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 play video puzzle games like this for a long time may see moving images like this at the edges of their visual fields, when they close their eyes, or when they are drifting off to sleep.
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 colored 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 colored, 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).