Voice fundamental frequency differences and speech recognition with noise and speech maskers in cochlear implant recipients

The Relationship Between Speech Discrimination in Noise and Spectral Resolution, Temporal Resolution, and Melodic Contour Identification Abilities in Cochlear Implant Users

PURPOSE

Speech-in-noise performance of cochlear implant (CI) users varies considerably, and understanding speech in a complex auditory environment remains challenging. It is still unclear which auditory skill is causing this difficulty. This study aimed to evaluate spectral resolution, temporal resolution, and melodic contour identification (MCI) skills to determine which of these skills is most closely related to speech understanding in noise and to investigate whether these three skills differ among CI users with varying performances in speech-in-noise tasks.

METHOD

The three-syllable word identification test (in quiet), the Turkish Matrix Test (in quiet, at fixed +8 dB SNR, and adaptively in noise) were administered to evaluate speech perception to 24 adult CI users (18-55 years old). To evaluate auditory abilities, tests involving spectral-temporally modulated ripple, gap detection, and MCI were administered. CI recipients were separated into two groups (good and low performers) based on their adaptive matrix speech reception threshold (SRT) in noise.

RESULTS

The abilities of temporal and spectral resolution were correlated with speech understanding at +8 dB SNR. However, the effect of spectral resolution on understanding at +8 dB SN was not significant. The skill most associated with the Matrix SRT in noise was spectral resolution. The groups differed significantly in both the speech tests and spectral resolution skills.

CONCLUSIONS

Varying spectral resolution skills among CI users may affect their speech perception performance in noise. The effects of spectral and temporal resolution on speech perception in noise varied across noise conditions. Thus, there may be an increased requirement for spectral resolution in more adverse listening environments.

Assessment of Speech Processing and Listening Effort Associated With Speech-on-Speech Masking Using the Visual World Paradigm and Pupillometry

Speech-on-speech masking is a common and challenging situation in everyday verbal communication. The ability to segregate competing auditory streams is a necessary requirement for focusing attention on the target speech. The Visual World Paradigm (VWP) provides insight into speech processing by capturing gaze fixations on visually presented icons that reflect the speech signal. This study aimed to propose a new VWP to examine the time course of speech segregation when competing sentences are presented and to collect pupil size data as a measure of listening effort. Twelve young normal-hearing participants were presented with competing matrix sentences (structure "name-verb-numeral-adjective-object") diotically via headphones at four target-to-masker ratios (TMRs), corresponding to intermediate to near perfect speech recognition. The VWP visually presented the number and object words from both the target and masker sentences. Participants were instructed to gaze at the corresponding words of the target sentence without providing verbal responses. The gaze fixations consistently reflected the different TMRs for both number and object words. The slopes of the fixation curves were steeper, and the proportion of target fixations increased with higher TMRs, suggesting more efficient segregation under more favorable conditions. Temporal analysis of pupil data using Bayesian paired sample t-tests showed a corresponding reduction in pupil dilation with increasing TMR, indicating reduced listening effort. The results support the conclusion that the proposed VWP and the captured eye movements and pupil dilation are suitable for objective assessment of sentence-based speech-on-speech segregation and the corresponding listening effort.

Perception of voice cues and speech-in-speech by children with prelingual single-sided deafness and a cochlear implant

Voice cues, such as fundamental frequency (F0) and vocal tract length (VTL), help listeners identify the speaker's gender, perceive the linguistic and emotional prosody, and segregate competing talkers. Postlingually implanted adult cochlear implant (CI) users seem to have difficulty in perceiving and making use of voice cues, especially of VTL. Early implanted child CI users, in contrast, perceive and make use of both voice cues better than CI adults, and in patterns similar to their peers with normal hearing (NH). In our study, we investigated the perception and use of voice cues in children with single-sided deafness (SSD) who received their CI at an early age (SSD+CI), in an attempt to bridge the gap between these two groups. The SSD+CI children have access to bilateral auditory information and often receive their CI at an early age, similar to CI children. They may also have dominant acoustic representations, similar to CI adults who acquired hearing loss at a later age. As such, the current study aimed to investigate the perception and use of voice cues by a group of nine early-implanted children with prelingual SSD. The study consisted of three experiments: F0 and VTL discrimination, voice gender categorization, and speech-in-speech perception. In each experiment, the results of the SSD group are compared to children and adults with CIs (for their CI ear) and with typical hearing (for their NH ear). Overall, the SSD+CI children had poorer VTL detection thresholds with their CI compared to their NH ear, while their F0 perception was similar across ears. Detection thresholds for both F0 and VTL with their CI ear was comparable to those of bilaterally implanted CI children, suggesting that SSD+CI children do not only rely on their NH ear, but actually make use of their CI. SSD+CI children relied more heavily on F0 cues than on VTL cues for voice gender categorization, with cue weighting patterns comparable to those of CI adults. In contrast to CI children, the SSD+CI children showed limited speech perception benefit based on F0 and VTL differences between the target and masker speaker, which again corresponded to the results of CI adults. Altogether, the SSD+CI children make good use of their CI, despite a good-hearing ear, however, the perceptual patterns seem to fall in-between those of CI children and CI adults. Perhaps a combination of childhood neuroplasticity, limited experience with relying only on the CI, and a dominant acoustic representation of voice gender explain these results.

Prelingually Deaf Children With Cochlear Implants Show Better Perception of Voice Cues and Speech in Competing Speech Than Postlingually Deaf Adults With Cochlear Implants

OBJECTIVES

Postlingually deaf adults with cochlear implants (CIs) have difficulties with perceiving differences in speakers' voice characteristics and benefit little from voice differences for the perception of speech in competing speech. However, not much is known yet about the perception and use of voice characteristics in prelingually deaf implanted children with CIs. Unlike CI adults, most CI children became deaf during the acquisition of language. Extensive neuroplastic changes during childhood could make CI children better at using the available acoustic cues than CI adults, or the lack of exposure to a normal acoustic speech signal could make it more difficult for them to learn which acoustic cues they should attend to. This study aimed to examine to what degree CI children can perceive voice cues and benefit from voice differences for perceiving speech in competing speech, comparing their abilities to those of normal-hearing (NH) children and CI adults.

DESIGN

CI children's voice cue discrimination (experiment 1), voice gender categorization (experiment 2), and benefit from target-masker voice differences for perceiving speech in competing speech (experiment 3) were examined in three experiments. The main focus was on the perception of mean fundamental frequency (F0) and vocal-tract length (VTL), the primary acoustic cues related to speakers' anatomy and perceived voice characteristics, such as voice gender.

RESULTS

CI children's F0 and VTL discrimination thresholds indicated lower sensitivity to differences compared with their NH-age-equivalent peers, but their mean discrimination thresholds of 5.92 semitones (st) for F0 and 4.10 st for VTL indicated higher sensitivity than postlingually deaf CI adults with mean thresholds of 9.19 st for F0 and 7.19 st for VTL. Furthermore, CI children's perceptual weighting of F0 and VTL cues for voice gender categorization closely resembled that of their NH-age-equivalent peers, in contrast with CI adults. Finally, CI children had more difficulties in perceiving speech in competing speech than their NH-age-equivalent peers, but they performed better than CI adults. Unlike CI adults, CI children showed a benefit from target-masker voice differences in F0 and VTL, similar to NH children.

CONCLUSION

Although CI children's F0 and VTL voice discrimination scores were overall lower than those of NH children, their weighting of F0 and VTL cues for voice gender categorization and their benefit from target-masker differences in F0 and VTL resembled that of NH children. Together, these results suggest that prelingually deaf implanted CI children can effectively utilize spectrotemporally degraded F0 and VTL cues for voice and speech perception, generally outperforming postlingually deaf CI adults in comparable tasks. These findings underscore the presence of F0 and VTL cues in the CI signal to a certain degree and suggest other factors contributing to the perception challenges faced by CI adults.

Preclinical evaluation of the efficacy and safety of AAV1-hOTOF in mice and nonhuman primates

Pathogenic mutations in the OTOF gene cause autosomal recessive hearing loss (DFNB9), one of the most common forms of auditory neuropathy. There is no biological treatment for DFNB9. Here, we designed an OTOF gene therapy agent by dual-adeno-associated virus 1 (AAV1) carrying human OTOF coding sequences with the expression driven by the hair cell-specific promoter Myo15, AAV1-hOTOF. To develop a clinical application of AAV1-hOTOF gene therapy, we evaluated its efficacy and safety in animal models using pharmacodynamics, behavior, and histopathology. AAV1-hOTOF inner ear delivery significantly improved hearing in Otof-/- mice without affecting normal hearing in wild-type mice. AAV1 was predominately distributed to the cochlea, although it was detected in other organs such as the CNS and the liver, and no obvious toxic effects of AAV1-hOTOF were observed in mice. To further evaluate the safety of Myo15 promoter-driven AAV1-transgene, AAV1-GFP was delivered into the inner ear of Macaca fascicularis via the round window membrane. AAV1-GFP transduced 60%-94% of the inner hair cells along the cochlear turns. AAV1-GFP was detected in isolated organs and no significant adverse effects were detected. These results suggest that AAV1-hOTOF is well tolerated and effective in animals, providing critical support for its clinical translation.

Differential Effects of Binaural Pitch Fusion Range on the Benefits of Voice Gender Differences in a "Cocktail Party" Environment for Bimodal and Bilateral Cochlear Implant Users

OBJECTIVES

Some cochlear implant (CI) users are fitted with a CI in each ear ("bilateral"), while others have a CI in one ear and a hearing aid in the other ("bimodal"). Presently, evaluation of the benefits of bilateral or bimodal CI fitting does not take into account the integration of frequency information across the ears. This study tests the hypothesis that CI listeners, especially bimodal CI users, with a more precise integration of frequency information across ears ("sharp binaural pitch fusion") will derive greater benefit from voice gender differences in a multi-talker listening environment.

DESIGN

Twelve bimodal CI users and twelve bilateral CI users participated. First, binaural pitch fusion ranges were measured using the simultaneous, dichotic presentation of reference and comparison stimuli (electric pulse trains for CI ears and acoustic tones for HA ears) in opposite ears, with reference stimuli fixed and comparison stimuli varied in frequency/electrode to find the range perceived as a single sound. Direct electrical stimulation was used in implanted ears through the research interface, which allowed selective stimulation of one electrode at a time, and acoustic stimulation was used in the non-implanted ears through the headphone. Second, speech-on-speech masking performance was measured to estimate masking release by voice gender difference between target and maskers (VGRM). The VGRM was calculated as the difference in speech recognition thresholds of target sounds in the presence of same-gender or different-gender maskers.

RESULTS

Voice gender differences between target and masker talkers improved speech recognition performance for the bimodal CI group, but not the bilateral CI group. The bimodal CI users who benefited the most from voice gender differences were those who had the narrowest range of acoustic frequencies that fused into a single sound with stimulation from a single electrode from the CI in the opposite ear. There was no similar voice gender difference benefit of narrow binaural fusion range for the bilateral CI users.

CONCLUSIONS

The findings suggest that broad binaural fusion reduces the acoustical information available for differentiating individual talkers in bimodal CI users, but not for bilateral CI users. In addition, for bimodal CI users with narrow binaural fusion who benefit from voice gender differences, bilateral implantation could lead to a loss of that benefit and impair their ability to selectively attend to one talker in the presence of multiple competing talkers. The results suggest that binaural pitch fusion, along with an assessment of residual hearing and other factors, could be important for assessing bimodal and bilateral CI users.

Parameter-Specific Morphing Reveals Contributions of Timbre to the Perception of Vocal Emotions in Cochlear Implant Users

Objectives:

Research on cochlear implants (CIs) has focused on speech comprehension, with little research on perception of vocal emotions. We compared emotion perception in CI users and normal-hearing (NH) individuals, using parameter-specific voice morphing.

Design:

Twenty-five CI users and 25 NH individuals (matched for age and gender) performed fearful-angry discriminations on bisyllabic pseudoword stimuli from morph continua across all acoustic parameters (Full), or across selected parameters (F0, Timbre, or Time information), with other parameters set to a noninformative intermediate level.

Results:

Unsurprisingly, CI users as a group showed lower performance in vocal emotion perception overall. Importantly, while NH individuals used timbre and fundamental frequency (F0) information to equivalent degrees, CI users were far more efficient in using timbre (compared to F0) information for this task. Thus, under the conditions of this task, CIs were inefficient in conveying emotion based on F0 alone. There was enormous variability between CI users, with low performers responding close to guessing level. Echoing previous research, we found that better vocal emotion perception was associated with better quality of life ratings.

Conclusions:

Some CI users can utilize timbre cues remarkably well when perceiving vocal emotions.

The effects of lexical content, acoustic and linguistic variability, and vocoding on voice cue perception

Perceptual differences in voice cues, such as fundamental frequency (F0) and vocal tract length (VTL), can facilitate speech understanding in challenging conditions. Yet, we hypothesized that in the presence of spectrotemporal signal degradations, as imposed by cochlear implants (CIs) and vocoders, acoustic cues that overlap for voice perception and phonemic categorization could be mistaken for one another, leading to a strong interaction between linguistic and indexical (talker-specific) content. Fifteen normal-hearing participants performed an odd-one-out adaptive task measuring just-noticeable differences (JNDs) in F0 and VTL. Items used were words (lexical content) or time-reversed words (no lexical content). The use of lexical content was either promoted (by using variable items across comparison intervals) or not (fixed item). Finally, stimuli were presented without or with vocoding. Results showed that JNDs for both F0 and VTL were significantly smaller (better) for non-vocoded compared with vocoded speech and for fixed compared with variable items. Lexical content (forward vs reversed) affected VTL JNDs in the variable item condition, but F0 JNDs only in the non-vocoded, fixed condition. In conclusion, lexical content had a positive top-down effect on VTL perception when acoustic and linguistic variability was present but not on F0 perception. Lexical advantage persisted in the most degraded conditions and vocoding even enhanced the effect of item variability, suggesting that linguistic content could support compensation for poor voice perception in CI users.

Sex-mismatch benefit for speech-in-speech recognition by pediatric and adult cochlear implant users

This project investigated whether pediatric (5-14 years) and adult (30-60 years) cochlear implant (CI) users benefit from a target/masker sex-mismatch for speech-in-speech recognition. Speech recognition thresholds were estimated in a two-male-talker or a two-female-talker masker. Target and masker speech were either sex-matched or sex-mismatched. For both age groups, performance for sex-matched talkers was worse for male than female speech. Sex-mismatch benefit was observed for the two-male-talker masker, indicating CI users can benefit from a target/masker sex mismatch. No benefit was observed for the two-female-talker masker, suggesting this effect may depend on the relative contributions of energetic and informational masking.

Masking Effects in the Perception of Multiple Simultaneous Talkers in Normal-Hearing and Cochlear Implant Listeners

For normal-hearing (NH) listeners, monaural factors, such as voice pitch cues, may play an important role in the segregation of speech signals in multitalker environments. However, cochlear implant (CI) users experience difficulties in segregating speech signals in multitalker environments in part due to the coarse spectral resolution. The present study examined how the vocal characteristics of the target and masking talkers influence listeners’ ability to extract information from a target phrase in a multitalker environment. Speech recognition thresholds (SRTs) were measured with one, two, or four masker talkers for different combinations of target-masker vocal characteristics in 10 adult Mandarin-speaking NH listeners and 12 adult Mandarin-speaking CI users. The results showed that CI users performed significantly poorer than NH listeners in the presence of competing talkers. As the number of masker talkers increased, the mean SRTs significantly worsened from –22.0 dB to –5.2 dB for NH listeners but significantly improved from 5.9 dB to 2.8 dB for CI users. The results suggest that the flattened peaks and valleys with increased numbers of competing talkers may reduce NH listeners’ ability to use dips in the spectral and temporal envelopes that allow for “glimpses” of the target speech. However, the flattened temporal envelope of the resultant masker signals may be less disruptive to the amplitude contour of the target speech, which is important for Mandarin-speaking CI users’ lexical tone recognition. The amount of masking release was further estimated by comparing SRTs between the same-sex maskers and the different-sex maskers. There was a large amount of masking release in NH adults (12 dB) and a small but significant amount of masking release in CI adults (2 dB). These results suggest that adult CI users may significantly benefit from voice pitch differences between target and masker speech.