Paradoxical decrease of imitation performance with age in children

We studied the development of imitation ability in a cohort of 6-11-year-old children (N=174) with specific attention to error types and to their cognitive interpretation. Participants imitated meaningless actions as if they were in front of a mirror (specularly). Actions varied across three levels of complexity (movements of a single limb, of arm and leg of the same body side, or of arm and leg of opposite sides). Overall performance improved with age. Among the most frequent error categories, “side” errors (movement imitated with the left instead of the right limb or viceversa) paradoxically increased with age (from 9 years), but their sensitivity to complexity decreased with age. Thus, encoding two opposite body sides has high cognitive costs in younger children, and smaller or null costs in older children. We interpreted these results in terms of enhancement of Working Memory (WM) and body knowledge with age. When WM increases, it paradoxically drives older children to apply their superior body knowledge and imitate "anatomically", producing side errors. Younger children are free from such interference because they still lack the necessary body knowledge and WM capacity. The (fewer) side errors made by younger children would be due to failure to manage the conflict between opposite spatial codes, an effect of limited WM capacity witnessed by their sensitivity to action complexity. In conclusion, this study suggests that anatomical imitation becomes available in children’s cognitive repertoire from age 9, as an effect of increased body knowledge and WM capacity.