This article applies to:
Experiment Author: Susan Campbell. Adapted from STEP and used with permission of Brian MacWhinney
The place where the optic nerve attaches to the eyeball is not sensitive to light. Therefore, in each eye, there is a space in vision where the eye does not actually see. The brain, not being fond of leaving holes in vision, fills in this spot with whatever is around it (or, if both eyes are open, with data from the other eye).
This demonstration allows participants to see where their blindspot is and some basic types of filling-in that the eye does to compensate for that. Low-level patterns like lines, for instance, are completed, whereas high-level patterns, such as evenly spaced circles, are not.
This experiment presents a series of optical illusions designed to pinpoint participant blindspots. Participants sit a little more than a foot from the screen and cover their right eye. Fixate on the white square on the right side of the screen. In each picture, adjust the position of your head and continuing to fixate on the white square. These adjustments will allow the black circle to disappear from view. There is no time limit. There are nine different patterns in this experiment.
Ramachandran, V.S. (1992). Blind spots. Scientific American, 266(5), 86-91.