The melody of surprise : maternal surprise vocalizations during play with her infant.

Two groups of mothers and their infants (24 infants, mean age=3.5 months and 24 infants, mean age=5.5 months) were video- and audio-taped in their homes while playing with a Jack-in-the-box. The mean fundamental frequency of spontaneous surprise exclamations of mothers when opening the toy were analysed, and infant and maternal facial expressions of surprise were coded in three regions of the face. A t-test established that significantly more of the older children in comparison with younger children showed surprise (t=-2.96, df=46, p