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Blind Spot

To see or not to see.
The eye’s retina receives and reacts to incoming light and sends signals to the brain, allowing you to see. One part of the retina, however, doesn't give you visual information—this is your eye’s “blind spot.”

Blind Spot Experiment Explo 2

Tools and Materials

  • A few 3 × 5 cards or other stiff paper
  • Black marking pen (felt tip works best)
  • Optional: yard stick or meter stick and a partner
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Assembly

Mark a dot and a cross on a card as shown.

Blind Spot Experiment Explo 2

To Do and Notice

Hold the card at eye level about an arm’s length away. Make sure that the cross is on the right.

Close your right eye and look directly at the cross with your left eye. Notice that you can also see the dot.

Focus on the cross, but be aware of the dot as you slowly bring the card toward your face. The dot will disappear, and then reappear, as you bring the card toward your face. Try moving the card closer and farther to pinpoint exactly where this happens.

Now close your left eye and look directly at the dot with your right eye. This time the cross will disappear and reappear as you bring the card slowly toward your face.

Try the activity again, this time rotating the card so that the dot and cross are not directly across from each other. Are the results the same?

What's Going On?

The optic nerve—a bundle of nerve fibers that carries messages from your eye to your brain—passes through one spot on the light-sensitive lining, or retina, of your eye (click to enlarge diagram below). In this spot, your eye’s retina has no light receptors. When you hold the card so the light from the dot falls on this spot, you cannot see the dot. The fovea is an area of the retina that is densely packed with light receptors, giving you the sharpest vision.

thema-Links

Biology

Human body

Seeing

Senses

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