To make a floating, phantom white dot appear on the right-hand side, look at the black dot on the left for about 20-seconds. Count to yourself, or use the handy timer below.
When the time is up, look directly at the black square on the right. You will soon see an image of a white dot; an afterimage of the black dot.
These affects are not harmful, and may indeed have therapeutic benefits.
Notes
Displays a still image. The “timer below” is a separate java applet and is not included here.
Alt titles
The Floating White Dot
Source
http://www.sandlotscience.com/Aftereffects/Floating_White_Dot.htm (via web.archive.org)
Floating White Dot screenshots
