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Experiment No. 6

Your Blind Spot

The body produces its very own electricity. Instead of wires, an electric current travels down nerves taking messages to all parts of the body . One very special nerve is the optic nerve and it can be found at the back of the eye. It takes the picture which the eye sees to the brain – where it is converted into an image which we can recognize and understand. At the very back of the eye, there are special cells that detect colour and black and white. However, there are no light detectors (rods and conns) at the exact point where this nerve can be found. This experiment helps us to find this amazing ‘blind spot’.

Experiment: To find the part of your eye that has literally a 'blind spot'.

Materials:

You will need:

One piece of white paper
A dark coloured marker or pencil

 

Method:

1) Draw a cross on the left side of your page and a circle on the other side.

2) Colour or shade in the two shapes.

3) Hold the piece of paper just in front of your face place your right hand over your right eye.

4) Stare (concentrate!) at the circle while moving the paper away from your face.

Result: What happened?
The cross disappears when the paper is a certain distance from your eyes.

Conclusion: The image of the cross is focused on the eye's blind spot - the part where the optic nerve leaves the back of the eye. There are no light sensitive cells here and the cross disappears.

Try it with the '+' and 'o' below. Just use your computer screen and move your head back until one of the shapes disappears. Remember to keep one of your eyes covered with your hand. If you are staring at the '+' sign on the left, cover your left eye. If you chose to look at the 'o' on the right, cover your right eye.

So two eyes are better than one! Normally, you don't have an eye covered - therefore you don't miss anything, even if something is focused on your blind spot! Our next experiment really shows that two eyes are better than one!

For more blind spot and general sight experiments, click here!

For experiments on light (including some optical illusions), please click here.

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