Eyelids. They come in handy for sandstorms, eye shadow, and poolside naps. You don’t see much when they’re closed, but when they’re open you have an all-access pass to the visible world around you. Right? Well, not exactly. Here at Garden of the Mind, the next two posts are dedicated to the ways that you are blind – every day – and with your eyes wide open.
One of the ways you experience everyday blindness has to do with the movements of your eyes. If you stuck a camera in your retina and recorded the images that fall on your eye, the footage would be nauseating. Think The Blair Witch Project, only worse. That’s because you move your eyes about once every half a second – more often than your heart beats. You make these eye movements constantly, without intention or even awareness. Why? Because, thanks to inequalities in the eye and visual areas of the brain, your peripheral vision is abysmal. It’s true even if you have 20/20 vision. You don’t sense that you are legally blind in your peripheral vision because you compensate by moving your eyes from place to place. Like snapping a series of overlapping photographs to create a panoramic picture, you move your eyes to catch different parts of a scene and your brain stitches these ‘shots’ together.
As it turns out, the brain is a wonderful seamstress. All this glancing and stitching leaves us with a visual experience that feels cohesive and smooth – nothing like the Frankenstein creation it actually is. One reason this beautiful self-deception works is that we turn off much of our visual system every time we move our eyes. You can test this out by facing a mirror and moving your eyes quickly back and forth (as if you are looking at your right and left ears). Try as you might, you won’t be able to catch your eyes moving. It’s not because they’re moving too little for you to see; a friend looking over your shoulder would clearly see them darting back and forth. You can feel them moving yourself if you gently rest your fingers below your lower lashes.
It would be an overstatement to say that you are completely blind every time you move your eyes. While some aspects of visual processing (like that of motion) are switched off, others (like that of image contrast) seem to stay on. Still, this means that twice per second, or 7,200 times each hour, your brain shuts you out of your own sense of sight. In these moments you are denied access to full visual awareness. You are left, so to speak, in the dark.