Parents' sung performances for infants.

Naive listeners rated the style of singing in mothers' and fathers' sung performances for infants and their simulations of those performances (Experiment 1). Performances in an infant's presence were judged as more expressive--either more playful or more soothing--than were simulations. Parents' style of singing, as reflected in these ratings, differed as a function of the sex of singer and listener. Both parents sang more playfully for same-sex infants than for opposite-sex infants. Independent listeners rated the manner in which parents enunciated the lyrics of their songs (Experiment 2). Parents rendered the lyrics of songs more expressively in infant-present than in infant-absent contexts. Moreover, this expressiveness was greater for same-sex infants than for opposite-sex infants. These findings are consistent with parents' greater attachment to same-sex infants. Discrepancies between parents' choice of songs and their manner of singing lend credence to functional rather than nominal classifications of songs for infants.