Divided attention during encoding causes separate memory traces to be encoded for repeated events

Strengthening some items on a list adversely affects memory for the remaining items on the list – a phenomenon known as the list-strength effect (LSE; e.g., Tulving & Hastie, 1972). Whether the LSE is observed depends on how memory is tested and how items are strengthened (Malmberg & Shiffrin, 2005; Ratcliff, Clark, & Shiffrin, 1990), with free recall producing robust LSE, whereas recognition test typically producing null LSE. In this report, we examined the LSE in free recall and recognition when items were learned with full attention or under divided attention at encoding. In free recall, the results showed a robust LSE under full attention, but a null LSE in divided attention. In contrast, in recognition a null LSE was observed under full attention, but a positive LSE emerged under divided attention. Within REM theoretical framework, the combination of these findings suggests that DA reduces the tendency to accumulate information across repetitions in a single trace, thereby reducing the influence of differentiation.