This is a fascinating optical illusion. When I first looked at it I thought it was like Herman's Grid and the yellow dots were appearing. As I observed further I realized the yellow dots were actually seeming to disappear. As I focused on an area the yellow dots in adjacent areas disappeared.
"Asagao" The yellow dots placed off the center of sight appear to vanish. "Asagao" is a plant with flowers. Copyright A.Kitaoka 2003
I found this on 52 Optical Illusions & Visual Phenomena, by Michael Bach his page has a wide array of interactive Flash illusions, very well done. Michael Bach refers to "Motion Induced Blindness" by Yoram Bonneh, Alexander Cooperman and Dov Sagi as the source for this illusion. They say the following about this illusion:
Motion Induced Blindness (MIB) is a phenomenon of "visual disappearance" in which salient visual stimuli disappear as if erased in front of the observers eyes. This demo demonstrates several properties of this phenomenon. It is implemented as a set of GIF animation and can only be appreciated if the apparent motion appears smooth or almost smooth. In general, fixate in the center or lower part of the screen without moving the eyes, pay attention to the moving pattern and observe what happens to the static yellow dots.
