Speech Intelligibility Benefit Research Articles

Arabic speech intelligibility: Perception of spoken Arabic by native and non-native speakers

Previous studies have shown that native language backgrounds of both talkers and listeners affect speech intelligibility. This study investigated the interlanguage speech intelligibility benefit (ISIB) that is also known as the advantage in understanding second language (L2) speech that non-native listeners have over native listeners when both groups listen to speakers with the same first language (L1). More specifically, it looked into the ISIB in relation to the Arabic language spoken by both native Arabic (NA) and English speakers. To this end, 15 NA and 15 native English (NE) subjects listened to Arabic produced by two groups of talkers (5 NA talkers and 5 NE talkers) and were asked to identify the words they heard. Results showed evidence for the interlanguage speech intelligibility for listeners (i.e. NE listeners were more accurate than NA listeners at identifying English-accented Arabic speech). However, no evidence for the ISIB for talkers was found. That is, NE listeners did not find English-accented speech more intelligible than NA speech. By examining L2 learners’ recognition of L2 consonant contrasts, the study contributes to the body of knowledge on L2 sound acquisition as well as the ISIB literature. It also provides some insight into the problem of adult L2 learners’ ability to learn novel L2 consonants.

Neural envelope tracking predicts speech intelligibility and hearing aid benefit in children with hearing loss

Early assessment of hearing aid benefit is crucial, as the extent to which hearing aids provide audible speech information predicts speech and language outcomes. A growing body of research has proposed neural envelope tracking as an objective measure of speech intelligibility, particularly for individuals unable to provide reliable behavioral feedback. However, its potential for evaluating speech intelligibility and hearing aid benefit in children with hearing loss remains unexplored. In this study, we investigated neural envelope tracking in children with permanent hearing loss through two separate experiments. EEG data were recorded while children listened to age-appropriate stories (Experiment 1) or an animated movie (Experiment 2) under aided and unaided conditions (using personal hearing aids) at multiple stimulus intensities. Neural envelope tracking was evaluated using a linear decoder reconstructing the speech envelope from the EEG in the delta band (0.5-4 Hz). Additionally, we calculated temporal response functions (TRFs) to investigate the spatio-temporal dynamics of the response. In both experiments, neural tracking increased with increasing stimulus intensity, but only in the unaided condition. In the aided condition, neural tracking remained stable across a wide range of intensities, as long as speech intelligibility was maintained. Similarly, TRF amplitudes increased with increasing stimulus intensity in the unaided condition, while in the aided condition significant differences were found in TRF latency rather than TRF amplitude. This suggests that decreasing stimulus intensity does not necessarily impact neural tracking. Furthermore, the use of personal hearing aids significantly enhanced neural envelope tracking, particularly in challenging speech conditions that would be inaudible when unaided. Finally, we found a strong correlation between neural envelope tracking and behaviorally measured speech intelligibility for both narrated stories (Experiment 1) and movie stimuli (Experiment 2). Altogether, these findings indicate that neural envelope tracking could be a valuable tool for predicting speech intelligibility benefits derived from personal hearing aids in hearing-impaired children. Incorporating narrated stories or engaging movies expands the accessibility of these methods even in clinical settings, offering new avenues for using objective speech measures to guide pediatric audiology decision-making.

Perception and production of Mandarin-Accented English: The effect of degree of Accentedness on the Interlanguage Speech Intelligibility Benefit for Listeners (ISIB-L) and Talkers (ISIB-T)

Previous research on the Interlanguage Speech Intelligibility Benefit (ISIB) indicates nonnative listeners may have an advantage at understanding nonnative speech of talkers with the same first language (L1) due to shared interlanguage knowledge. The present study offers a comprehensive analysis of various factors that may modulate this advantage, including the proficiency of both the listeners and the talkers, the mapping of phonemes between the L1 and second language (L2), and the acoustic properties of the phones. Accuracy scores on a lexical decision task were used to investigate both native English listeners’ and native Mandarin learners’ of English perception of native English and Mandarin-accented English speech. Results show clear ISIB-L and ISIB-T effects and demonstrate the dynamic nature of ISIB effects, with both being modulated by speaker and listener proficiency. More striking ISIB effects typically occur at the most extreme ends of accentedness. Additionally, an advantage for common-phoneme over unique-phoneme words in nonnative speech was observed. While nonnative productions of common-phoneme words are more accurate than those of unique-phoneme words, for the most accented productions, nonnative listeners are faster to respond to these unique, often mispronounced, productions.The nonnative listener advantage at perceiving nonnative speech depends on various factors, including listener proficiency, speaker proficiency, phoneme characteristics, and the acoustics of specific speech tokens.

A Visual Speech Intelligibility Benefit Based on Speech Rhythm

This study examined whether visual speech provides speech-rhythm information that perceivers can use in speech perception. This was tested by using speech that naturally varied in the familiarity of its rhythm. Thirty Australian English L1 listeners performed a speech perception in noise task with English sentences produced by three speakers: an English L1 speaker (familiar rhythm); an experienced English L2 speaker who had a weak foreign accent (familiar rhythm), and an inexperienced English L2 speaker who had a strong foreign accent (unfamiliar speech rhythm). The spoken sentences were presented in three conditions: Audio-Only (AO), Audio-Visual with mouth covered (AVm), and Audio-Visual (AV). Speech was best recognized in the AV condition regardless of the degree of foreign accent. However, speech recognition in AVm was better than AO for the speech with no foreign accent and with a weak accent, but not for the speech with a strong accent. A follow-up experiment was conducted that only used the speech with a strong foreign accent, under more audible conditions. The results also showed no difference between the AVm and AO conditions, indicating the null effect was not due to a floor effect. We propose that speech rhythm is conveyed by the motion of the jaw opening and closing, and perceivers use this information to better perceive speech in noise.

An Update on Apraxia of Speech.

Apraxia of speech (AOS) is a motor speech disorder that has long been recognized to occur secondary to acute neurologic insults and, more recently, to neurodegenerative diseases as a harbinger for progressive supranuclear palsy and corticobasal syndrome. This article reviews recent findings regarding the clinic phenotypes of AOS, neuroimaging correlates, and the underlying disease processes. Two clinical subtypes of AOS map onto two underlying 4-repeat tauopathies. New imaging techniques have recently been applied to the study of progressive AOS. There is no data on the impact of behavioral intervention, although studies of nonfluent/agrammatic primary progressive aphasia that include patients with AOS suggest some benefit in speech intelligibility and maintenance. While recent findings suggest subtypes of AOS exist that are linked to molecular pathology and have important implications for disease progression, further research is needed to assess outcome of behavioral and other types of intervention.

Short Implicit Voice Training Affects Listening Effort During a Voice Cue Sensitivity Task With Vocoder-Degraded Speech.

Understanding speech in real life can be challenging and effortful, such as in multiple-talker listening conditions. Fundamental frequency ( fo ) and vocal-tract length ( vtl ) voice cues can help listeners segregate between talkers, enhancing speech perception in adverse listening conditions. Previous research showed lower sensitivity to fo and vtl voice cues when speech signal was degraded, such as in cochlear implant hearing and vocoder-listening compared to normal hearing, likely contributing to difficulties in understanding speech in adverse listening. Nevertheless, when multiple talkers are present, familiarity with a talker's voice, via training or exposure, could provide a speech intelligibility benefit. In this study, the objective was to assess how an implicit short-term voice training could affect perceptual discrimination of voice cues ( fo+vtl ), measured in sensitivity and listening effort, with or without vocoder degradations. Voice training was provided via listening to a recording of a book segment for approximately 30 min, and answering text-related questions, to ensure engagement. Just-noticeable differences (JNDs) for fo+vtl were measured with an odd-one-out task implemented as a 3-alternative forced-choice adaptive paradigm, while simultaneously collecting pupil data. The reference voice either belonged to the trained voice or an untrained voice. Effects of voice training (trained and untrained voice), vocoding (non-vocoded and vocoded), and item variability (fixed or variable consonant-vowel triplets presented across three items) on voice cue sensitivity ( fo+vtl JNDs) and listening effort (pupillometry measurements) were analyzed. Results showed that voice training did not have a significant effect on voice cue discrimination. As expected, fo+vtl JNDs were significantly larger for vocoded conditions than for non-vocoded conditions and with variable item presentations than fixed item presentations. Generalized additive mixed models analysis of pupil dilation over the time course of stimulus presentation showed that pupil dilation was significantly larger during fo+vtl discrimination while listening to untrained voices compared to trained voices, but only for vocoder-degraded speech. Peak pupil dilation was significantly larger for vocoded conditions compared to non-vocoded conditions and variable items increased the pupil baseline relative to fixed items, which could suggest a higher anticipated task difficulty. In this study, even though short voice training did not lead to improved sensitivity to small fo+vtl voice cue differences at the discrimination threshold level, voice training still resulted in reduced listening effort for discrimination among vocoded voice cues.

Improving the Efficiency of Dysarthria Voice Conversion System Based on Data Augmentation.

Dysarthria, a speech disorder often caused by neurological damage, compromises the control of vocal muscles in patients, making their speech unclear and communication troublesome. Recently, voice-driven methods have been proposed to improve the speech intelligibility of patients with dysarthria. However, most methods require a significant representation of both the patient's and target speaker's corpus, which is problematic. This study aims to propose a data augmentation-based voice conversion (VC) system to reduce the recording burden on the speaker. We propose dysarthria voice conversion 3.1 (DVC 3.1) based on a data augmentation approach, including text-to-speech and StarGAN-VC architecture, to synthesize a large target and patient-like corpus to lower the burden of recording. An objective evaluation metric of the Google automatic speech recognition (Google ASR) system and a listening test were used to demonstrate the speech intelligibility benefits of DVC 3.1 under free-talk conditions. The DVC system without data augmentation (DVC 3.0) was used for comparison. Subjective and objective evaluation based on the experimental results indicated that the proposed DVC 3.1 system enhanced the Google ASR of two dysarthria patients by approximately [62.4%, 43.3%] and [55.9%, 57.3%] compared to unprocessed dysarthria speech and the DVC 3.0 system, respectively. Further, the proposed DVC 3.1 increased the speech intelligibility of two dysarthria patients by approximately [54.2%, 22.3%] and [63.4%, 70.1%] compared to unprocessed dysarthria speech and the DVC 3.0 system, respectively. The proposed DVC 3.1 system offers significant potential to improve the speech intelligibility performance of patients with dysarthria and enhance verbal communication quality.

Non-native talkers and listeners and the perceptual benefits of clear speech.

This study examined the intelligibility benefit of native and non-native clear speech for native and non-native listeners when the first language background of non-native talkers and listeners is matched. All four combinations of talkers and listeners were tested: native talker-native listener, non-native talker-native listener, native talker-non-native listener, and non-native talker-non-native listener. Listeners were presented with structurally simple but semantically anomalous English sentences produced clearly or casually and mixed with speech-shaped noise at 0 dB signal-to-noise ratio and asked to write down what they heard. Results showed that native English speech was more intelligible than non-native speech and that native English listeners recovered speech better than non-native listeners did. Clear speech was significantly more intelligible than casual speech. There were no interactions between speaking style and native language background indicating that clear speech intelligibility benefit was not significantly different across distinct combinations of talkers and listeners. In particular, shared first language background among non-native speakers and listeners did not provide an extra benefit in either the overall speech intelligibility or the intelligibility gains of clear speech.

Interaural speech asymmetry predicts bilateral speech intelligibility but not listening effort in adults with bilateral cochlear implants.

Bilateral cochlear implants (BiCIs) can facilitate improved speech intelligibility in noise and sound localization abilities compared to a unilateral implant in individuals with bilateral severe to profound hearing loss. Still, many individuals with BiCIs do not benefit from binaural hearing to the same extent that normal hearing (NH) listeners do. For example, binaural redundancy, a speech intelligibility benefit derived from having access to duplicate copies of a signal, is highly variable among BiCI users. Additionally, patients with hearing loss commonly report elevated listening effort compared to NH listeners. There is some evidence to suggest that BiCIs may reduce listening effort compared to a unilateral CI, but the limited existing literature has not shown this consistently. Critically, no studies to date have investigated this question using pupillometry to quantify listening effort, where large pupil sizes indicate high effort and small pupil sizes indicate low effort. Thus, the present study aimed to build on existing literature by investigating the potential benefits of BiCIs for both speech intelligibility and listening effort. Twelve BiCI adults were tested in three listening conditions: Better Ear, Poorer Ear, and Bilateral. Stimuli were IEEE sentences presented from a loudspeaker at 0° azimuth in quiet. Participants were asked to repeat back the sentences, and responses were scored by an experimenter while changes in pupil dilation were measured. On average, participants demonstrated similar speech intelligibility in the Better Ear and Bilateral conditions, and significantly worse speech intelligibility in the Poorer Ear condition. Despite similar speech intelligibility in the Better Ear and Bilateral conditions, pupil dilation was significantly larger in the Bilateral condition. These results suggest that the BiCI users tested in this study did not demonstrate binaural redundancy in quiet. The large interaural speech asymmetries demonstrated by participants may have precluded them from obtaining binaural redundancy, as shown by the inverse relationship between the two variables. Further, participants did not obtain a release from effort when listening with two ears versus their better ear only. Instead, results indicate that bilateral listening elicited increased effort compared to better ear listening, which may be due to poor integration of asymmetric inputs.

When A Nonnative Accent Lets You Spot All the Errors: Examining the Syntactic Interlanguage Benefit.

In our continuously globalizing world, cross-cultural and cross-linguistic communications are far from exceptional. A wealth of research has indicated that the processing of nonnative-accented speech can be challenging for native listeners, both at the level of phonology. However, few online studies have examined the underpinnings of accented speech recognition from the perspective of the nonnative listener, even though behavioral studies indicate that accented input may be easier to process for such individuals (i.e., the interlanguage speech intelligibility benefit. The current EEG study first examined the phonological and syntactic analysis of nonnative-accented speech among nonnative listeners. As such, 30 English learners of Spanish listened to syntactically correct and incorrect Spanish sentences produced in native and nonnative-accented Spanish. The violation in the incorrect sentences was caused by errors that are typical (i.e., gender errors; *la color) or atypical (i.e., number errors; *los color) for English learners of Spanish. Results indicated that nonnative listeners elicit a phonological mismatch negativity (PMN) when attending to speech produced by a native Spanish speaker. Furthermore, the nonnative listeners showed a P600 for all grammatical violations, indicating that they repair all errors regardless of their typicality or the accent in which they are produced. Follow-up analyses compared our novel data to the data of native listeners from the methodologically identical precursor study. These analyses showed that native and nonnative listeners exhibit directionally opposite PMN effects; whereas natives exhibited a larger PMN for English-accented Spanish, nonnatives displayed a larger PMN in response to native Spanish utterances (a classic interlanguage speech intelligibility benefit). An additional difference was observed at the syntactic level: Whereas natives repaired only atypical number errors when they were English-accented, nonnative participants exhibited a P600 in response to all English-accented syntactic errors, regardless of their typicality (a syntactic interlanguage speech intelligibility benefit). Altogether, these results suggest that accented speech is not inherently difficult to process; in fact, nonnatives may benefit from the presence of a nonnative accent. Thus, our data provide some of the first electrophysiological evidence supporting the existence of the classic interlanguage speech intelligibility benefit and its novel syntactic counterpart.

Matched-accent processing: Bulgarian-English bilinguals do not have a processing advantage with Bulgarian-accented English over native English speech

The Interlanguage Speech Intelligibility Benefit (ISIB) hypothesis for Talkers suggests that there is a potential benefit when listening to one’s second language when it is produced in the accent of one’s first language (matched-accent processing). This study explores ISIB, considering listener proficiency. According to second language learning theories, the listener’s second language proficiency determines the extent to which they rely on their first language phonetics, hence the magnitude of ISIB may be affected by listener proficiency. The accuracy and reaction times of Bulgarian-English bilinguals living in the UK were recorded in a lexical decision task. The English stimuli were produced by native English speakers and Bulgarian-English bilinguals. Listeners responded more slowly and less accurately to the matched-accent stimuli than the native English stimuli. In addition, they adapted their reaction times faster to new speakers with a native English accent compared to a Bulgarian accent. However, the listeners with the lowest English proficiency had no advantage in reaction times and accuracy for either accent. The results offer mixed support for ISIB for Talkers, and are consistent with second language learning theories according to which listeners rely less on their native language phonology when their proficiency in the second language has increased.

The Interlanguage Speech Intelligibility Benefit for Turkish Speakers of English

This study is aimed at investigating the Interlanguage Speech Intelligibility Benefit (ISIB) via native English and Turkish listeners’ transcriptions of Turkish talkers’ words with pronunciation errors in English. Speech samples collected from talkers with a Turkish L1 background (N=16) were presented to 33 L1 English and 33 L1 Turkish listeners via an instrument to be filled with the transcriptions of erroneous target words. Results supported matched ISIB for listeners as Turkish talkers were more intelligible to Turkish listeners in a considerably higher number of target words. Similarly, a higher number of target words were more intelligible to Turkish listeners with statistically significant differences. Most of these words had been labelled erroneous due to L1 transfer caused by orthographic interference, mispronunciations of English sounds that do not exist in Turkish, and loanwords found in similar forms in Turkish. Turkish listeners appeared to rely on such cues in Turkish talkers’ speech.

The clear speech intelligibility benefit for text-to-speech voices: Effects of speaking style and visual guise

This study examined how speaking style and guise influence the intelligibility of text-to-speech (TTS) and naturally produced human voices. Results showed that TTS voices were less intelligible overall. Although using a clear speech style improved intelligibility for both human and TTS voices (using "newscaster" neural TTS), the clear speech effect was stronger for TTS voices. Finally, a visual device guise decreased intelligibility, regardless of voice type. The results suggest that both speaking style and visual guise affect intelligibility of human and TTS voices. Findings are discussed in terms of theories about the role of social information in speech perception.

The role of proficiency in the interlanguage speech intelligibility benefit

Previous research indicates nonnative listeners may have an advantage at understanding nonnative speech of talkers with the same L1 due to shared interlanguage knowledge. The present study offers a comprehensive analysis of various factors that may modulate this advantage, including the proficiency of interlocutors, the mapping of phonemes between the L1 and L2, and the acoustic properties of the phonemes. Accuracy scores on a lexical decision task were used to identify whether native Mandarin learners of English are better than native English listeners at perceiving Mandarin-accented English speech, as well as whether they are better at perceiving Mandarin-accented English compared to native English speech. Results indicated an overall native English interlocutor advantage, an advantage for common-phoneme over unique-phoneme words in nonnative speech, and some evidence of gradience in ISIB effects based on the proficiency of talkers and listeners. No strong relationship between type of English input (native or accented) and the ability to understand Mandarin-accented English speech was found. The nonnative listener advantage at perceiving nonnative speech is relatively small and depends on various factors, including listener proficiency, speaker proficiency, phoneme characteristics, and the acoustics of specific speech tokens.

Intelligibility of Noise-Adapted and Clear Speech in Energetic and Informational Maskers for Native and Nonnative Listeners.

This study explored clear speech (CS) and noise-adapted speech (NAS) intelligibility benefits for native and nonnative English listeners. It also examined how the two speaking style adaptations interact with maskers that vary from purely energetic to largely informational at different signal-to-noise ratios (SNRs). Materials consisted of 40 sentences produced by 10 young adult talkers in a conversational and a clear speaking style under two conditions: (a) in quiet and (b) in response to speech-shaped noise (SSN) played over headphones (NAS). Young adult native (Experiment 1) and nonnative (Experiment 2) English listeners heard target sentences presented in two-talker (2T) babble, six-talker (6T) babble, or SSN and at an "easier" and a "harder" SNR. When talkers produced CS and NAS, word recognition accuracy was significantly improved for both listener groups. The largest intelligibility benefit was obtained for the CS produced in response to noise (CS+NAS). Overall accuracy was highest in 2T babble. Accuracy was higher in SSN than in 6T babble for nonnative listeners at both levels of listening difficulty but only at a more difficult SNR for native listeners. Listeners benefited from CS and NAS most in the presence of SSN and least in 2T babble. When SNRs were the same for the two listener groups, native listeners outperformed nonnative listeners in almost all listening conditions, but nonnative listeners benefited more from CS and NAS in 6T babble than native listeners did. Combined speaking style enhancements, CS+NAS, provided the largest intelligibility increases for native and nonnative listeners in all listening conditions. The results add to the body of evidence supporting speech-oriented, behavioral therapy techniques for maximizing speech intelligibility in everyday listening situations.

OPRA-RS: A Hearing-Aid Fitting Method Based on Automatic Speech Recognition and Random Search.

Hearing-aid (HA) prescription rules (such as NAL-NL2, DSL-v5, and CAM2) are used by HA audiologists to define initial HA settings (e.g., insertion gains, IGs) for patients. This initial fitting is later individually adjusted for each patient to improve clinical outcomes in terms of speech intelligibility and listening comfort. During this fine-tuning stage, speech-intelligibility tests are often carried out with the patient to assess the benefits associated with different HA settings. As these tests tend to be time-consuming and performance on them depends on the patient's level of fatigue and familiarity with the test material, only a limited number of HA settings can be explored. Consequently, it is likely that a suboptimal fitting is used for the patient. Recent studies have shown that automatic speech recognition (ASR) can be used to predict the effects of IGs on speech intelligibility for patients with age-related hearing loss (ARHL). The aim of the present study was to extend this approach by optimizing, in addition to IGs, compression thresholds (CTs). However, increasing the number of parameters to be fitted increases exponentially the number of configurations to be assessed. To limit the number of HA settings to be tested, three random-search (RS) genetic algorithms were used. The resulting new HA fitting method, combining ASR and RS, is referred to as “objective prescription rule based on ASR and random search" (OPRA-RS). Optimal HA settings were computed for 12 audiograms, representing average and individual audiometric profiles typical for various levels of ARHL severity, and associated ASR performances were compared to those obtained with the settings recommended by CAM2. Each RS algorithm was run twice to assess its reliability. For all RS algorithms, ASR scores obtained with OPRA-RS were significantly higher than those associated with CAM2. Each RS algorithm converged on similar optimal HA settings across repetitions. However, significant differences were observed between RS algorithms in terms of maximum ASR performance and processing costs. These promising results open the way to the use of ASR and RS algorithms for the fine-tuning of HAs with potential speech-intelligibility benefits for the patient.

Predictive Sentence Context Reduces Listening Effort in Older Adults With and Without Hearing Loss and With High and Low Working Memory Capacity.

Listening effort is needed to understand speech that is degraded by hearing loss, a noisy environment, or both. This in turn reduces cognitive spare capacity, the amount of cognitive resources available for allocation to concurrent tasks. Predictive sentence context enables older listeners to perceive speech more accurately, but how does contextual information affect older adults' listening effort? The current study examines the impacts of sentence context and cognitive (memory) load on sequential dual-task behavioral performance in older adults. To assess whether effects of context and memory load differ as a function of older listeners' hearing status, baseline working memory capacity, or both, effects were compared across separate groups of participants with and without hearing loss and with high and low working memory capacity. Participants were older adults (age 60-84 years; n = 63) who passed a screen for cognitive impairment. A median split classified participants into groups with high and low working memory capacity. On each trial, participants listened to spoken sentences in noise and reported sentence-final words that were either predictable or unpredictable based on sentence context, and also recalled short (low-load) or long (high-load) sequences of digits that were presented visually before each spoken sentence. Speech intelligibility was quantified as word identification accuracy, and measures of listening effort included digit recall accuracy, and response time to words and digits. Correlations of context benefit in each dependent measure with working memory and vocabulary were also examined. Across all participant groups, accuracy and response time for both word identification and digit recall were facilitated by predictive context, indicating that in addition to an improvement in intelligibility, listening effort was also reduced when sentence-final words were predictable. Effects of predictability on all listening effort measures were observed whether or not trials with an incorrect word identification response were excluded, indicating that the effects of predictability on listening effort did not depend on speech intelligibility. In addition, although cognitive load did not affect word identification accuracy, response time for word identification and digit recall, as well as accuracy for digit recall, were impaired under the high-load condition, indicating that cognitive load reduced the amount of cognitive resources available for speech processing. Context benefit in speech intelligibility was positively correlated with vocabulary. However, context benefit was not related to working memory capacity. Predictive sentence context reduces listening effort in cognitively healthy older adults resulting in greater cognitive spare capacity available for other mental tasks, irrespective of the presence or absence of hearing loss and baseline working memory capacity.

Phonetic posteriorgram-based voice conversion system to improve speech intelligibility of dysarthric patients

Background and ObjectiveMost dysarthric patients encounter communication problems due to unintelligible speech. Currently, there are many voice-driven systems aimed at improving their speech intelligibility; however, the intelligibility performance of these systems are affected by challenging application conditions (e.g., time variance of patient's speech and background noise). To alleviate these problems, we proposed a dysarthria voice conversion (DVC) system for dysarthric patients and investigated the benefits under challenging application conditions. MethodA deep learning-based voice conversion system with phonetic posteriorgram (PPG) features, called the DVC-PPG system, was proposed in this study. An objective-evaluation metric of Google automatic speech recognition (Google ASR) system and a listening test were used to demonstrate the speech intelligibility benefits of DVC-PPG under quiet and noisy test conditions; besides, the well-known voice conversion system using mel-spectrogram, DVC-Mels, was used for comparison to verify the benefits of the proposed DVC-PPG system. ResultsThe objective-evaluation metric of Google ASR showed the average accuracy of two subjects in the duplicate and outside test conditions while the DVC-PPG system provided higher speech recognitions rate (83.2% and 67.5%) than dysarthric speech (36.5% and 26.9%) and DVC-Mels (52.9% and 33.8%) under quiet conditions. However, the DVC-PPG system provided more stable performance than the DVC-Mels under noisy test conditions. In addition, the results of the listening test showed that the speech-intelligibility performance of DVC-PPG was better than those obtained via the dysarthria speech and DVC-Mels under the duplicate and outside conditions, respectively. ConclusionsThe objective-evaluation metric and listening test results showed that the recognition rate of the proposed DVC-PPG system was significantly higher than those obtained via the original dysarthric speech and DVC-Mels system. Therefore, it can be inferred from our study that the DVC-PPG system can improve the ability of dysarthric patients to communicate with people under challenging application conditions.

Novel Approaches to Measure Spatial Release From Masking in Children With Bilateral Cochlear Implants.

To investigate the role of auditory cues for spatial release from masking (SRM) in children with bilateral cochlear implants (BiCIs) and compare their performance with children with normal hearing (NH). To quantify the contribution to speech intelligibility benefits from individual auditory cues: head shadow, binaural redundancy, and interaural differences; as well as from multiple cues: SRM and binaural squelch. To assess SRM using a novel approach of adaptive target-masker angular separation, which provides a more functionally relevant assessment in realistic complex auditory environments. Children fitted with BiCIs (N = 11) and with NH (N = 18) were tested in virtual acoustic space that was simulated using head-related transfer functions measured from individual children with BiCIs behind the ear and from a standard head and torso simulator for all NH children. In experiment I, by comparing speech reception thresholds across 4 test conditions that varied in target-masker spatial separation (colocated versus separated at 180°) and listening conditions (monaural versus binaural/bilateral listening), intelligibility benefits were derived for individual auditory cues for SRM. In experiment II, SRM was quantified using a novel measure to find the minimum angular separation (MAS) between the target and masker to achieve a fixed 20% intelligibility improvement. Target speech was fixed at either +90 or -90° azimuth on the side closer to the better ear (+90° for all NH children) and masker locations were adaptively varied. In experiment I, children with BiCIs as a group had smaller intelligibility benefits from head shadow than NH children. No group difference was observed in benefits from binaural redundancy or interaural difference cues. In both groups of children, individuals who gained a larger benefit from interaural differences relied less on monaural head shadow, and vice versa. In experiment II, all children with BiCIs demonstrated measurable MAS thresholds <180° and on average larger than that from NH children. Eight of 11 children with BiCIs and all NH children had a MAS threshold <90°, requiring interaural differences only to gain the target intelligibility benefit; whereas the other 3 children with BiCIs had a MAS between 120° and 137°, requiring monaural head shadow for SRM. When target and maskers were separated at 180° on opposing hemifields, children with BiCIs demonstrated greater intelligibility benefits from head shadow and interaural differences than previous literature showed with a smaller separation. Children with BiCIs demonstrated individual differences in using auditory cues for SRM. From the MAS thresholds, more than half of the children with BiCIs demonstrated robust access to interaural differences without needing additional monaural head shadow for SRM. Both experiments led to the conclusion that individualized fitting strategies in the bilateral devices may be warranted to maximize spatial hearing for children with BiCIs in complex auditory environments.

How Long Does It Take for a Voice to Become Familiar? Speech Intelligibility and Voice Recognition Are Differentially Sensitive to Voice Training

When people listen to speech in noisy places, they can understand more words spoken by someone familiar, such as a friend or partner, than someone unfamiliar. Yet we know little about how voice familiarity develops over time. We exposed participants (N = 50) to three voices for different lengths of time (speaking 88, 166, or 478 sentences during familiarization and training). These previously heard voices were recognizable and more intelligible when presented with a competing talker than novel voices—even the voice previously heard for the shortest duration. However, recognition and intelligibility improved at different rates with longer exposures. Whereas recognition was similar for all previously heard voices, intelligibility was best for the voice that had been heard most extensively. The speech-intelligibility benefit for the most extensively heard voice (10%–15%) is as large as that reported for voices that are naturally very familiar (friends and spouses)—demonstrating that the intelligibility of a voice can be improved substantially after only an hour of training.