Aspects of early social smiling by infants with Down's syndrome.

Smiling by five Down's syndrome and seven nonhandicapped infants was recorded longitudinally during face-to-face interactions with their mothers over the first 6 months of the infants' lives. Two conditions, 'mobile' (mothers were asked to talk to the baby as naturally as possible) and 'immobile' (silent and maintain an impassive face), were contrasted. Between-group comparisons confirmed previous findings of significantly delayed emergence and less frequent smiling by the infants with Down's syndrome. Their smiles were also found to be shorter, and less discriminative between the two face-to-face conditions. The non-handicapped infants showed significantly more cry/distress vocalizations in the immobile than in the mobile condition, while the reverse was found for the Down's syndrome infants. A close temporal association between smiling and eye contact with mothers was found for both groups of infants. In a free interaction condition, mothers of the Down's syndrome babies showed a stronger tendency to use kinaesthetic and tactile stimulation than mothers of the non-handicapped infants.