Effects of Hearing Status on Adult Speech Production

In the Hearing Status project, we measure changes in speech production that occur in response to changes in hearing. These studies are focused on three populations of adults. The first are participants with normal hearing. Second, are those who learned to speak, then lost hearing and finally regained some hearing with a cochlear implant. Third and last are patients with bilateral acoustic neuromas, a few of whom lost their hearing during the course of the project (This work was funded by a separate NIH grant from 1991 to 1995.) As stated above, we hypothesize that the internal model controlling speech production is acquired in childhood with the use of auditory feedback. In adulthood, it is used to program speech movements essentially "open loop" - that is, without the speaker being influenced by the sound of his or her own voice. However such auditory feedback does come into play to make adjustments in the internal model that are necessitated by changes such as growth of the vocal tract or receiving dentures. Our studies have shown that speech intelligibility remains remarkably intact in postlingually deafened adults, even decades after hearing loss - consistent with open-loop control. On the other hand, we have also shown that speech does deteriorate somewhat with hearing loss, and acquisition of some hearing from a cochlear implant usually leads to some normalization of speech parameters, including measures of speech respiration, vowel and consonant spectra and voicing onset time. These improvements are most observable in those cochlear implant users who show improvements over time in speech perception.