Stare, then see a ghost
The pictures your eyes leave behind.
How this site works. Every fact is in our own words and linked to its source, beside it. Where good sources disagree, we show each version in a “Sources differ” box. Every picture is our own drawing: we don’t copy the famous originals, we make our own versions of the idea.
What is an afterimage?
An afterimage is an illusion in which the picture on your retina lingers after the thing itself has gone. Britannica
It can be positive, matching the original, or negative: less bright, or in the complementary colours. Britannica
A common one is the spot you see after a camera flash. Britannica
Try it: the flag
Stare at the dot in the middle until the timer ends, then keep looking at the same spot.
An afterimage normally fades within a few seconds. Michael Bach
Research has traced the afterimage to retinal ganglion cells, in the eye itself. Michael Bach
We normally move our eyes about three times a second, so afterimages rarely build up in everyday life. Michael Bach
The lilac chaser
In the lilac chaser, a ring of magenta blobs circles a cross, and one blob at a time briefly disappears. Michael Bach
Keep your eyes on the cross and you see a green spot running round the ring. Michael Bach
With a really steady gaze the magenta blobs fade away completely, leaving only the green spot. Michael Bach
Your brain joins the afterimages, one place after the next, into a single moving green disc. Michael Bach
Its inventor, Jeremy Hinton, says it shows Troxler fading, complementary colours and negative after-effects. Michael Bach
Bach notes that the opposite colour of red is not green, as many textbooks say, but blue-green. Michael Bach
The McCollough effect
The McCollough effect: after a few minutes of looking at coloured stripes, black and white stripes look faintly coloured. Michael Bach
Most aftereffects last a minute at most. This one can last hours. Michael Bach
Ten minutes of adapting is said to give an effect lasting months. Michael Bach
Bach warns that trying it changes your brain for a long time, up to months. Michael Bach
Because it can last so long, we don’t include a McCollough demo here.
Our view: an afterimage is a tiny peek at your eye at work. It isn’t broken; it is busy getting used to things.
Next: Benham’s spinning top →