The extension of the interference effect to multiplication.

Using multiplication facts, this experiment demonstrated an interference effect in the number-matching task. Here, subjects verified the presence of a target number (e.g., 8) in a previously presented cue (e.g., 5 x 8) that was masked after 60 ms. The SOAs between cue and target were 100, 120, 220, and 350 ms. Subjects were slower to reject targets that were the product of the cue (e.g., 40) than to reject unrelated targets (e.g., 42), but this was true only at the 100- and 120-ms SOAs (i.e., the interference effect). This pattern is consistent with the interference effect found by LeFevre and colleagues using addition facts. Furthermore, the present result supports the interpretation that the interference effect previously found with addition facts was due to obligatory activation and not to automatic counting.