Infant manipulation complexity trajectories as predictors of language outcomes at 2 years of age.

Motor development during infancy provides opportunities for social interactions in a changing environment, which in turn, has been linked to the emergence of language and communication. Using the theoretical framework of developmental cascades, we examined whether infant motor trajectories, measured as manipulation complexity (MC), could predict later language skills. Ninety typically developing monolingual English infants were assessed for manipulation complexity at six monthly visits from 9 to 14 months of age from a battery of 8 objects. MC was scaled from 1 to 8 based on all possible combination of the following actions: (i) unimanual or bimanual manipulation; (ii) synchronous or asynchronous use of the hands; (iii) dependent or independent finger use; and (iv) whether the hands manipulated one object or multiple objects. Average MC scores from each month were used in analyses. Trained observers administered the Preschool Language Scales 5th edition when children were 2 years old. Latent class growth analysis identified two infant MC classes: high MC and average MC. MC classes predicted 2-year language skills. Children in the high MC class had higher expressive and receptive language scores relative to children in the average MC class. Results have implications for unraveling the mechanisms underlying motor-language cascades.