Do semantic and phonological categories lead to proactive interference in immediate and delayed serial recall tasks?

Proactive interference (PI) has received considerable attention in research on working memory (WM), but empirical findings have been mixed. The present study examined whether this inconsistency may partly reflect the distinction between item and order memory. We hypothesized that PI would be more evident in item memory than in order memory and tested this hypothesis by applying item and order memory scoring methods to serial recall tasks. We also systematically manipulated two types of categories (semantic and phonological) and two recall tasks (immediate and delayed serial recall). For semantic categories, PI effects were consistently observed in item memory: performance increased following category shifts (e.g., animal words vs. flower words) in both immediate recall (Experiment 1A) and delayed recall (Experiments 1B and 3). In contrast, for phonological categories, reliable PI effects in item memory were observed under delayed recall (Experiment 2B), but not under immediate recall (Experiment 2A). Across these experiments, no clear PI effect was observed in order memory. These findings support the hypothesis that PI is more evident in item memory than in order memory and further suggest that the type of information may also influence PI. We also discuss how our delayed task relates to and differs from the Brown-Peterson task, a well-established task used to assess PI, in light of the item-order hypothesis. The distinction between item and order memory appears to be key to understanding PI in WM and may provide a useful framework for synthesizing past findings and guiding future research.