Picture-evoked changes in pupil size predict learning success in children

Episodic memory, the ability to remember past events in time and place, develops during childhood. Much knowledge about the underlying neuronal mechanisms has been gained from methods not suitable for children. We applied pupillometry to study memory encoding and recognition mechanisms. Children aged 8 and 9 years (n = 24) and adults (n = 24) studied a set of visual scenes to later distinguish them from new pictures. Children performed worse than adults, demonstrating immature episodic memory. During memorization, picture-related changes in pupil diameter predicted later successful recognition. This prediction effect was also observed on a single-trial level. During retrieval, novel pictures showed stronger pupil constriction than familiar pictures in both age groups. The statistically independent effects of objective familiarity (previously presented pictures) versus subjective familiarity (pictures evaluated as familiar independent of the prior presentation) suggest dissociable underlying brain mechanisms. In addition, we isolated principal components of the picture-related pupil response that were differently affected by the memorization and retrieval effects. Results are discussed in the context of the maturation of the medial temporal lobe and prefrontal networks. Our results demonstrate the dissociation of distinct contributions to episodic memory with a psychophysiological method that is suitable for a wide age spectrum.