Development of electrophysiological and behavioural measures of electrode discrimination in adult cochlear implant users

Publication date: Available online 4 July 2018
Source:Hearing Research
Author(s): Rajeev Mathew, Deborah Vickers, Patrick Boyle, Azhar Shaida, David Selvadurai, Dan Jiang, Jaime Undurraga
The plasticity of the auditory system enables it to adjust to electrical stimulation from cochlear implants (CI). Whilst speech perception may develop for many years after implant activation, very little is known about the changes in auditory processing that underpin these improvements. Such an understanding could help guide interventions that improve hearing performance. In this longitudinal study, we examine how electrode discrimination ability changes over time in newly implanted adult CI users. Electrode discrimination was measured with a behavioural task as well as the spatial auditory change complex (ACC), which is a cortical response to a change in place of stimulation. We show that there was significant improvement in electrode discrimination ability over time, though in certain individuals the process of accommodation was slower and more limited. We found a strong relationship between objective and behavioural measures of electrode discrimination using pass-fail rules. In several cases, the development of the spatial ACC preceded accurate behavioural discrimination. These data provide evidence for plasticity of auditory processing in adult CI users. Behavioural electrode discrimination score but not spatial ACC amplitude was found to be a significant predictor of speech perception. We suggest that it would be beneficial to measure electrode discrimination in CI users and that interventions that exploit the plastic capacity of the auditory system to improve basic auditory processing, could be used to optimize performance in CI users.



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Development of electrophysiological and behavioural measures of electrode discrimination in adult cochlear implant users

Publication date: Available online 4 July 2018
Source:Hearing Research
Author(s): Rajeev Mathew, Deborah Vickers, Patrick Boyle, Azhar Shaida, David Selvadurai, Dan Jiang, Jaime Undurraga
The plasticity of the auditory system enables it to adjust to electrical stimulation from cochlear implants (CI). Whilst speech perception may develop for many years after implant activation, very little is known about the changes in auditory processing that underpin these improvements. Such an understanding could help guide interventions that improve hearing performance. In this longitudinal study, we examine how electrode discrimination ability changes over time in newly implanted adult CI users. Electrode discrimination was measured with a behavioural task as well as the spatial auditory change complex (ACC), which is a cortical response to a change in place of stimulation. We show that there was significant improvement in electrode discrimination ability over time, though in certain individuals the process of accommodation was slower and more limited. We found a strong relationship between objective and behavioural measures of electrode discrimination using pass-fail rules. In several cases, the development of the spatial ACC preceded accurate behavioural discrimination. These data provide evidence for plasticity of auditory processing in adult CI users. Behavioural electrode discrimination score but not spatial ACC amplitude was found to be a significant predictor of speech perception. We suggest that it would be beneficial to measure electrode discrimination in CI users and that interventions that exploit the plastic capacity of the auditory system to improve basic auditory processing, could be used to optimize performance in CI users.



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Forward and Backward Masking of Consonants in School-Age Children and Adults

Purpose

This experiment sought to determine whether children's increased susceptibility to nonsimultaneous masking, particularly backward masking, is evident for speech stimuli.

Method

Five- to 9-year-olds and adults with normal hearing heard nonsense consonant–vowel–consonant targets. In Experiments 1 and 2, those targets were presented between two 250-ms segments of 70-dB-SPL speech-shaped noise, at either −30 dB signal-to-noise ratio (Experiment 1) or at the listener's word recognition threshold (Experiment 2). In Experiment 3, the target was presented in steady speech-shaped noise at listener threshold. For all experiments, percent correct was estimated for initial and final consonants.

Results

In the nonsimultaneous noise conditions, child–adult differences were larger for the final consonant than the initial consonant whether listeners were tested at −30 dB signal-to-noise ratio (Experiment 1) or at their individual word recognition threshold (Experiment 2). Children were not particularly susceptible to backward masking relative to adults when tested in a steady masker (Experiment 3).

Conclusions

Child–adult differences were greater for backward than forward masking for speech in a nonsimultaneous noise masker, as observed in previous psychophysical studies using tonal stimuli. Children's greater susceptibility to nonsimultaneous masking, and backward masking in particular, could play a role in their limited ability to benefit from masker envelope modulation when recognizing masked speech.

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Effects of Second Language Proficiency and Linguistic Uncertainty on Recognition of Speech in Native and Nonnative Competing Speech

Purpose

The purpose of this study was to investigate the effects of 2nd language proficiency and linguistic uncertainty on performance and listening effort in mixed language contexts.

Method

Thirteen native speakers of Dutch with varying degrees of fluency in English listened to and repeated sentences produced in both Dutch and English and presented in the presence of single-talker competing speech in both Dutch and English. Target and masker language combinations were presented in both blocked and mixed (unpredictable) conditions. In the blocked condition, in each block of trials the target–masker language combination remained constant, and the listeners were informed of both prior to beginning the block. In the mixed condition, target and masker language varied randomly from trial to trial. All listeners participated in all conditions. Performance was assessed in terms of speech reception thresholds, whereas listening effort was quantified in terms of pupil dilation.

Results

Performance (speech reception thresholds) and listening effort (pupil dilation) were both affected by 2nd language proficiency (English test score) and target and masker language: Performance was better in blocked as compared to mixed conditions, with Dutch as compared to English targets, and with English as compared to Dutch maskers. English proficiency was correlated with listening performance. Listeners also exhibited greater peak pupil dilation in mixed as compared to blocked conditions for trials with Dutch maskers, whereas pupil dilation during preparation for speaking was higher for English targets as compared to Dutch ones in almost all conditions.

Conclusions

Both listener's proficiency in a 2nd language and uncertainty about the target language on a given trial play a significant role in how bilingual listeners attend to speech in the presence of competing speech in different languages, but precise effects also depend on which language is serving as target and which as masker.

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Forward and Backward Masking of Consonants in School-Age Children and Adults

Purpose

This experiment sought to determine whether children's increased susceptibility to nonsimultaneous masking, particularly backward masking, is evident for speech stimuli.

Method

Five- to 9-year-olds and adults with normal hearing heard nonsense consonant–vowel–consonant targets. In Experiments 1 and 2, those targets were presented between two 250-ms segments of 70-dB-SPL speech-shaped noise, at either −30 dB signal-to-noise ratio (Experiment 1) or at the listener's word recognition threshold (Experiment 2). In Experiment 3, the target was presented in steady speech-shaped noise at listener threshold. For all experiments, percent correct was estimated for initial and final consonants.

Results

In the nonsimultaneous noise conditions, child–adult differences were larger for the final consonant than the initial consonant whether listeners were tested at −30 dB signal-to-noise ratio (Experiment 1) or at their individual word recognition threshold (Experiment 2). Children were not particularly susceptible to backward masking relative to adults when tested in a steady masker (Experiment 3).

Conclusions

Child–adult differences were greater for backward than forward masking for speech in a nonsimultaneous noise masker, as observed in previous psychophysical studies using tonal stimuli. Children's greater susceptibility to nonsimultaneous masking, and backward masking in particular, could play a role in their limited ability to benefit from masker envelope modulation when recognizing masked speech.

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Effects of Second Language Proficiency and Linguistic Uncertainty on Recognition of Speech in Native and Nonnative Competing Speech

Purpose

The purpose of this study was to investigate the effects of 2nd language proficiency and linguistic uncertainty on performance and listening effort in mixed language contexts.

Method

Thirteen native speakers of Dutch with varying degrees of fluency in English listened to and repeated sentences produced in both Dutch and English and presented in the presence of single-talker competing speech in both Dutch and English. Target and masker language combinations were presented in both blocked and mixed (unpredictable) conditions. In the blocked condition, in each block of trials the target–masker language combination remained constant, and the listeners were informed of both prior to beginning the block. In the mixed condition, target and masker language varied randomly from trial to trial. All listeners participated in all conditions. Performance was assessed in terms of speech reception thresholds, whereas listening effort was quantified in terms of pupil dilation.

Results

Performance (speech reception thresholds) and listening effort (pupil dilation) were both affected by 2nd language proficiency (English test score) and target and masker language: Performance was better in blocked as compared to mixed conditions, with Dutch as compared to English targets, and with English as compared to Dutch maskers. English proficiency was correlated with listening performance. Listeners also exhibited greater peak pupil dilation in mixed as compared to blocked conditions for trials with Dutch maskers, whereas pupil dilation during preparation for speaking was higher for English targets as compared to Dutch ones in almost all conditions.

Conclusions

Both listener's proficiency in a 2nd language and uncertainty about the target language on a given trial play a significant role in how bilingual listeners attend to speech in the presence of competing speech in different languages, but precise effects also depend on which language is serving as target and which as masker.

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Audiology Faculty Author Impact Metrics as a Function of Institution

Purpose

The purpose of this study was to develop a method for the assessment of audiology author impact as a function of institution and compare these results to a recent college ranking of audiology graduate programs.

Method

Scopus author impact metrics (i.e., number of documents, number of citations, and h index) from a previous study (Stuart, Faucette, & Thomas, 2017) were generated for 79 accredited graduate programs in audiology in the United States and Canada. Author impact metrics were summed to represent the total institution output, and median values were calculated to reflect a measure of central tendency of individual faculty performance.

Results

Three hundred and seventy-nine audiology faculty members were identified and of those 86.0% (n = 326) were found in Scopus. Database presence increased with increasing rank (p = .003). Scopus index values were positively skewed. The total summed number of documents, citations, and h indices were positively correlated with the total number of faculty in the institutions and with the summed number of coauthors (p < .001). The median number of documents, citations, and h indices were not significantly correlated with the total number of faculty in the institutions but were positively correlated with the median number of coauthors (p < .001). In general, indices were higher for research/doctoral versus nonresearch universities. Higher college program rankings were statistically related with better Scopus index values.

Conclusion

These institutional metrics may be used to serve as a benchmark for institutional production, attracting students, hiring faculty, and assessing allocation of institutional funding.

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