The Importance of Auditory Feedback for the Expression of Emotions in Single Calls and in Call-sequences of Normally Hearing and Hearing-impaired Infants

The aim of the study was to investigate the influence of hearing impairment on the preverbal vocalizations of infants by comparing utterances of normally hearing (NH) and profoundly hearing impaired (HI) infants. First, we focused on the acoustic structure of the three most common call types. Second, we examined the composition of call sequences. In both cases, we analyzed whether there are general differences in vocalizations between NH and HI infants, and whether different emotional states affect the vocal production of NH and HI infants in the same way. Concerning the acoustic structure, we found that only one call type, the cry, showed subtle, but significant differences related to hearing ability. Emotionrelated changes in call structure were the same for both study groups. In contrast, sequence composition was more affected by hearing impairment than the structure of single calls: Independent from the emotional state, HI infants produced some call types (babbling and short cry) less often, and others (coo/wail and croak) more often within a sequence than NH infants. The composition of call sequences uttered by NH infants changed according to emotional context, while there were hardly emotion-related changes in HI infants. These results indicate that the acoustic structure of preverbal call types is to a great extent predetermined, while the composition of call sequences is influenced by auditory input.