Listeners' perception of lexical stress in the first words of infants with cochlear implants and normally hearing infants

Abstract

Normally hearing (NH) infants are able to produce lexical stress in their first words, but congenitally hearing-impaired children with cochlear implants (CI) may find this more challenging, given the limited transmission of spectro-temporal information by the implant. Acoustic research has shown that the acoustic cues to stress in the first words of Dutch-acquiring CI infants are less pronounced (Pettinato, De Clerck, Verhoeven, & Gillis, 2017). The present study investigates how listeners perceive lexical stress in the first words of CI and NH infants. Two research questions are addressed: (1) How successful are CI and NH children in implementing the prosodic cues to prominence? (2) Is the degree of stress in CI and NH words perceived to be similar? The stimuli used in this study are disyllabic words (n = 1089) produced by 9 infants with CI and 9 NH infants acquiring Dutch. The words were presented to adult listeners in a listening experiment, in which they assessed the stress pattern on a continuous visual analogue scale (VAS) which expresses to what extent syllables are perceived as stressed. The results show that listeners perceive typical word stress production in the first words of infants with CI. The words of CI and NH infants were rated in agreement with the target stress pattern as often, and trochaic words were rated more frequently as such than iambic words. Listeners more frequently perceive unstressed syllables in the first words of infants with CI. However, for the words that are perceived to be clearly stressed, the degree of word stress is comparable in the two groups, and both infant groups are perceived to produce more contrast between stressed and unstressed syllables in trochees than in iambs. It is concluded that that acoustic differences between CI and NH infants' stress production are not necessarily perceptually salient.