Contributions of lexical tone to Mandarin sentence recognition in hearing-impaired listeners under noisy conditions

Lexical tone recognition in multi-talker babbles and steady-state noise by Mandarin-speaking children with unilateral cochlear implants or bimodal hearing

BACKGROUND AND OBJECTIVES

Lexical tone presents challenges to cochlear implant (CI) users especially in noise conditions. Bimodal hearing utilizes residual acoustic hearing in the contralateral side and may offer benefits for tone recognition in noise. The purpose of the present study was to evaluate tone recognition in both steady-state noise and multi-talker babbles by the prelingually-deafened, Mandarin-speaking children with unilateral CIs or bimodal hearing.

METHODS

Fifty-three prelingually-deafened, Mandarin-speaking children who received CIs participated in this study. Twenty-two of them were unilateral CI users and 31 wore a hearing aid (HA) in the contralateral ear (i.e., bimodal hearing). All subjects were tested for Mandarin tone recognition in quiet and in two types of maskers: speech-spectrum-shaped noise (SSN) and two-talker babbles (TTB) at four signal-to-noise ratios (-6, 0, +6, and +12 dB).

RESULTS

While no differences existed in tone recognition in quiet between the two groups, the Bimodal group outperformed the Unilateral CI group under noise conditions. The differences between the two groups were significant at SNRs of 0, +6, and +12 dB in the SSN conditions (all p < 0.05), and at SNRs of +6 and +12 dB of TTB conditions (both p < 0.01), but not significant at other conditions (p > 0.05). The TTB exerted a greater masking effect than the SSN for tone recognition in the Unilateral CI group as well as in the Bimodal group at all SNRs tested (all p < 0.05). Among demographic or audiometric variables, only age at implantation showed a weak but significant correlation with the mean tone recognition performance under the SSN conditions (r = -0.276, p = 0.045). However, when Bonferroni correction was applied to the correlation analysis results, the weak correlation became not significant.

CONCLUSION

Prelingually-deafened children with CIs face challenges in tone perception in noisy environments, especially when the noise is fluctuating in amplitude such as the multi-talker babbles. Wearing a HA on the contralateral side when residual hearing permits is beneficial for tone recognition in noise.

Brain hemispheres with right temporal lobe damage swap dominance in early auditory processing of lexical tones

Labor division of the two brain hemispheres refers to the dominant processing of input information on one side of the brain. At an early stage, or a preattentive stage, the right brain hemisphere is shown to dominate the auditory processing of tones, including lexical tones. However, little is known about the influence of brain damage on the labor division of the brain hemispheres for the auditory processing of linguistic tones. Here, we demonstrate swapped dominance of brain hemispheres at the preattentive stage of auditory processing of Chinese lexical tones after a stroke in the right temporal lobe (RTL). In this study, we frequently presented lexical tones to a group of patients with a stroke in the RTL and infrequently varied the tones to create an auditory contrast. The contrast evoked a mismatch negativity response, which indexes auditory processing at the preattentive stage. In the participants with a stroke in the RTL, the mismatch negativity response was lateralized to the left side, in contrast to the right lateralization pattern in the control participants. The swapped dominance of brain hemispheres indicates that the RTL is a core area for early-stage auditory tonal processing. Our study indicates the necessity of rehabilitating tonal processing functions for tonal language speakers who suffer an RTL injury.

Differential weighting of temporal envelope cues from the low-frequency region for Mandarin sentence recognition in noise

BACKGROUND

Temporal envelope cues are conveyed by cochlear implants (CIs) to hearing loss patients to restore hearing. Although CIs could enable users to communicate in clear listening environments, noisy environments still pose a problem. To improve speech-processing strategies used in Chinese CIs, we explored the relative contributions made by the temporal envelope in various frequency regions, as relevant to Mandarin sentence recognition in noise.

METHODS

Original speech material from the Mandarin version of the Hearing in Noise Test (MHINT) was mixed with speech-shaped noise (SSN), sinusoidally amplitude-modulated speech-shaped noise (SAM SSN), and sinusoidally amplitude-modulated (SAM) white noise (4 Hz) at a + 5 dB signal-to-noise ratio, respectively. Envelope information of the noise-corrupted speech material was extracted from 30 contiguous bands that were allocated to five frequency regions. The intelligibility of the noise-corrupted speech material (temporal cues from one or two regions were removed) was measured to estimate the relative weights of temporal envelope cues from the five frequency regions.

RESULTS

In SSN, the mean weights of Regions 1-5 were 0.34, 0.19, 0.20, 0.16, and 0.11, respectively; in SAM SSN, the mean weights of Regions 1-5 were 0.34, 0.17, 0.24, 0.14, and 0.11, respectively; and in SAM white noise, the mean weights of Regions 1-5 were 0.46, 0.24, 0.22, 0.06, and 0.02, respectively.

CONCLUSIONS

The results suggest that the temporal envelope in the low-frequency region transmits the greatest amount of information in terms of Mandarin sentence recognition for three types of noise, which differed from the perception strategy employed in clear listening environments.

Aging Effect on Mandarin Chinese Vowel and Tone Identification in Six-Talker Babble

Purpose The purpose of this study was to measure Mandarin Chinese vowel-plus-tone identification in quiet and noise for younger and older listeners. Method Two types of noise served as the masker, namely, six-talker babble and babble-modulated noise, at two signal-to-noise ratios (SNRs) of -4 and -8 dB. Fourteen listeners from both age groups were recruited, and three sets of data analyses were conducted: the identification of vowel plus tone, the identification of vowel, and the identification of tone. Results Younger listeners outperformed older listeners in all listening conditions, whereas the younger-older listener difference became greater in noise than in quiet, indicating a more detrimental effect of noise for older listeners than for younger listeners. In addition, vowel identification showed slightly better scores than tone identification in noise, suggesting that noise appeared to affect tone perception more negatively than vowel perception in Mandarin Chinese. At -4 dB SNR, there was a significantly greater amount of informational masking (IM) and a greater amount of energetic masking (EM) for older listeners than for younger listeners. At -8 dB SNR, there was a greater amount of EM for older listeners than for younger listeners but with no group difference in the amount of IM. Conclusion These results suggest that older listeners received a more negative impact of noise for Mandarin Chinese phonemic and tone recognition and had a larger amount of IM or EM from competing speech noise than younger listeners, depending on the SNR.

Speech perception in noise: Masking and unmasking

Speech perception is essential for daily communication. Background noise or concurrent talkers, on the other hand, can make it challenging for listeners to track the target speech (i.e., cocktail party problem). The present study reviews and compares existing findings on speech perception and unmasking in cocktail party listening environments in English and Mandarin Chinese. The review starts with an introduction section followed by related concepts of auditory masking. The next two sections review factors that release speech perception from masking in English and Mandarin Chinese, respectively. The last section presents an overall summary of the findings with comparisons between the two languages. Future research directions with respect to the difference in literature on the reviewed topic between the two languages are also discussed.