Objective: This study aimed to evaluate the role of spectral fine structure and envelope information in Mandarin tone perception for sensorineural hearing-impaired patients.
Methods: The linear predictive coding technique was applied to synthesize 128 tokens having spectral fine structure from one tone of a monosyllabic word and spectral envelope from other tones with the same syllable. There after, the tone response performance was assessed using these 128 speech materials for 20 normal-hearing and 48 sensorineural hearing-impaired patients, including 20 with moderate, 20 with moderate to severe, and 8 with severe hearing loss.
Results: 99.7%, 97.7%, 96.3% and 83.0% of the mean tone responses were consistent with spectral fine structure for the normal hearing, moderate, moderate to severe, and severely hearing-impaired groups, respectively. No tone recognition responses were observed in consistent with spectral envelope cues. There was a significant difference in tone recognition among the normal hearing group and three hearing impaired groups (χ(2) = 59.2, P < 0.001). The negative correlation between the averages for pure-tone hearing thresholds at frequencies of 500, 1000, and 2000 Hz and tone responses that were in consistent with spectral fine structure for the hearing-impaired subjects (r = -0.643, P < 0.001).
Conclusions: For both normal-hearing and hearing-impaired subjects, spectral fine structure plays an important role in tone recognition, and the impact of changing spectral envelope cues on tone recognition is negligible, when spectral fine structure cues are present. Sensorineural hearing impaired patients showed a progressive decrease in the recognition of lexical tones based on spectral fine structure cues, as their hearing loss becomes more severe.