Talker variability in word recognition under cochlear implant simulation: Does talker gender matter?

Evaluating Listening Effort in Unilateral, Bimodal, and Bilateral Cochlear Implant Users

OBJECTIVE

Evaluate listening effort (LE) in unilateral, bilateral, and bimodal cochlear implant (CI) users. Establish an easy-to-implement task of LE that could be useful for clinical decision making.

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary neurotology center.

METHODS

The Sentence Final Word Identification and Recall Task, an established measure of LE, was modified to include challenging listening conditions (multitalker babble, gender, and emotional variation; test), in addition to single-talker sentences (control). Participants listened to lists of sentences in each condition and recalled the last word of each sentence. LE was quantified by percentage of words correctly recalled and was compared across conditions, across CI groups, and within subjects (best aided vs monaural).

RESULTS

A total of 24 adults between the ages of 37 and 82 years enrolled, including 4 unilateral CI users (CI), 10 bilateral CI users (CICI), and 10 bimodal CI users (CIHA). Task condition impacted LE (P < .001), but hearing configuration and listener group did not (P = .90). Working memory capacity and contralateral hearing contributed to individual performance.

CONCLUSION

This study adds to the growing body of literature on LE in challenging listening conditions for CI users and demonstrates feasibility of a simple behavioral task that could be implemented clinically to assess LE. This study also highlights the potential benefits of bimodal hearing and individual hearing and cognitive factors in understanding individual differences in performance, which will be evaluated through further research.

Development of a Sentence Verification Task to Measure Speech Comprehension and Listening Effort in Cochlear Implant Users

PURPOSE

Tests measuring speech comprehension and listening effort for cochlear implant (CI) users may reflect important aspects of real-world speech communication. In this study, we describe the development of a multiple-talker, English-language sentence verification task (SVT) for use in adult CI users to measure speech comprehension and listening effort. We also examine whether talker differences affect speech comprehension and listening effort.

METHOD

Thirteen experienced adult CI users participated in the study and underwent testing using a newly developed multiple-talker SVT. Participants were sequentially presented with audio recordings of unique sentences spoken in English by six different talkers. Participants classified each sentence as either true or false. Accuracy of classification and the response time (RT) for correct responses were used as measures of comprehension and listening effort, respectively. The effect of talker on the results was further analyzed.

RESULTS

All 13 participants successfully completed the SVT. The mean verification accuracy for participants was 87.2% ± 8.8%. The mean RT for correct responses across participants was 1,050 ms ± 391 ms. When stratified by talker, verification accuracy ranged from 83.7% to 95.2% and mean RTs across participant ranged from 786 ms to 1,254 ms. Talker did not have a significant effect on sentence classification accuracy, but it did have a significant effect on RTs (p < .001).

CONCLUSIONS

The SVT is an easily implemented test that can assess speech comprehension and listening effort simultaneously. CI users may experience increased effort for comprehending certain talkers' speech, despite showing similar levels of comprehension accuracy.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24126630.

Assessment of High-Variability Speech Recognition in Adult Cochlear Implant Users using PRESTO

BACKGROUND

 Speech recognition in adult cochlear implant (CI) users is typically assessed using sentence materials with low talker variability. Little is known about the effects of talker variability on speech recognition in adult CI users, the factors underlying individual differences in speech recognition with high talker variability, or how sentence materials with high talker variability could be utilized clinically.

PURPOSE

 To examine the effects of talker variability on sentence recognition in adult CI users, using sentences from the Perceptually Robust English Sentence Test Open-Set (PRESTO), and to examine the relation between working memory capacity and high-variability speech recognition.

RESEARCH DESIGN

 Postlingually deafened adult CI users and adults with self-reported normal hearing (NH) under CI simulation completed sentence recognition tests that contained varying levels of talker variability, including Hearing in Noise Test (HINT; low-variability), AzBio (moderate-variability), and PRESTO sentences (high-variability). The tasks were completed in both quiet and multitalker babble (MTB). For the adult CI users only, the relation between sentence recognition accuracy and working memory capacity was assessed.

STUDY SAMPLE

 Twenty postlingually deafened adult CI users and 35 NH adults under 8-channel acoustic noise-vocoder simulations of CI hearing.

RESULTS

 In both CI and NH groups, performance decreased as a function of increased talker variability, with the best scores obtained on HINT (low-variability), then AzBio (moderate-variability), followed by PRESTO (high-variability) in quiet. In MTB, performance was significantly lower on PRESTO sentences, compared with HINT and AzBio sentences, which were not significantly different. Working memory capacity in the CI users was related to sentence recognition accuracy across all materials and conditions.

CONCLUSION

 Findings from the current study suggest that the increased talker variability in the PRESTO sentence materials has a detrimental effect on speech recognition in both adult CI users and NH listeners under CI simulation, particularly when speech is further degraded by MTB. For adult CI users, working memory capacity contributes to speech recognition abilities. Sentence recognition testing with high-variability, multitalker materials, as in PRESTO, provides robust assessment of speech recognition abilities for research and clinical application, generating a wide range of scores for evaluating individual differences without ceiling effects when compared with conventional low-variability sentences.

Factors affecting talker discrimination ability in adult cochlear implant users

INTRODUCTION

Real-world speech communication involves interacting with many talkers with diverse voices and accents. Many adults with cochlear implants (CIs) demonstrate poor talker discrimination, which may contribute to real-world communication difficulties. However, the factors contributing to talker discrimination ability, and how discrimination ability relates to speech recognition outcomes in adult CI users are still unknown. The current study investigated talker discrimination ability in adult CI users, and the contributions of age, auditory sensitivity, and neurocognitive skills. In addition, the relation between talker discrimination ability and multiple-talker sentence recognition was explored.

METHODS

Fourteen post-lingually deaf adult CI users (3 female, 11 male) with ≥1 year of CI use completed a talker discrimination task. Participants listened to two monosyllabic English words, produced by the same talker or by two different talkers, and indicated if the words were produced by the same or different talkers. Nine female and nine male native English talkers were paired, resulting in same- and different-talker pairs as well as same-gender and mixed-gender pairs. Participants also completed measures of spectro-temporal processing, neurocognitive skills, and multiple-talker sentence recognition.

RESULTS

CI users showed poor same-gender talker discrimination, but relatively good mixed-gender talker discrimination. Older age and weaker neurocognitive skills, in particular inhibitory control, were associated with less accurate mixed-gender talker discrimination. Same-gender discrimination was significantly related to multiple-talker sentence recognition accuracy.

CONCLUSION

Adult CI users demonstrate overall poor talker discrimination ability. Individual differences in mixed-gender discrimination ability were related to age and neurocognitive skills, suggesting that these factors contribute to the ability to make use of available, degraded talker characteristics. Same-gender talker discrimination was associated with multiple-talker sentence recognition, suggesting that access to subtle talker-specific cues may be important for speech recognition in challenging listening conditions.

Effects of Spectral Envelope and Fundamental Frequency Shifts on the Perception of Foreign-Accented Speech

To investigate the role of spectral pattern information in the perception of foreign-accented speech, we measured the effects of spectral shifts on judgments of talker discrimination, perceived naturalness, and intelligibility when listening to Mandarin-accented English and native-accented English sentences. In separate conditions, the spectral envelope and fundamental frequency (F0) contours were shifted up or down in three steps using coordinated scale factors (multiples of 8% and 30%, respectively). Experiment 1 showed that listeners perceive spectrally shifted sentences as coming from a different talker for both native-accented and foreign-accented speech. Experiment 2 demonstrated that downward shifts applied to male talkers and the largest upward shifts applied to all talkers reduced the perceived naturalness, regardless of accent. Overall, listeners rated foreign-accented speech as sounding less natural even for unshifted speech. In Experiment 3, introducing spectral shifts further lowered the intelligibility of foreign-accented speech. When speech from the same foreign-accented talker was shifted to simulate five different talkers, increased exposure failed to produce an improvement in intelligibility scores, similar to the pattern observed when listeners actually heard five foreign-accented talkers. Intelligibility of spectrally shifted native-accented speech was near ceiling performance initially, and no further improvement or decrement was observed. These experiments suggest a mechanism that utilizes spectral envelope and F0 cues in a talker-dependent manner to support the perception of foreign-accented speech.

Lexical Effects on the Perceived Clarity of Noise-Vocoded Speech in Younger and Older Listeners

When listening to degraded speech, such as speech delivered by a cochlear implant (CI), listeners make use of top-down linguistic knowledge to facilitate speech recognition. Lexical knowledge supports speech recognition and enhances the perceived clarity of speech. Yet, the extent to which lexical knowledge can be used to effectively compensate for degraded input may depend on the degree of degradation and the listener's age. The current study investigated lexical effects in the compensation for speech that was degraded via noise-vocoding in younger and older listeners. In an online experiment, younger and older normal-hearing (NH) listeners rated the clarity of noise-vocoded sentences on a scale from 1 ("very unclear") to 7 ("completely clear"). Lexical information was provided by matching text primes and the lexical content of the target utterance. Half of the sentences were preceded by a matching text prime, while half were preceded by a non-matching prime. Each sentence also consisted of three key words of high or low lexical frequency and neighborhood density. Sentences were processed to simulate CI hearing, using an eight-channel noise vocoder with varying filter slopes. Results showed that lexical information impacted the perceived clarity of noise-vocoded speech. Noise-vocoded speech was perceived as clearer when preceded by a matching prime, and when sentences included key words with high lexical frequency and low neighborhood density. However, the strength of the lexical effects depended on the level of degradation. Matching text primes had a greater impact for speech with poorer spectral resolution, but lexical content had a smaller impact for speech with poorer spectral resolution. Finally, lexical information appeared to benefit both younger and older listeners. Findings demonstrate that lexical knowledge can be employed by younger and older listeners in cognitive compensation during the processing of noise-vocoded speech. However, lexical content may not be as reliable when the signal is highly degraded. Clinical implications are that for adult CI users, lexical knowledge might be used to compensate for the degraded speech signal, regardless of age, but some CI users may be hindered by a relatively poor signal.

Talker Adaptation and Lexical Difficulty Impact Word Recognition in Adults with Cochlear Implants

INTRODUCTION

Talker-specific adaptation facilitates speech recognition in normal-hearing listeners. This study examined talker adaptation in adult cochlear implant (CI) users. Three hypotheses were tested: (1) high-performing adult CI users show improved word recognition following exposure to a talker ("talker adaptation"), particularly for lexically hard words, (2) individual performance is determined by auditory sensitivity and neurocognitive skills, and (3) individual performance relates to real-world functioning.

METHODS

Fifteen high-performing, post-lingually deaf adult CI users completed a word recognition task consisting of 6 single-talker blocks (3 female/3 male native English speakers); words were lexically "easy" and "hard." Recognition accuracy was assessed "early" and "late" (first vs. last 10 trials); adaptation was assessed as the difference between late and early accuracy. Participants also completed measures of spectral-temporal processing and neurocognitive skills, as well as real-world measures of multiple-talker sentence recognition and quality of life (QoL).

RESULTS

CI users showed limited talker adaptation overall, but performance improved for lexically hard words. Stronger spectral-temporal processing and neurocognitive skills were weakly to moderately associated with more accurate word recognition and greater talker adaptation for hard words. Finally, word recognition accuracy for hard words was moderately related to multiple-talker sentence recognition and QoL.

CONCLUSION

Findings demonstrate a limited talker adaptation benefit for recognition of hard words in adult CI users. Both auditory sensitivity and neurocognitive skills contribute to performance, suggesting additional benefit from adaptation for individuals with stronger skills. Finally, processing differences related to talker adaptation and lexical difficulty may be relevant to real-world functioning.