Mothers were recorded singing a song of their choice in both a lullaby styl
e and a play-song style to their 6-month-olds. Adult raters identified the
play-song-style and lullaby-style versions with 100% accuracy. Play-song-st
yle renditions were rated as being more brilliant, clipped, and rhythmic an
d as having more smiling and more prominent consonants. Lullaby-style rendi
tions were characterized as being more airy, smooth, and soothing. Adults o
bserved videotapes (without sound) of 6-month-olds listening to alternating
lullaby-style and play-song-style trials and performed at above chance lev
els when determining which music the infants were hearing. Coding analyses
revealed that infants focused their attention more toward themselves during
lullaby-style trials and more toward the external world during play-song-s
tyle trials. These results suggest that singing may be used to regulate inf
ants' states and to communicate emotional information.