Prioritizing Detailed Item Memories Through Post-Encoding Motivation Requires Consolidation

Prioritizing memories that are motivationally salient is adaptive for goal-directed behavior, ensuring that information being retained is the most relevant to future goals. Past research demonstrates we can use value signals to adaptively modulate our memory. Crucially, however, the timing of value signals varies. Sometimes we know the significance of an upcoming event in advance, while other times, we are unaware of an event's importance until after the fact. Does the timing of a value signal relative to encoding change the cognitive mechanism by which it shapes memory? To test this question, we developed a motivated encoding task where the motivational cue appeared either before or after encoding. Across two independent samples, pre-encoding motivation improved item memory regardless of test timing, while the benefit of post-encoding motivation only appeared after a 24-hour delay. For source memory, pre-encoding motivation reliably enhanced performance across conditions. In contrast, the effect of post-encoding motivation on source memory was more variable: it was significant across both test timings in Experiment 2, but was weaker and more variable in Experiment 1. Furthermore, the two conditions differently affected incidental memory organization; pre-encoding motivation enhanced item order memory relative to post-encoding motivation. These results reveal the dissociable effects of pre- and post-encoding motivation, and suggest that when we learn of an event's importance might determine the mechanism by which we can strengthen its memory for future use.