The Tetris effect is a perceptual phenomenon that occurs when people spend extended periods of time playing video games. The phenomenon is called the Tetris effect because it was first noticed by players of the game Tetris. After these players spent hours and hours playing Tetris, which involves moving different shaped configurations of blocks around so that they fit together into neat rows, they found that when they reemerged into the real world, the gameplay had restructured their thought processes, the way they saw and experienced their surroundings; the line between the game world and the real world had blurred. When they closed their eyes to go to sleep at night, the players would see hazy afterimages of the colored configurations falling slowly in interlocking patterns, building imaginary towers which rose into the sky higher and higher and then fell as they fit together and the rows of blocks cleared, the game going on and on against the black screen of their minds without their control, without them being able to quit.

—Justin Wolfe’s “The Tetris Effect”