February 14, 2010 — Every university has a classic course, one with a professor or subject matter that becomes the stuff of campus legend. At Kansas State University, where I got my undergraduate degree, that class was Appreciation of Architecture. The waitlist each semester was massive, but Professor Seamon always managed to squeeze in everyone who wanted to come. We’d sit back and relax in the darkened lecture hall as he showed photos and regaled us with colorful commentary on everything from a tiny park in New York City to the rose window of Notre Dame. “When you walk in and see those colors, it’s just like being high,” he’d say, year after year. After a long pause punctuated by gasps and giggles, he’d continue huffily, “Well, it was the 60’s, you know!”
It seems that Jeremy Wolfe, a professor of ophthalmology at Harvard Medical School and a senior lecturer at MIT, might give Professor Seamon a run for his money with his wildly popular visual-perception seminar on “Ten Things You Can Learn by Poking Yourself in the Eye.” I had hoped to find a video of the lecture, but we’ll have to settle for descriptions of some of the experiments.
* Please be careful as you do these experiments, and be aware that you might end up with a headache by the end of them. Pace yourself! :) *
1.) Partially close one eye. Press gently against the eyelid, near your tear duct (the inner corner).
1.) Partially close one eye. Press gently against the eyelid, near your tear duct (the inner corner).
You should see a flash of light in the opposite corner of your eye. It may take several tries to press the right spot, so don’t despair if you don’t see it at first! I finally succeeded when I focused my eyes about two feet in front of me on the table and pressed gently against the inside corner of my eyelid using my pinkie. Be sure you’re pressing the lid, not the bottom rim—my initial mistake since I was thinking about my tear duct. I saw the flash in my peripheral vision, and it seemed to be a dark blue blob with a neon green rim.
So, what’s going on? Your brain interprets signals from your nerves based on their location in your body. The brain will interpret a tactile signal from your hand as a touch, for instance, while a signal from certain nerves in your ear will be interpreted as a sound. While your brain will register the tactile signals from your eye as you press it as touch, you’re also putting pressure on your retinal nerves; and signals they send to the brain are interpreted as light.
That explains the flash, but why is it on the opposite side of where you press? You may recall that light passing through the lens of the eye is bent in such a way that an incoming image appears upside down and backward on the retina. The brain then flips the image back to normal. When you press on your eye and “create” light, the same process occurs, and you see the flash on the side opposite the eye you pressed.
Though this doesn’t tie directly into this experiment, I can’t help but mention a fascinating study which found that the brain can quickly learn not to re-flip an image. In the study, participants wore glasses that inverted incoming images before they reached the eye. The image would then be inverted as it went through the lens of the eye and end up right-side-up on the retina. At first, the brain flipped the image just as it normally would, resulting in the participants seeing an upside-down world. After a few days, though, the brain learned not to flip the image, and participants’ vision was returned to normal. Upon removing the glasses, the brain had to re-learn to flip the retinal image.
Back to the experiment, consider the mechanical stimulus that would be applied to the retinal nerves if you were to be punched in the eye or, less violently, to rub your eyes vigorously. The brain would interpret the signals as light, and you’d “see stars.”
2.) Close both eyes. Gently rub the outside corner of one eye. Press harder, still rubbing.
You’ll probably see (or maybe “sense” is a better word here) either a white spot or a black spot with a white rim. As you’ve probably guessed, this experiment is similar to the first, with the mechanical stimulus being interpreted as light. You may notice a bluish tint to the spot, an effect due to the stimulation of the rods (rods and cones being the eye’s light-sensitive photoreceptors) distributed around the corners of the eye.
3.) Make fists of your hands and, like a kid throwing a fit or in desperate need of a nap, vigorously rub your eyes. (Tears, screaming, and kicking around on the floor are optional!)
See an undulating checkerboard of sorts? According to neurophysiologists, certain cells in the brain register certain shapes—vertical lines for one set of cells, horizontal lines for another, etc. If you rub your eyes vigorously, the overload of random stimuli will light up the cells for all the shapes at once. That’s the waving checkerboard you see.
4.) Instead of rubbing, trying using your fists/fingers to push straight back on your eyes. (Gently!) Hold the pressure for several seconds.
Eventually, you should see black and white checkers, possibly with variation in the size of the squares. I had a bit of trouble getting this to work, so be patient if you're struggling. It's very cool when you get it! I succeeded when I turned my fists outward (palms away), uncurled my index and middle fingers one notch, so to speak, and used from the knuckle to the first joint of the two fingers on each hand to press back. The effect became clear after about four seconds.
Professor Wolf doesn’t have a definite explanation for the checkerboard, though he suggests that it may be that you’re looking at your own visual cortex, the part of the brain which handles vision. A potential explanation for the variation in square size, which presumably went from small in the center to large at the edges of your field of vision, is that you’re seeing the organization of the visual cortex. It may be that the small, central squares represent detail-intensive cells, while the larger edge squares represent “big-picture” cells. While you may think it’d be great if the visual cortex had the detail-intensive cells throughout the whole field of vision, your brain just couldn’t handle that much information.
If you’re a migraine sufferer, this checkerboard effect may already be familiar. According to Professor Wolfe, it is almost certain in your case that you’re seeing of the visual cortex.
5.) Focus on a certain object. Keeping your eyes open and still focusing, slowly press on one eyelid.
Did the object appear to move? I got the best effect when I focused on a wall hanging across the room, then used my index finger to press the top of my eyelid, close to my eyebrow. Maintaining the pressure, I moved my finger toward my nose, resulting in a dramatic shift of the wall hanging’s apparent position. Neat! Though your eye itself was stationary (assuming you pressed gently), the pressure you applied stretched your eye muscles. The brain interprets the stretches as movement of the eye. The brain then does its best to interpret the same visual input from the perspective of a mistaken “new’ eye position, and you end up seeing the object move.
Eye Can’t Take It Anymore!
It seems Professor Wolf is right that you can learn a good many things from a poke or two in the eye, but I’ve tested the previous eye experiments so much that all I want to do now is give my poor eyes a rest! If only I could slip into the soothing darkness of the old Appreciation of Architecture lecture hall…
References
- Kluger, Jeffrey and Rowan, Karen. Want to Learn Biology? Have Someone Punch You in the Face. Discover Magazine, Body Special Issue. September 14, 2008.
- Thomson, Elizabeth A. How to interpret a poke in the eye. MIT Tech Talk, Volume 37, Number 20. January 27, 1993. Keywords: Eye, Visual Cortex, Brain
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