The first phase of the procedure consists of training, during which, a habit is created by repeated association of the word pairs. Word pairs are presented every 2 seconds as an incomplete pair (door-knobs), then for 1 second as the complete pair (door-knobs). Subjects guess completions that are semantically related to the stimulus word. Unknown to subjects, the word pairs occur with specific frequencies; one pair (e.g., door-knobs) is presented as the correct response in 67% of trials while the other word pair (e.g., door-knock) is presented as the correct response in 33% of trials. Word pairs are presented in random order with the exception that no word pair occurred on more than 3 consecutive trials. The word pairs that are presented at high or low frequency are counterbalanced across subjects.