Take a good look at the image below. Really focus on its center.
After a few seconds, you will notice the pattern starts to fade as if the exposure setting has been ramped up. The lighter colors and the shapes on the periphery will be the first to disappear. Within a minute or so, the picture should have melted into the background, leaving a blank white space (or, perhaps, a gray square).
Until you blink.
As soon as you move your eyes or shift your attention, the image will jolt back into view.
If you are having trouble seeing the effect, ramp the brightness up on your screen.
It's a visual trick called "Troxler's effect" because it was invented by a man called Ignaz Troxler, a Swiss physician, politician, and philosopher who lived at the turn of the 19th century. He had a long and prolific career but is best known for this particular mind-boggler of an illusion.
Of course, the image never really goes away. It is just an illustration of the way our brain copes with the thousands of sensations we are exposed to on a constant basis – a phenomenon known as selective processing. Without us realizing it, the brain filters out extraneous information so that we can focus on the important stuff, say a potential predator shuffling in the bushes or a car turning the corner as we're about to cross the road.
The brain tends to tune out visual stimuli that don't change, hence why the colors fade in the image above. You focus on the center, the brain decides the shapes are unnecessary information, and so mentally "fills in" the space with the surrounding white.
Day-to-day, we probably don't realize this is even happening because our eyes and our surroundings are constantly shifting, psychology professor Derek Arnold of the University of Queensland told The Verge.