The Tetris effect occurs when an activity to which people devote sufficient time and attention begins to overshadow their thoughts, mental images, and dreams. It is named after the video game Tetris. In the game a player rotates and moves different falling tetrominoes, or shapes made up of four adjacent square blocks. If the player can arrange the shapes so there are complete horizontal lines of blocks without any gaps, those lines are eliminated. The aim of the game is to eliminate as many lines as possible before the shapes ultimately fill the screen.
People who play Tetris for a prolonged amount of time may then 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.[1] In this sense, the Tetris effect is a form of habit. They might also see images of falling Tetris shapes at the edges of their visual fields or when they close their eyes.[1] In this sense, the Tetris effect is a form of hallucination. They might also dream about falling Tetris shapes when drifting off to sleep.[2] In this sense, the Tetris effect is a form of hypnagogic imagery.