Thinking inside the box: Mental manipulation of working memory contents in 3- to 7-year-old children.

We developed a non-verbal task assessing updating and manipulation of working memory contents. 80 3- to 7-year-olds (47 girls; predominantly European White) were tested with a 4 × 4 grid containing 8 boxes (in the 4 centre cells and 4 outer corners). A sticker was hidden and children searched for it after a delay phase. In the updating trials, the grid was rotated during delays, in the manipulation trials, the grid was both occluded and rotated. Rewards were hidden in either the inner or outer boxes (between-subjects design). Performance was affected by age, rotation degree and hiding condition. Performance was better in outer boxes trials, where visual tracking was easier. Occluded inner trials added a substantial cognitive load (which increased with degree of rotation), resulting in children performing at chance level, suggesting that manipulation involving mental rotation is a distinct skill from tracking invisible object displacement, with a more protracted development.