The Tradeoff Between Item and Order Information in Short-Term Memory Does Not Depend on Encoding Time

Participants can optimize encoding of an immediate verbal memory test for item or for order information, or they can try to be ready for either type of test. Dividing encoding between both kinds of information, however, comes at a cost. Recently, it has been shown that the cost is more severe for order information compared to item information (Guitard et al., 2022). Here, for the first time, we evaluated which factor can better account for this asymmetry by contrasting two hypotheses. According to a rate hypothesis, divided attention affects the rate of encoding more for order than for items. According to an alternative, asymptote hypothesis, divided attention does not affect the rates but diminishes the endpoint, or asymptotic level, of order encoding more than item encoding. In three experiments to distinguish these hypotheses, participants prepared for an item fragment completion test, an order reconstruction test, or both types of tests, in trials with different durations of presentation. Overall, our results were better accounted for by a model which assumes that dividing attention between preparation for item and order testing affects the asymptote of encoding more for order than for items, with no effects on the rates of order or item encoding compared to preparation for a single test. The findings not only replicate our prior results, but also demonstrate that the allocation of attention to item or order processing can be disentangled from the time on task. Public Significance Statement When remembering a list of items, information about the items (such as ingredients in your favorite recipe) and their order (such as which ingredients to add first, second, and so on) are important theoretically and practically. Here we show that the way attention is divided between words and their list order is stable regardless of whether each item is presented for a short time (fraction of a second) or a relatively long time (several seconds). In all cases, attention proves to be more critical for order information in short-term memory, a finding relevant to many cognitive activities (including communication, eating, and learning).