The McCollough effect is a phenomenon of human visual perception, in which black, white and colours appear to change. Warning - watch with caution.
Discovered in 1965 by Celeste McCollough, the effect has been described in a video which warns that looking at the image for 15 minutes can cause a visual disturbance that lasts up to three months.
A warning appears on the video, which was created by Tom Scott of Things You Might Not Know, that the McCollough effect could potentially permanently rewire a human brain.
Working on a cognitive rather than retinal level, the two squares of horizontal and vertical different coloured lines can leave an individual seeing white gratings.
The effect is different from colored afterimages, which are superimposed on whatever is seen and which are generally quite brief.
Scott warned that the video should be watched with caution.
In the video, he says: "There is an idea in literature called 'harmful sensation', the idea that a sight, a pernicious idea, a sound, a song, can get into your head and stay there for a very long time and actually do you harm.
"Pernicious earworms aside, there is actually a real thing that can get inside you head and affect the way your brain works. It's called the McCollough effect.
"I realise that telling people on the internet not to do something is like telling a five-year-old not to stick beans up their nose, but seriously if you work with text or video, don't do this"
"It's quite scary, it's a real image that can lock into your brain, change the way it works and stick around for a good while."
He explains: "If you stare at these images for long enough, you'll get - as you would with blank colours, the opposite appearing in your brain. If you stare at a green light for long enough, you'll see red for a little while afterwards."