Sex differences in social responsiveness between six months and twelve months.

14 male and 14 female infants were observed interacting with their mothers for 4 min in a free-play situation at 6, 9, and 12 months, using a cross-sectional design. Both mother and infant initiations of interaction and responses to the other's initiations were recorded using an observational technique similar to that used by Clarke-Stewart. There were no age or sex differences in either maternal responsiveness or the number of attempts the mothers made to initiate interaction with the infants. Although no sex difference in responsiveness was observed when the mother used toys to elicit the infant's attention, girls were significantly more responsive when the mother merely spoke to them (vocal initiations). The frequency of social initiations made by the infants increased significantly from 6 to 9 months, but at all 3 ages girls initiated more interactions than did boys. These sex differences in sociability did not reflect differences in the amount of time spent manipulating toys, nor did they reflect sex differences in the frequency of vocalizations, although between 6 and 9 months there was a significant increase for both sexes in the percentage of vocalizations which were used to initiate interactions.