Effects of Age and Cochlear Implantation on Spectrally Cued Speech Categorization

Abstract

Purpose Weighting of acoustic cues for perceiving place-of-articulation speech contrasts was measured to determine the separate and interactive effects of age and use of cochlear implants (CIs). It has been found that adults with normal hearing (NH) show reliance on fine-grained spectral information (e.g., formants), whereas adults with CIs show reliance on broad spectral shape (e.g., spectral tilt). In question was whether children with NH and CIs would demonstrate the same patterns as adults, or show differences based on ongoing maturation of hearing and phonetic skills. Method Children and adults with NH and with CIs categorized a /b/–/d/ speech contrast based on two orthogonal spectral cues. Among CI users, phonetic cue weights were compared to vowel identification scores and Spectral-Temporally Modulated Ripple Test thresholds. Results NH children and adults both relied relatively more on the fine-grained formant cue and less on the broad spectral tilt cue compared to participants with CIs. However, early-implanted children with CIs better utilized the formant cue compared to adult CI users. Formant cue weights correlated with CI participants' vowel recognition and in children, also related to Spectral-Temporally Modulated Ripple Test thresholds. Adults and child CI users with very poor phonetic perception showed additive use of the two cues, whereas those with better and/or more mature cue usage showed a prioritized trading relationship, akin to NH listeners. Conclusions Age group and hearing modality can influence phonetic cue-weighting patterns. Results suggest that simple nonlexical categorization tests correlate with more general speech recognition skills of children and adults with CIs.