Structural alignment facilitates the noticing of differences.

High-similarity concept pairs that elicit many commonalities also elicit many related differences (Gentner & Markman, 1994; A. B. Markman & Gentner, 1993a, 1993b, 1996; A. B. Markman & Wisniewski, 1997). This finding has been used to support the claim that the comparison process is one of structural alignment. However, it is possible that the difference advantage results from some other property of high-similarity pairs, such as a greater number of stored differences. The present experiments demonstrate that the comparison process itself leads to the greater psychological availability of differences. In three experiments, participants listed commonalities for word pairs and then listed differences under a time pressure for these old pairs and new pairs. In Experiment 1, participants listed more differences for old than for new pairs, consistent with the claim that the comparison process facilitates noticing differences. In Experiment 2, we showed that the difference-listing advantage is specific to the comparison process: Mere coprocessing of the pairs (specifically, providing thematic relations) does not facilitate, and in fact appears to inhibit, difference listing. In Experiment 3, pairs with deeper common systems elicited a larger number of specific alignable differences than did pairs with shallow sets of commonalities. Overall, the results support the structural alignment claim that the comparison process promotes the noticing of both commonalities and related differences.