Why early linguistic milestones are delayed in children with Williams syndrome: late onset of hand banging as a possible rate-limiting constraint on the emergence of canonical babbling

In the present study, eight children with Williams syndrome were observed every 2 weeks between 6 months and 30 months of age when interacting with their mothers. When the collected data were transcribed in terms of both linguistic and motor activities, overall delay was found in terms of the onset of canonical babbling,first words, as well as various motor milestones in every child. The degree to which acquisition of each of the milestones was delayed was individually variable. Nevertheless, the onset of hand banging was found to be an indicator that predicted the onset of canonical babbling consistently among the children. Once canonical babbling was produced, moreover, the onset of first words was recorded during a following 2 to 3 month period. These findings appear to indicate the possibility that development of the motor ability to perform such rhythmic motor activity as hand banging acted as a control parameter for production of canonical syllables in the children.