, Stones. "Who's that?" The same guys that wrote 'Paint It Black.' "Wow. How old are you?" Let's just catch up to the signal. The pulse enters a gizmo: the lateral geniculate nuclei. It's a color filter. Reducing three-color signals down to one is what these opposing cells do -- sort of like a Polaroid camera. Now, smile everybody...Whoa! Flashbulb.
Our perky little voltage spike zips along towards a synapse. We're not talking "Grand Canyon" here, just a half millionth of a centimeter. But no sparks cross these gaps, just chemicals called neurotransmitters. Drugs like LSD can unlatch synaptic gates and allow stray signals into restricted regions of the brain causing short circuits that can make us smell sounds or taste colors. I don't recommend that. The impulse strikes a bundle of nerves like a billiard ball scattering signals towards the farthest pockets of the brain. Which shall we follow? I'll check a roadmap of this cerebral landscape - the throbbing blobs of neural cells, the thick and thin, pale and rich stripes of the brain. There's the anterior cingulate cortex for art aesthetics and the basal ganglia for hand-eye coordination. It's quite a sight on the way to sight. Doctor Rayburn, I noticed some atrophy above the anterior vermis of the cerebellum. That's right - schizophrenia. Write me a prescription, will you? On the up side, I think I saw my sense of humor lurking near the amygdale. Certain brain cells are feature detectors. They know what they're looking for and what to do when they find it. A feature cell is hardwired to fire, say, only when light falls in a straight line across the retina - or an arc, or a right angle heading north by northwest, but many cell groups are needed to construct a visual perception. There is no single brain cell with grandma's face on it. The internalization of any picture is abstract. It's not a connect-the-dots affair. If we mapped the brain cells involved in "seeing" an image, it would include most every stripe, gap, bulb and lobe in this three pound organ. You can't look at a picture book of presidents and expect to see Abe Lincoln projected inside of your skull. Ditto the swimsuit issue of Sports Illustrated, but that's where a photographic memory pays off. Fortunately, my brain has a mind of its own. I think.
Uh oh, we're lost. Let's split up into teams and rendezvous later. You guys take that path. Miss Firefly and I will head south and meet you in the thalamus. This way we can cop a feel for the parallel processes of vision.
"Excuse me, but I know what you're thinking, Son of Pete or whoever you are." How do you know what's on my mind? "We're knee deep in it."
O.K., well I see this morning's lost tour group is straggling in, so let's compare notes with them and see what we can make of this single red photon we've been tracking. When I flip this switch labeled "Gestalt," the sparking tangle of static electricity and the electrochemical traces of memory, cognizance, and emotion pulsing through my perception engine will complete the whole visual perception and light up the sum of its parts so you can all see what I see - the big picture. Here goes, and voila...
Look, everyone! It's Doctor Rayburn - the lovely Doctor Dorothy Rayburn. Hello Doctor Dot. It's nice to see - gad zooks, woman! You performed the whole procedure dressed like that -- just a logo T-shirt, latex gloves, and anti-static platforms like the ones available in many colors and sizes in the Gift Shop open weekdays and Sunday noon 'til four? Hot couture!!
Peep show's over, folks. This concludes our tour of the pathways to visual perception. Thank you and come again to The Peterson Institute of Arts & Sciences Research Laboratory & Gift Shop where you get a free bumper sticker with every paid admission. Please exit single file through the pupils while I try not to blink. Now, everybody - out of my head
COMMENTS
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09/15/2008 * 07:42:39
Zander / Michael
Thanks, guys. Your comments are very charitable regarding this feverish piece of jabberwocky. Yes, my brain must have been gapping but I feel much better now.
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09/13/2008 * 22:44:47
Thanks for the tour! Our next field trip should be to your brain so we can try and figure out exactly what is going on up there. We might want to bring along the intellectual handyman though, I suspect you might have a couple of misfiring synapses!
sofa ( homepage )
05/01/2012 * 08:37:01
Hi
The Mechanics of Vision and Eyesight
Fascinating views on that! very informative, Great looking site you have here and great post too.
Thank you!