Consider patients with anterograde amnesia, who cannot consciously recall new experiences in their lives. If you spend an afternoon trying to teach them the video game Tetris, they will tell you the next day that they have no recollection of the experience, that they have never seen this game before—and, most likely, that they have no idea who you are, either. But if you look at their performance on the game the next day, you’ll find that they have improved exactly as much as nonamnesiacs. Implicitly their brains have learned the game: The knowledge is simply not accessible to their consciousness. (Interestingly, if you wake up an amnesic patient during the night after he has played Tetris, he’ll report that he was dreaming of colorful falling blocks but will have no idea why.)