Two-year-olds succeed at MIT: Multiple identity tracking in 20- and 25-month-old infants.

Infants' ability to remember objects and their locations emerges during the first year of life. However, not much is known about infants' ability to track objects' identities in a dynamic environment. Here, we tailored the delayed match retrieval eye-tracking paradigm to study infants' ability to track two object identities during occlusion-an infant version of multiple identity tracking (MIT). Delayed match retrieval uses virtual "cards" as stimuli that are first shown face up, exposing to-be-remembered information, and then turned face down, occluding it. Here, cards were subject to movement during the face-down occlusion period. We used complex non-nameable objects as card faces to discourage verbal rehearsal. In three experiments (N = 110), we compared infants' ability to track object identities when two previously exposed cards were static (Experiment 1), were moved into new positions along the same trajectory (Experiment 2), or were moved along different trajectories (Experiment 3) while face down. We found that 20-month-olds could remember two object identities when static; however, it was not until 25 months of age that infants could track when movement was introduced. Our results show that the ability to track multiple identities in visual working memory is present by 25 months.