Long-term memory facilitates spontaneous memory usage through multiple pathways.

Memories scaffold ongoing cognition and behavior.1,2,3,4,5 Surprisingly, when given the "sensorimnemonic" choice6 between using working memory (WM) and sampling sensory information from the environment, reliance on WM is much lower than expected.7,8,9,10,11,12,13 Here, we ask how the availability of long-term memory (LTM), alongside WM, changes how participants spontaneously sample sensory information in service of memory encoding, rely on their memory, and coordinate the two. Participants copied a model display by selecting realistic objects from a resource pool and placing them into a workspace.13,14 We tracked head, hand, and eye movements during free-flowing interactions with the virtual environment. To test the contributions of LTM engagement during natural behavior, we manipulated the repetition of stimulus arrangements over 2 days and used novel arrangements as a baseline. LTM availability had multiple consequences, resulting in an increased reliance on memory content. Further, LTM improved the efficiency of sensory sampling, evidenced by shorter encoding times of repeated objects. In the extreme, mnemonic sampling directly substituted sensory sampling, as some objects were not sampled at all before successful copying in repeated trials. These changes unfolded concurrently within the same task. Finally, incidentally formed memories during the task were accessible for explicit report. Performance in a subsequent surprise memory task showed that participants placed more objects correctly in repeated arrangements. Our findings demonstrate concurrent spontaneous deployment of multiple LTM mechanisms, alongside WM and sensory processing, showcasing impressive flexibility in balancing the engagement of sensory and different types of memory information to guide adaptive behavior. VIDEO ABSTRACT.