Eerie patterns of eye and brain
Q: During night, when it's dark, I rub my (closed) eyes. When I rub in the corner next to my nose, I see something white moving simultaneously with my finger in the opposite corner of my eye. What is that?
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| The eye is an outgrowth of the brain | |
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A: Our brain interprets what we see but sometimes it misses what's really happening. When we close an eye and rub it, many of us see a small white spot in the opposite corner, or possibly a black spot with a white rim, according to Jeremy Wolfe, Harvard Medical School ophthalmology professor. When you rub your finger in your eye, you send a signal to the brain. The brain interprets it as light and, indeed, interprets all signals coming from the eye as light.
Light normally travels to the back of the eye to light receptors and nerve cells in the retina. When the receivers absorb light, they stimulate nerve cells that signal the brain. The brain interprets the electrical signals as an image or simply light. That's what normally happens.
When you rub your eyes, however, you directly stimulate the nerve cells in the retina. The brain nevertheless interprets the messages as light because that's how it's wired. That's why you see something white moving simultaneously with your finger in the opposite corner of your eye. Why the opposite corner?
The optics of the eye inverts the image that shines on the retina. "So if
something stimulates the left side of the retina, the brain is wired up to see
that as coming from the right side of the world," Wolfe says.
(Answered by April Holladay, science correspondent, April 3, 2002)
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