This study investigated five acoustic parameters of fundamental frequency (f0), one related to average f0 level and four related to change of f0 (f0 change) over four consecutive quarters of the vocalic segment, for their roles as acoustic correlates to the perception of Cantonese lexical tones produced by profoundly hearing-impaired speakers.
Speakers were 20 Cantonese adolescents, 10 of whom had normal-hearing (mean age = 13;05); the other 10 were profoundly hearing-impaired (mean age = 13;05). The hearing-impaired speakers were selected on the basis of the criterion of being prelingually deaf; they showed pure-tone average thresholds of 90 dB HL or more in the better ear at 0.5, 1.0, and 2.0 kHz. Twenty-four consonant-vowel Cantonese words made up four sets of words that minimally contrasted in the six contrastive Cantonese tones. The words were read by the speakers once in random order. Listeners were 10 final-year speech therapy students who were asked to identify the Cantonese tones. The f0 of each syllable (tone) was measured at five consecutive positions of the vocalic segment (initial, 25%, 50%, 75%, final). Discriminant analysis was used to determine how average f0 and f0 change accounted for both the production of intended tones and the perception of correctly identified tones.
Average f0 and f0 change over the second half of the vocalic segment were reliable acoustic and perceptual correlates of tones produced by control speakers. By contrast, for hearing-impaired speakers, production of intended tones were not reliably distinguished by average f0 or f0 change. Furthermore, listeners mainly relied on f0 change over the second half of the vocalic segment for the distinction between tone 25 and level tones (55, 33, and 22) produced by hearing-impaired speakers.
Average f0 and f0 change over the second half of the vocalic segment are important cues for accurate identification of Cantonese tones produced by speakers with normal-hearing. By contrast, these cues are less reliable for perceiving tones produced by profoundly hearing-impaired speakers.