Comparing vocal parameters in spontaneous and posed child-directed speech

Research on the facial expression of emotion distinguishes between correlates of posed vs. spontaneous emotion expression. Similar research in the vocal domain is lacking. In this study, we compare changes in a range of vocal parameters between posed vs. spontaneous adult-directed (AD) and child–directed (CD) speech. CDS is a highly affectively charged speech register which lends itself well to the study of posed vs. spontaneous emotion expression. A group of mother addressed an adult and their child, and a group of non-mothers addressed an imaginary adult and an imaginary child. The results confirm adjustments in pitch, formants and speech rate typically reported for CDS in both groups. At the same time, they show that source parameters not in service of linguistic function, such as shimmer (perturbations in fundamental period amplitude) and harmonics-to-noise ratio show clear group effects suggesting that they may constitute veridical indicators of spontaneous emotion expression.