The Tetris effect (also known as Tetris syndrome) occurs when people devote so much time and attention to an activity that it begins to pattern their thoughts, mental images, and dreams. It takes its name from the video game Tetris.
People who have played Tetris for a prolonged amount of time can find themselves thinking about ways different shapes in the real world can fit together, such as the boxes on a supermarket shelf or the buildings on a street. They may see coloured images of pieces falling into place on an invisible layout at the edges of their visual fields or when they close their eyes. They may see such coloured, moving images when they are falling asleep, a form of hypnagogic imagery.
Those experiencing the effect may feel they are unable to prevent the thoughts, images, or dreams from happening.
A more comprehensive understanding of the lingering effects of playing video games has been investigated empirically as game transfer phenomena (GTP).
The Tetris effect can occur with other video games. It has also been known to occur with non-video games, such as the illusion of curved lines after doing a jigsaw puzzle, the checker pattern of a chess board, or the involuntary mental visualisation of Rubik’s Cube algorithms common amongst speedcubers.
The earliest example that relates to a computer game was created by the game Spacewar! As documented in Steven Levy’s book Hackers: “Peter Samson, second only to Saunders in Spacewarring, realized this one night when he went home to Lowell. As he stepped out of the train, he stared upward into the crisp, clear sky. A meteor flew overhead. Where’s the spaceship? Samson thought as he instantly swiveled back and grabbed the air for a control box that wasn’t there.” (p. 52.)
Robert Stickgold reported on his own experiences of proprioceptive imagery from rock climbing. Another example, sea legs, are a kind of Tetris effect. A person newly on land after spending long periods at sea may sense illusory rocking motion, having become accustomed to the constant work of adjusting to the boat making such movements (see “Illusions of self-motion” and “Mal de debarquement”). The poem “Boots” by Rudyard Kipling describes the effect, resulting from repetitive visual experience during a route march:
’Tain’t—so—bad—by—day because o’ company,
But—night—brings—long—strings—o’ forty thousand million
Boots—boots—boots—boots—movin’ up an’ down again.
There’s no discharge in the war!
— Rudyard Kipling, Boots
Mathematicians have reported dreaming of numbers or equations; for example Srinivasa Ramanujan, or Friedrich Engels, who remarked “last week in a dream I gave a chap my shirt-buttons to differentiate, and he ran off with them”.