Is infant-directed speech prosody a result of the vocal expression of emotion?

Many studies have found that infant-directed (ID) speech has higher pitch, has more exaggerated pitch contours, has a larger pitch range, has a slower tempo, and is more rhythmic than typical adult-directed (AD) speech. We sh ow that the ID speech style reflects free vocal expression of emotion to in fants, in comparison with more inhibited expression of emotion in typical A D speech. When AD speech does express emotion, the same acoustic features a re used as in ID speech. We recorded ID and AD samples of speech expressing love-comfort, fear, and surprise. The emotions were equally discriminable in the ID and AD samples. Acoustic analyses showed few differences between the ID and AD samples, but robust differences across the emotions. We concl ude that ID prosody itself is not special. What is special is the widesprea d expression of emotion to infants in comparison with the more inhibited ex pression of emotion in typical adult interactions.