The benefit of simultaneous versus sequential presentation of memoranda in working memory: It depends on the stimuli

A relatively large body of research in the working memory (WM) domain has reported a benefit of simultaneous over sequential presentation of memoranda, but this advantage may depend on several factors. Research in visual WM suggests that the advantage of simultaneous over sequential presentation depends on stimulus properties, with simultaneous presentation benefiting simple stimuli and sequential presentation benefiting more meaningful stimuli. The reading literature, on the other hand, suggests that digits may also have a simultaneous presentation advantage, and this particularly when detailed serial order processing is required. The present study examined these assumptions by contrasting simultaneous versus sequential encoding in WM for letter versus digit sequences, and by contrasting item versus serial order WM requirements. In Experiment 1, using an immediate serial recall task, recall performance was higher for simultaneously presented material than sequentially presented material, and higher for digits than for letters. In Experiment 2, a simultaneous encoding advantage and a digit advantage were also observed, as well as a simultaneous presentation advantage that was stronger for digits than for letters. In Experiment 3, the simultaneous and digit advantages remained present when controlling for spatial cues, but their interaction was not supported. These findings indicate that the simultaneous encoding advantage is not reliably modulated by stimulus meaning or by task condition in the verbal WM domain, contrary to predictions derived from the visual WM literature and the reading literature. Taken together, these findings highlight the importance of carefully considering both presentation mode and stimulus type when designing verbal WM tasks and interpreting differences in WM performance across studies.