So far, the afterimages in this slide show have been filled in with colors and brightness. But what happens when you adapt to a dynamic stimulus? The Twinkle effect shows that when a static object adapts to a dynamic surround, the static areas may appear as dynamic. Fixate your gaze on the center point to adapt to the snow (vision scientists call it “dynamic noise”). Notice that the gray square is slowly replaced with dynamic noise, until the entire background appears as dynamic noise. When the dynamic noise in the surround is then extinguished, you will see a twinkling afterimage where the gray square used to be: this is the Twinkle aftereffect. This illusion shows the amazing extent to which the brain works to adapt to the world around us. Even in the presence of constant change, our visual system produces complementary and continually changing adaptation effects. Various aspects of this effect were discovered by Vilayanur S. Ramachandran (of the University of California San Diego), Richard Gregory (University of Bristol, U.K.), Lothar Spillmann and A. Kurtenbach (Frieburg University, Germany).

Vision scientists Michael Crossland, Steven Dakin, and Peter Bex have used the Twinkle illusion to characterize blind spots caused by retinal damage in patients with macular degeneration (the most common form of blindness for patients over age 50).