Tradeoffs between item and order information in short-term memory

Recently, Guitard et al. (2021) used a two-list procedure and varied the kind of encoding carried out for each list (item or order encoding). They found that dual-list impairment on an order test was consistently greater when the other list was also encoded for an order test, compared to when it was in the presence of another list encoded for an item test. They also found a dual-list cost relative to one list, for both order and item information. Here we address the bases of the interference costs with a novel task in which, prior to each list presentation, participants were instructed to expect an item fragment completion test, an order reconstruction test, or either type of test. In five experiments, we contrast two competing accounts of item and order processing, the conflicting representation hypothesis and the common resource hypothesis. An asymmetry with larger dual-attention costs on order compared to item tests was found, with the effect magnitude changing with task conditions. Our results support a version of the common resource hypothesis in which both item and order processing occur no matter which test is expected, but in which additional processing is divided between item and order codes in a manner that depends on task demands.