Relative Contributions of Spectral and Temporal Cues for Speech Recognition in Patients with Sensorineural Hearing Loss

Auditory discrimination in aging bilinguals vs. monolinguals with and without hearing loss

Demands for effective assessments of speech perception specific to the aging brain are increasing, as the impacts of hearing loss on an individual's functional health, socialization, and cognition have become more widely recognized. Understanding the mechanisms behind the optimal function of the aging brain in relation to speech and language is challenging, especially in the bilingual population where the language learning and language interference processes could be mistaken for perceptual difficulty. Age-related presbycusis is unavoidable, and the contributions of this sensorineural hearing loss (SNHL) process on impaired speech recognition are not completely understood. This lack of understanding of the effects of aging and bilingual language competency on speech perception can act as a barrier to successful auditory rehabilitation. The present study investigated the effects of aging on vowel sound discrimination in adult listeners (age 50+) with the following characteristics: American English (AE) monolinguals with normal hearing, simultaneous or early sequential Spanish-English (SE) bilinguals with normal hearing, and AE monolinguals with SNHL (AE-SNHL). The goal was to identify the differences in vowel sound discrimination performance between the monolingual and bilingual aging populations to guide future language assessments and intervention processes. English vowel discrimination was assessed using an AXB discrimination task in quiet and using the Quick Speech in Noise (QuickSIN) test. SE bilinguals were outperformed by AE and AE-SNHL monolinguals, suggesting SE bilinguals primarily use their L1 acoustic properties to discriminate speech segments. No significant difference was found in QuickSIN performance between the bilingual and the monolingual groups, but there was a significant difference between AE and AE-SNHL. In conclusion, vowel discrimination was affected by interference with the native language, while performance in the noise condition was affected by hearing loss. The results of this study contribute to our understanding of the age-related speech processing deficits from three different aging groups regarding the cognitive control system.

Relative contributions of temporal envelope and fine structure cues to lexical tone recognition in hearing-impaired listeners

It has been reported that normal-hearing Chinese speakers base their lexical tone recognition on fine structure regardless of temporal envelope cues. However, a few psychoacoustic and perceptual studies have demonstrated that listeners with sensorineural hearing impairment may have an impaired ability to use fine structure information, whereas their ability to use temporal envelope information is close to normal. The purpose of this study is to investigate the relative contributions of temporal envelope and fine structure cues to lexical tone recognition in normal-hearing and hearing-impaired native Mandarin Chinese speakers. Twenty-two normal-hearing subjects and 31 subjects with various degrees of sensorineural hearing loss participated in the study. Sixteen sets of Mandarin monosyllables with four tone patterns for each were processed through a "chimeric synthesizer" in which temporal envelope from a monosyllabic word of one tone was paired with fine structure from the same monosyllable of other tones. The chimeric tokens were generated in the three channel conditions (4, 8, and 16 channels). Results showed that differences in tone responses among the three channel conditions were minor. On average, 90.9%, 70.9%, 57.5%, and 38.2% of tone responses were consistent with fine structure for normal-hearing, moderate, moderate to severe, and severely hearing-impaired groups respectively, whereas 6.8%, 21.1%, 31.4%, and 44.7% of tone responses were consistent with temporal envelope cues for the above-mentioned groups. Tone responses that were consistent neither with temporal envelope nor fine structure had averages of 2.3%, 8.0%, 11.1%, and 17.1% for the above-mentioned groups of subjects. Pure-tone average thresholds were negatively correlated with tone responses that were consistent with fine structure, but were positively correlated with tone responses that were based on the temporal envelope cues. Consistent with the idea that the spectral resolvability is responsible for fine structure coding, these results demonstrated that, as hearing loss becomes more severe, lexical tone recognition relies increasingly on temporal envelope rather than fine structure cues due to the widened auditory filters.

Contribution of spectral cues to mandarin lexical tone recognition in normal-hearing and hearing-impaired Mandarin Chinese speakers

OBJECTIVE

The purpose of this study was to investigate the contribution of spectral fine structure and spectral envelope cues to recognition of Mandarin lexical tones in normal-hearing and sensorineural hearing-impaired Mandarin-speaking listeners.

DESIGN

Four groups of subjects participated in the study, including 20 normal-hearing, 20 moderately, 20 moderately to severely, and 8 severely hearing-impaired listeners. The original speech materials consisted of 16 sets of Mandarin monosyllables spoken by a male and a female. Each monosyllable had four tonal patterns, resulting in a total of 64 combinations of consonants, vowels, and tones. A Linear Predictive Coding (LPC) algorithm was used to create two sets of synthesized materials, including 128 tokens with the original spectral fine structure mixed with the spectral envelope from a different tone, as well as 128 tokens with noise fine structure and the original spectral envelope. All subjects participated in tone recognition tests using the two sets of chimeric tone tokens. Oral responses to tones were recorded and scored as percent correct.

RESULTS

Hearing-impaired listeners could take advantage of spectral fine structure in the recognition of lexical tones, but with increasing hearing loss, the ability of hearing-impaired listeners to recognize tones became worse, especially for severely hearing-impaired listeners. Hearing-impaired listeners showed significant differences in tone recognition between the male and female voices. Tone 3 was the easiest tone to perceive, followed by tone 2, whereas tones 1 and 4 were hard for all subjects, particularly when only the spectral envelope cue was available. Hearing-impaired listeners showed a significantly lower level of lexical tone recognition than normal-hearing listeners when using spectral envelope cues in comparison with normal-hearing listeners.

CONCLUSIONS

These results demonstrate that the spectral fine structure cue dominates lexical tone recognition for all subjects. Listeners with sensorineural hearing impairment showed reduced ability in the recognition of lexical tones using both spectral fine structure and spectral envelope cues, which may result from their impaired auditory spectral resolution.