Vocal expression of emotions in normally hearing and hearing-impaired infants.

The vocalizations of seven normally hearing (NH) and seven severely hearing-impaired (HI) infants were compared to find out the influence of auditory feedback on preverbal utterances. It was tested whether there are general differences in vocalizations between NH and HI infants, and whether specific emotional states affect the vocal production of NH and HI infants in the same way. First, the acoustic structure of the three most common vocal types was analyzed; second, the composition of vocal sequences was examined. Vocal sequence composition turned out to be more affected by hearing impairment than the acoustic structure of single vocalizations. This result indicates that the acoustic structure of preverbal vocalizations is to a great extent predetermined, whereas the composition of vocal sequences is influenced by auditory input.