Abstract 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 infantabsent 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.
Throughout the world caregivers sing to their infants (Brakeley, 1950; Trehub & Schellenberg, 1995; Trehub & Trainor, in press; Tucker, 1984). At times, soothing or sleep is the principal goal, as in lullabies; at other times, play or stimulation is the overriding agenda. In general, the pitch register is lower and the tempo slower in lullabies than in play songs (Trehub & Trainor, in press). Although lullabies are largely confined to soothing and sleep contexts, play songs extend well beyond play contexts, accompanying child care routines such as feeding, diaper changing, and bathing (Trehub, Unyk et al., 1997).
Lullabies are structurally, as well as functionally distinct from other song types, as reflected in the ability of naive listeners to distinguish recorded lullabies from non-lullabies (matched on tempo), even when the songs are from foreign musical cultures (Trehub, Unyk, & Trainor, 1993a). The principal perceptual distinction between a lullaby and non-lullaby, aside from its text and tempo, is the structural simplicity or repetitiveness of the former (Unyk, Trehub, Trainor, & Schellenberg, 1992). In general, musically inexperienced listeners classify a song with slow tempo as a lullaby if its pitch contours are smooth and predominantly descending (Unyk et al., 1992). In deciding what is and what is not a lullaby, listeners do not simply distinguish songs for infants and children from those intended for adults. When vocal cues are unavailable, for example, as in synthesized instrumental versions of songs, listeners can often differentiate lullabies from play songs and from other adult song categories (Trehub & Trainor, in press). For example, adult listeners confuse native American lullabies (instrumental versions) with love songs, which implies that lullabies share some of the structural features of love songs (Trehub, Unyk, Schellenberg, Sr Kamenetsky, in preparation). Vocal rather than instrumental versions would likely reduce or eliminate such confusions.
In a sense, lullabies and play songs are the musical analogues of soothing and playful baby talk or motherese (i.e., infant-directed speech). For example, caregivers' soothing utterances to infants are marked by low pitch, a narrow pitch range, and falling pitch contours; their playful utterances are characterized by brevity, high pitch, wide pitch range, rhythmic regularity, and rising or risefall contours (Beebe, Feldstein, Jaffe, Mays, & Alson, 1985; Fernald, 1989; Fernald & Simon, 1984; Ferrier, 1985; Papousek, Papousek, & Symmes, 1991; Sachs, 1977; Stern, Spieker, & MacKain, 1982). As with soothing and playful speech (Fernald, 1991; Papousek et al., 1991; Stern, Spieker, Barnett, & MacKain, 1983), lullabies and play songs are presumed to regulate infant arousal (Trehub & Schellenberg, 1995; Trehub, Trainor, & Unyk, 1993). Thus, the measure of a successful performance for infants is not critical accolades or applause but rather signs of interest, contentment, pleasant affect, or rudimentary comprehension. …