Abstract
Object exploration affords rich opportunities for learning across the first years of life. During object play, infants use different combinations of fingers, different roles for each hand, and will deconstruct object parts-these fine-grained differences comprise the construct manipulation complexity (MC). We examined MC in a sample of 90 typically developing infants (47 males; 75% White) assessed at six monthly visits from 9-14 months of age from a battery of eight objects. Guttman analyses found that MC is cumulative, meaning that infants can do the most complex manipulation skill if they are able to also do all the lower ranked manipulation skills. The order from least complex to most complex was: (1) bimanual manipulation, (2) bimanual manipulation with distinct roles for each hand, (3) object deconstruction, and (4) independent digit movement. These results introduce a new framework for describing fine motor skills in infant manipulation.