Find your blind spot

PERCEIVING COLOURS

Locate a part of your eye that does not detect light at all

Details:

• Ages: 10-12+

• Time: 10 minutes

• Learning Outcome: Find your blind spot in right and left eyes.

• Colour Concepts: There are no cones or rods on our retina at the optic nerve. This means we cannot receive/absorb light onto that part of our eye, and we have a ‘blind spot’ in our field of vision.

Materials:

• Thick white paper or cardboard, cut into 3x5” rectangle

• Black magic marker

Instructions:

• On the piece of 3x5 paper, draw a dot and cross (X) as shown in Figure 1.

• Hold the paper at arm’s length, with the same orientation as shown in Figure 1.

• Look at the dot on the left, and close your right eye. Notice how you can see both the dot and the cross.

• While keeping your right eye closed and looking at the dot with your left eye, slowly bring the card closer to your face. The dot should remain directly in front of your left eye. What happens to the cross?

• Now extend the paper at arm’s length again, and this time look at the cross on the right. Close your left eye.

• While keeping your left eye closed and looking at the cross with your right eye, slowly bring the card closer to your face. The cross should remain directly in front of your right eye. What happens to the dot?

• Try rotating the card, so the dot and cross are at an angle of 90 degrees. Repeat the exercise. Do you get the same results?

Vocabulary:

• Blind spot, Retina, Optic nerve

Questions & observations:

• At some point, the cross (or dot) will disappear as you bring the card closer to your eye. Why does this happen? This area where the cross (or dot) disappears locates your blind spot.

• Why does the cross (or dot) not disappear if the card is rotated by 90 degrees?

• Why do we not notice our blind spot in our everyday lives?

• What information does the blind spot give us about the structure of our eye?

What’s going on?

• In order to see, light enters our eyes and is absorbed by our cones or rods, which are located at the back of our eye on the retina.

• The ‘blind spot’ is a small circular area at the back of the retina where the optic nerve enters the eyeball and which is devoid of rods and cones and is not sensitive to light. This means we cannot receive/absorb light onto that part of our eye, and we have a ‘blind spot’ in our field of vision.

• Our brain will ‘fill in’ the missing information from our blind spot so that we have a seamless visual field, and do not notice that information is missing.

Find out more:

• See Parts of the eye entry in the glossary

• Check out the Exploratorium’s “Science Snack” for more information on this exercise: https://www.exploratorium.edu/snacks/blind-spot