Does the benefit of time for working memory arise at encoding or retrieval?

Extended free time between the encoding of list items enhances immediate memory for serial order. Previous research suggests that this effect is predominantly proactive, free time improves memory for items presented after an extended interval but not for those presented before. This conclusion is based on two key findings. First, in forward serial recall, the benefit of free time increases with the serial position of the items (Mızrak & Oberauer, 2021, Oberauer, 2022b). Second, when a single inter-item interval is lengthened, the additional time primarily benefits items presented after that interval (Lu et al., 2024; Mızrak & Oberauer, 2021). Here we tested these two findings using both forward and random order recall and examined whether the relationship between free-time duration and the serial position of item differs when test order was changed. Our findings replicate the evidence for a proactive benefit of time in most conditions. Additional retroactive benefits of free time were apparent in some conditions. Retroactive benefits were more often observed when test order was random, in particular when participants could anticipate being tested in random order.