Testing working memory benefits long-term memory only when paired with re-exposure

Testing long-term memory (LTM) is well known to enhance subsequent retention beyond mere re-exposure effects. Recent evidence suggests that testing during working memory (WM) also boosts LTM performance. However, it remains unclear whether these WM testing benefits are a consequence of retrieval or reflect increased familiarity due to re-exposure. In this preregistered study, we aimed to distinguish between these two. Participants memorized four images in their corresponding locations for a subsequent WM test. During this test, an image was presented in one of the memory locations, and participants had to determine whether it matched the memory (retrieval and re-exposure) or not (retrieval but no re-exposure). In an additional color-task condition, the image was presented in a red or green frame, but now participants simply determined the frame color (re-exposure only). Finally, in a no-test condition, no test was presented at all (neither retrieval nor re-exposure). Following an interruption, participants then completed a surprise LTM test involving a two-alternative forced-choice test between one old and one new image. LTM accuracy was higher for an item from the match condition than from the color-task condition, indicating a benefit of WM testing beyond re-exposure. Re-exposure alone also enhanced performance compared to no test. However, LTM performance in the non-matching test condition was no better than the no-test condition, suggesting that testing without re-exposure did not enhance LTM. Together, these findings suggest that while re-exposure benefits retention by itself, testing in WM boosts LTM only when paired with re-exposure to the target item.