Introduction

Every mammalian eye contains a scotoma, or a part of the visual field that does not contain input from photoreceptors. Although all humans have scotomas, visual scenes usually appear complete. This activity explores scotomas and attempts to demonstrate how the brain compensates for these parts of the visual field that don’t contain information by removing those items from awareness.

One example of a scotoma is the so-called blind spot in the human eye, which is located where the optic nerve attaches to the retina. Complete the following steps to see for yourself that you have a blind spot in the corner of your eye.

1. Take a piece of paper and draw a small X on the right side.
2. Measure about 12 centimeters to the left of the X and draw a circle the size of a dime (about 1 cm across) at that location.
3. Hold the paper in front of you and close your right eye. Look at the X. You should be able to see the dot out of the corner of your eye.
4. Slowly move the paper in front of you. At a certain point, the dot will seem to disappear out of the corner of your eye.

You can repeat this activity for the other eye by rotating the paper 180 degrees and repeating steps 3 and 4.

All people have scotomas caused by the optic nerve leaving the eye. Some people also have scotomas caused by damage to the retina or damage to the visual cortex. In almost all cases the brain is able to construct what appears to be a complete visual scene by removing the scotoma from awareness.

The following activity will help demonstrate a leading explanation for how the brain compensates for scotomas.

Click on the button to begin.