You are doing it right now. Although you are totally unaware of it yet, your brain is flipping everything it sees right-side up. Without this brain flip, your world would look as topsy-turvy as the images cast upon your retina.
But suppose an image was somehow projected right-side up. Would your brain know the difference and keep the scene as it appeared? Or would it perform a flip and turn the image upside down? Find out in this cool experiment.
Things Required:
Pin
Index card
Directions:
Use the pin to poke a small pinhole in the centre of the index card. Stand in front of a brightly lit window. Hold up the card several inches from your face. Look through the hole at the bright outdoors.
Hold the pin so that its flat head may extend upwards. Position the pin head between the hole of the card and your eye. First, hold the pin at a level just beneath the hole. Slowly, raise the pin head. From which direction does it appear to cross the pinhole? Keep the pin head centreed in the hole. Describe its appearance.
This Is What Happens:
Most of the time, the light rays that cast an image cross as they stream through the eye’s pupil. This produces an upside-down view that your brain has learnt to flip around.
In this experiment, you’ve created a unique set-up. The rays that come through the pinhole won’t cross over themselves. They only spread out. As they stream through the pupil, they remain uncrossed and cast a right-side up image on the retina. Your brain, however, has learnt to flip over everything that it sees. So even though the image projected right-side up, your brain flips it upside down!
