Sleep and testing both strengthen and distort story recollection

Over time, memories lose episodic detail and become distorted, a process with serious ramifications for topics such as eyewitness identification. What are the processes contributing to such transformations over time? We investigated the roles of post learning sleep and retrieval practice in memory accuracy, transformation, and distortion, using a naturalistic story recollection task. Undergraduate students listened to a recording of the “War of the Ghosts”, a Native American folktale, and were assigned to either a retrieval practice or listen-only study condition, and either a sleep or wake delay group. A significant interaction for accuracy was observed between delay group and study condition, with higher accuracy after sleep compared to wake, but only in the absence of retrieval practice. However, sleep and retrieval practice also led to more inferences of non-presented, but story related information, via a second significant delay group by study condition interaction. These findings suggest that both sleep and retrieval practice contribute equally to narrative memory stabilization and distortion.