SENSITIVITY OF INFANTS WITH AND WITHOUT DOWN-SYNDROME TO INTRINSIC DYNAMICS

We examined the way in which infants with and without Down syndrome (D S) adapted their intrinsic dynamics, that is, their spontaneous leg mo vements, to perturbations. Weights totaling 25%, 50%, and 100% of thei r estimated calf mass were attached to one leg as they sat in an infan t seat and moved freely. Particularly at higher weightings, infants in both groups demonstrated bilateral sensitivity and adaptability by in creasing activity level of the unweighted leg relative to the weighted leg. Individual differences in sensitivity thresholds were observed f or both groups, but more infants with than without DS demonstrated min imal overt adaptation to the perturbation. We argue that the capacity to respond differentially to the dynamics of movement contexts is nece ssary for acquiring functional motor skills.