Incidental learning of list membership is affected by serial position in the list

Cowan, Donnell, and Saults [(2013). A list-length constraint on incidental item-to-item associations. Psychonomic Bulletin & Review, 20, 1253-1258] examined incidental memory of whether two words had occurred in the same list or different lists, after the lists had been presented with an orienting task that did not require memorisation. Performance was superior for 3-word lists compared to 6- or 9-word lists, with memory for the longer lists near chance levels. Here we re-examine this phenomenon with methodological modifications to ensure that learning was incidental: we removed potential clues that a memory test would follow, eliminated trials with special mnemonic cues related to the orienting task, eliminated participants who suspected a memory test according to a post-experimental questionnaire, used signal detection measures to distinguish between memory sensitivity and bias, and tested list length with the relative serial position controlled. Incidental memory formed primarily for the most recent part of each list, an effect that was stronger than that of list length. The new evidence helps to constrain theories about the relation between working memory and incidental learning. A capacity-limited approach to the incidental-learning process still is possible but must be modified compared to Cowan et al., and the evidence is favourable to other theoretical approaches as well.