Processing of Acoustic Information in Lexical Tone Production and Perception by Pediatric Cochlear Implant Recipients

Abstract

Purpose: This study examined the utilization of multiple types of acoustic information in lexical tone production and perception by pediatric cochlear implant (CI) recipients who are native speakers of Mandarin Chinese. Methods: Lexical tones were recorded from CI recipients and their peers with normal hearing (NH). Each participant was asked to produce a disyllabic word, yan jing, with which the first syllable was pronounced as Tone 3 (a low dipping tone) while the second syllable was pronounced as Tone 1 (a high level tone, meaning "eyes") or as Tone 4 (a high falling tone, meaning "eyeglasses"). In addition, a parametric manipulation in fundamental frequency (F0) and duration of Tones 1 and 4 used in a lexical tone recognition task in Peng et al. (2017) was adopted to evaluate the perceptual reliance on each dimension. Results: Mixed-effect analyses of duration, intensity, and F0 cues revealed that NH children focused exclusively on marking distinct F0 contours, while CI participants shortened Tone 4 or prolonged Tone 1 to enhance their contrast. In line with these production strategies, NH children relied primarily on F0 cues to identify the two tones, whereas CI children showed greater reliance on duration cues. Moreover, CI participants who placed greater perceptual weight on duration cues also tended to exhibit smaller changes in their F0 production. Conclusion: Pediatric CI recipients appear to contrast the secondary acoustic dimension (duration) in addition to F0 contours for both lexical tone production and perception. These findings suggest that perception and production strategies of lexical tones are well coupled in this pediatric CI population.

Keywords: children; cochlear implant; cue trading; lexical tone; speech production.

FIGURE 1

The “yan-jing” production, with the second syllable produced as Tone 1 (top) or Tone 4 (bottom) by a 12.7-year-old participant with NH (top two rows) and by a 10.9 year-old participant with a CI (bottom two rows).

FIGURE 2

(Top left and middle) Duration of the two syllables of “yan-jing” produced as Tone 1 or Tone 4, averaged across participants in each population. (Top right) Duration ratios between two syllables indicate that children with CIs prolonged the duration of tone 1 in order to convey what is supposedly a high-flat pitch contour. Error bars show ±1 standard error of the mean. (Bottom) Difference in duration ratio between the two lexical tones, plotted across participants as a function of their chronological age. A greater positive value indicates a stronger tendency to prolong Tone 1 or shorten Tone 4. Regardless of their mode of hearing in everyday life, children with CIs were tested only a single (implanted) side.

FIGURE 3

Mean (thick line) and one standard error (areas) for the intensity patterns extracted for each syllable when producing “yan-jing” with Tone 1 (top panels) vs. Tone 4 (bottom panels). The patterns were delimited in time with a 20-dB cutoff from the intensity peak, and the resulting duration was normalized from 0 to 100% of the total duration to enable averaging across repetitions and participants.

FIGURE 4

(Top-left) Intensity peak of the first and second syllable of the word “yan-jing” spoken as Tone 1 or Tone 4, averaged across all participants in each population. (Top-right) Intensity peak of each tone relative to the syllable preceding it. All children tended to soften the intensity of Tone 1 relative to Tone 4. (Bottom) Difference in relative intensity peak between the two lexical tones, plotted across participants as a function of their chronological age. A lower negative value is indicative of a stronger tendency to soften Tone 1 relative to Tone 4.

FIGURE 5

F0 pattern extracted for each syllable in each tone, with normalized duration (extracted with a 20-dB cutoff from the intensity peak) and normalized in its scale by expressing F0 in semitones relative to the mean over the first syllable. Lines represent the mean over all participants in a given group and areas represent one standard error of the mean.

FIGURE 6

(Top-left) F0 median over the second syllable, expressed relatively to that in the first syllable. A higher value implies the use of a higher pitch range relative to syllable 1, and is particularly relevant for Tone 1’s examination. (Top-right) F0 movement calculated as the difference between the last and first 30-ms of the F0 pattern over the second syllable only. A negative value means a falling inflection, and is particularly relevant for Tone 4’s examination. (Bottom-left) F0 median for Tone 1 and (bottom-right) F0 movement for Tone 4, plotted across participants as a function of their chronological age.

FIGURE 7

F0 median for Tone 1 (left) and F0 movement for Tone 4 (right) plotted across participants as a function of their years of CI use. The CI participants who had used their CI for the longest time exhibited less modulation of their vocal chords either to differentiate the pitch range between syllables (as in the case of Tone 1) or to indicate the direction of a pitch sweep (as in the case of Tone 4).

FIGURE 8

Proportion of stimuli perceived as Tone 1 among a continuum of stimuli varying orthogonally in F0-variation, duration, and F0-height. A steeper slope of the psychometric function along a given dimension (e.g., F0 variation) reflects a stronger reliance on this cue.

FIGURE 9

Coefficients extracted from the logistic mixed-effect model reflecting the reliance on F0-variation (left) and duration (right) in the lexical tone recognition task, as a function of the children’s age.

FIGURE 10

Coefficients extracted from the logistic mixed-effect model reflecting the reliance on F0-variation (left) and duration (right) in the lexical tone recognition task, as a function of the F0 parameters extracted from production. Coefficients for F0 variation are expressed in log₁₀ of their absolute value to improve homogeneity of variance between the two participant groups.