This applet demonstrates an orientation afterimage. Press the space bar and stare at the image. It will be shown for 20 seconds and be replaced by a blank screen.
The afterimage is observed as a shimmering circular percept. These complementary afterimages suggested the presence of neurons in visual cortex that were sensitive to oriented edges. Neurophysiological recordings later verified this prediction.
These afterimages have been independently discovered many times, with each discussion starting with a phrase like "I am sure someone has already noticed this, but I cannot find any mention of it..." Interestingly, the reports are in top journals like Psychological Review, Science, and Nature, but apparently go unnoticed.
The most recent discovery of the afterimage was made by MacKay (1957) in a report in Nature. The afterimage is often referred to as MacKay afterimages, although he called them complementary afterimages. To see the stimulus again, press "i" and then the space bar.