Frequency of vocalization before and after cochlear implantation: dynamic effect of auditory feedback on infant behavior.

The motivation for infants' non-word vocalizations in the second half of the first year of life and later is unclear. This study of hearing infants and infants with profound hearing loss with and without cochlear implants addressed the hypothesis that vocalizations are primarily motivated by auditory feedback. Early access to cochlear implants has created unique conditions of auditory manipulation that permit empirical tests of relations between auditory perception and infant behavior. Evidence from two separate tests of the research hypothesis showed that, before cochlear implantation, infants with profound hearing loss vocalized significantly less often than hearing infants; however, soon after cochlear implantation, they vocalized at levels commensurate with hearing peers. In contrast, vocal behaviors that are typically considered reflexive or emotion-based signals (e.g., crying) were infrequent overall and did not vary with auditory access. These results support the hypothesis that auditory feedback is a critical component motivating early vocalization frequency.