This week's experiment is an old classic, but it is one
that always amazes me. Each of your eye's has a
blind spot. A small area where you cannot see. What amazes me
is not that there is an area that you can't see, but that you can't see the
"hole" in your vision. Instead, your brain
fills in the space, so that you don't notice it. The only way to
see it is to position a small object directly into that spot and notice that it
disappears. To try this, you will need:
This web page
Your eyes
In the space below, you will see an X and an O. Sit with the page (either
printed or on your screen) about 24 inches from your eyes. Cover your left
eye and with the right one, stare directly at the X.
Move the X towards your face (or your face towards the screen), always
staring directly at the X. When you reach a certain point, the O will
vanish. If your shift your eyes to look for it, it reappears. Look
back at the X and it is gone again.
X
O
You can try this with your left eye too, using the O instead of the X.
What is happening? On the back of your eye is a layer
of light sensitive
cells called the retina. When light hits these cells, it stimulates
your brain and you see. To carry the information from the retina to your
brain, you need a large nerve. It is called the optic nerve. At
the point where the optic nerve comes through the retina, there is a hole, a
spot with none of the light sensitive cells. That is your blind
spot. It is off to the side of your field of view, in the area where
things are not in sharp focus. Instead of seeing a "hole" your
brain fills in the space. For this reason,
you don't notice that things disappear when they are in this part of your
vision, unless you are really watching for it to happen.
So did you find your blind spot? Tell us your results on the poll!
This experiment was re-printed with permission from Robert Krampf