Development of Object-Based Working Memory from 10 to 16 Months: A Longitudinal Study Using the “Magic Box” Manual Search Task

Object-based working memory is a fundamental cognitive ability that allows us to encode, store representations of, and use information about objects that are no longer present across short time scales. There is currently a lack of longitudinal research on how this ability develops in infancy. In the present pre-registered study, we used a manual search task, the “Magic Box” task, to assess infants’ ability to represent one or more hidden objects. Across several trials, between 1 and 4 objects were hidden in a box and the number of objects retrieved by the infant on each trial was recorded. Furthermore, on half the trials, 1 object was surreptitiously removed to test whether infants would search longer when they expected 1 more object in the box than was actually in there. The same group of infants completed the task at 10 months (N = 141) and 16 months (N = 75). Results indicated that the capacity to represent objects in working memory increased between 10 months (~1 object) and 16 months (~2 objects). Both age groups searched longer when an object had been secretly removed than when no objects were removed. Increased capacity was also demonstrated by 16-month-olds searching the box significantly longer than 10-month-olds on trials with one object missing, indicating a stronger representation of the ‘missing’ object. However, performance at 10 months was not predictive of performance at 16 months, suggesting instability in individual differences in object-based working memory capacity across this period.