Dissociable contributions of reward and surprise to long-term memory

Reward and surprise recruit dopaminergic systems that support memory formation, yet their combined contribution to declarative long-term memory remains poorly understood. We leveraged music as a naturally rewarding and statistically structured stimulus to test how subjective reward and model-derived surprise interact during encoding to promote long-term memory. Seventy-five participants listened to and rated unfamiliar classical musical excerpts in an in-person behavioral paradigm. Reward was indexed by subjective pleasure ratings, and surprise was quantified using a validated computational model able to capture musical predictability. Memory was assessed after 24 hours using recognition and recollection measures. Reward and surprise each enhanced recognition memory, and both effects remained significant when modeled jointly despite their positive association. However, the interaction between reward and surprise predicted the likelihood of providing a Remember or Know response rather than a Guess response. This suggests that their combined effect does not merely increase recognition, but enhances the subjective certainty of the memory trace. In other words, when an item is both rewarding and surprising, participants are less likely to rely on guessing and more likely to report either recollection of specific details or a strong sense of familiarity. Together, these findings suggest that subjective reward and model-derived surprise contribute in a graded and interactive manner to long-term memory for music: each facilitates recognition, but their convergence enhances the likelihood of a more confident form of memory expression. This interaction may help explain how new songs become rapidly memorable or “stick in our heads” even after a single exposure. More broadly, the results suggest that pleasurable and unexpected experiences are especially likely to be encoded as durable memories.