Psychologists became aware of the distinction between storage and retrieval as early as the 1930s, when John Alexander McGeoch, a psychologist at the University of Missouri, tasked study subjects with memorising pairs of unrelated words. For example, every time I say pencil, for instance, you say chessboard. That task became far more difficult, he discovered, when, before asking his subjects to recite what they"d memorised, he confronted them with decoy pairs: pencil and cheese, pencil and table. The decoy pairs, it seemed, competed with the true pair for the memoriser"s attention.