Maintenance of phonological contrast in speech production of cochlear implant users

Abstract

Prior work has shown that normal-hearing (NH) talkers produce more distinct vowels in words having a lower word frequency (WF) and higher neighborhood density (ND). Phonological contrast in speech production may differ between post-lingually deafened cochlear implant (CI) users and individuals with NH due to the degraded auditory input provided by CIs. The current study sought to determine whether the same pattern of vowel production exists in CI users. CI users were recorded reading monosyllabic words that were lexically “hard” (low WF, high ND) or “easy” (high WF, low ND). For each participant, vowel dispersion was calculated as the Euclidian distance from the center of the acoustic vowel space. If degraded acoustic input affects phonological contrast in CI users, we would not expect vowel dispersion to differ between vowels in “hard” and “easy” words, contrary to talkers with NH. Preliminary results revealed a significant effect of lexical difficulty on vowel dispersion, indicating that CI users produced more distinct vowels in “hard” words than in “easy” words. These preliminary findings could suggest that degraded auditory input does not substantially affect phonological contrast in vowel production in CI users, or that long-term adaptation to CI input can restore contrast after auditory deprivation.