Have you ever done something for so long that you see it in your sleep? Perhaps you see Candy Crush pieces flying around you, or the Excel spreadsheet you were working on turns into a giant maze. Then, you wake up and wonder if you have an addiction (or you're working too hard). There's a name for this phenomenon, named after the classic game of connecting geometric shapes—the Tetris effect.
The idea was first put into words by author Jeffrey Goldsmith in a 1994 WIRED article: "At night, geometric shapes fell in the darkness as I lay on loaned tatami floor space. Days, I sat on a lavender suede sofa and played Tetris furiously. During rare jaunts from the house, I visually fit cars and trees and people together." Since then, this so-called game transfer phenomenon has helped scientists explore both memory and brain structure.