Related memories exhibit interference during learning in adults but later retrieval in children.

To build knowledge, learners of all ages must relate new information to their past experiences. While the interactions among prior and new memories have been extensively studied in adults, they are not yet well characterized in children. There are reasons to expect that children and adults may differ substantially in how related memories interact when memories are first formed as opposed to later referenced, but this has yet to be directly assessed. Here, we had children (4-16 years old) and young adults learn new object locations which either could or could not be incorporated into previously learned two-dimensional maps, i.e., initial memories. Afterwards, they retrieved initial maps from memory. Importantly, initial and new learning occurred on the same day, allowing us to characterize how related spatial memories interact when acquired close in time. We found that during learning, adults but not children were impeded by their recent memories such that they were slower to learn locations within a previously encountered map. However, the opposite developmental pattern emerged at retrieval: Children but not adults demonstrated interference such that they remembered an initial map worse after they had formed new memories within it. Overall, our results suggest that while children and adults may both experience interference among related memories, this interference manifests at different stages: during learning for adults but later memory retrieval for children.