On the Feasibility of Using Behavioral Listening Effort Test Methods to Evaluate Auditory Performance in Cochlear Implant Users.

Realistic outcome measures that reflect everyday hearing challenges are needed to assess hearing aid and cochlear implant (CI) fitting. Literature suggests that listening effort measures may be more sensitive to differences between hearing-device settings than established speech intelligibility measures when speech intelligibility is near maximum. Which method provides the most effective measurement of listening effort for this purpose is currently unclear. This study aimed to investigate the feasibility of two tests for measuring changes in listening effort in CI users due to signal-to-noise ratio (SNR) differences, as would arise from different hearing-device settings. By comparing the effect size of SNR differences on listening effort measures with test-retest differences, the study evaluated the suitability of these tests for clinical use. Nineteen CI users underwent two listening effort tests at two SNRs (+4 and +8 dB relative to individuals' 50% speech perception threshold). We employed dual-task paradigms-a sentence-final word identification and recall test (SWIRT) and a sentence verification test (SVT)-to assess listening effort at these two SNRs. Our results show a significant difference in listening effort between the SNRs for both test methods, although the effect size was comparable to the test-retest difference, and the sensitivity was not superior to speech intelligibility measures. Thus, the implementations of SVT and SWIRT used in this study are not suitable for clinical use to measure listening effort differences of this magnitude in individual CI users. However, they can be used in research involving CI users to analyze group data.

Loudness Balancing Optimization for Better Speech Intelligibility, Music Perception, and Spectral Temporal Resolution in Cochlear Implant Users.

HYPOTHESIS: The behaviorally based programming with loudness balancing (LB) would result in better speech understanding, spectral-temporal resolution, and music perception scores, and there would be a relationship between these scores. BACKGROUND: Loudness imbalances at upper stimulation levels may cause sounds to be perceived as irregular, gravelly, or overly echoed and may negatively affect the listening performance of the cochlear implant (CI) user. LB should be performed after fitting to overcome these problems. METHODS: The study included 26 unilateral Med-EL CI users. Two different CI programs based on the objective electrically evoked stapedial reflex threshold (P1) and the behaviorally program with LB (P2) were recorded for each participant. The Turkish Matrix Sentence Test (TMS) was applied to evaluate speech perception; the Random Gap Detection Test (RGDT) and Spectral-Temporally Modulated Ripple Test (SMRT) were applied to evaluate spectral temporal resolution skills; the Mini Profile of Music Perception Skills (mini-PROMS) and Melodic Contour Identification (MCI) tests were applied to evaluate music perception, and the results were compared. RESULTS: Significantly better scores were obtained with P2 in TMS tests performed in noise and quiet. SMRT scores were significantly correlated with TMS in quiet and noise, and mini-PROMS sound perception results. Although better scores were obtained with P2 in the mini-PROMS total score and MCI, a significant difference was found only for MCI. CONCLUSION: The data from the current study showed that equalization of loudness across CI electrodes leads to better perceptual acuity. It also revealed the relationship between speech perception, spectral-temporal resolution, and music perception.

Effects of Deep-Brain Stimulation on Speech: Perceptual and Acoustic Data.

PURPOSE: This study examined speech changes induced by deep-brain stimulation (DBS) in speakers with Parkinson's disease (PD) using a set of auditory-perceptual and acoustic measures. METHOD: Speech recordings from nine speakers with PD and DBS were compared between DBS-On and DBS-Off conditions using auditory-perceptual and acoustic analyses. Auditory-perceptual ratings included voice quality, articulation precision, prosody, speech intelligibility, and listening effort obtained from 44 listeners. Acoustic measures were made for voicing proportion, second formant frequency slope, vowel dispersion, articulation rate, and range of fundamental frequency and intensity. RESULTS: No significant changes were found between DBS-On and DBS-Off for the five perceptual ratings. Four of six acoustic measures revealed significant differences between the two conditions. While articulation rate and acoustic vowel dispersion increased, voicing proportion and intensity range decreased from the DBS-Off to DBS-On condition. However, a visual examination of the data indicated that the statistical significance was mostly driven by a small number of participants, while the majority did not show a consistent pattern of such changes. CONCLUSIONS: Our data, in general, indicate no-to-minimal changes in speech production ensued from DBS stimulation. The findings are discussed with a focus on large interspeaker variability in PD in terms of their speech characteristics and the potential effects of DBS on speech.

Combining Cardiovascular and Pupil Features Using k-Nearest Neighbor Classifiers to Assess Task Demand, Social Context, and Sentence Accuracy During Listening.

In daily life, both acoustic factors and social context can affect listening effort investment. In laboratory settings, information about listening effort has been deduced from pupil and cardiovascular responses independently. The extent to which these measures can jointly predict listening-related factors is unknown. Here we combined pupil and cardiovascular features to predict acoustic and contextual aspects of speech perception. Data were collected from 29 adults (mean  =  64.6 years, SD  =  9.2) with hearing loss. Participants performed a speech perception task at two individualized signal-to-noise ratios (corresponding to 50% and 80% of sentences correct) and in two social contexts (the presence and absence of two observers). Seven features were extracted per trial: baseline pupil size, peak pupil dilation, mean pupil dilation, interbeat interval, blood volume pulse amplitude, pre-ejection period and pulse arrival time. These features were used to train k-nearest neighbor classifiers to predict task demand, social context and sentence accuracy. The k-fold cross validation on the group-level data revealed above-chance classification accuracies: task demand, 64.4%; social context, 78.3%; and sentence accuracy, 55.1%. However, classification accuracies diminished when the classifiers were trained and tested on data from different participants. Individually trained classifiers (one per participant) performed better than group-level classifiers: 71.7% (SD  =  10.2) for task demand, 88.0% (SD  =  7.5) for social context, and 60.0% (SD  =  13.1) for sentence accuracy. We demonstrated that classifiers trained on group-level physiological data to predict aspects of speech perception generalized poorly to novel participants. Individually calibrated classifiers hold more promise for future applications.

Automatic recognition of second language speech-in-noise.

Measuring how well human listeners recognize speech under varying environmental conditions (speech intelligibility) is a challenge for theoretical, technological, and clinical approaches to speech communication. The current gold standard-human transcription-is time- and resource-intensive. Recent advances in automatic speech recognition (ASR) systems raise the possibility of automating intelligibility measurement. This study tested 4 state-of-the-art ASR systems with second language speech-in-noise and found that one, whisper, performed at or above human listener accuracy. However, the content of whisper's responses diverged substantially from human responses, especially at lower signal-to-noise ratios, suggesting both opportunities and limitations for ASR--based speech intelligibility modeling.

Original speech and its echo are segregated and separately processed in the human brain.

Speech recognition crucially relies on slow temporal modulations (<16 Hz) in speech. Recent studies, however, have demonstrated that the long-delay echoes, which are common during online conferencing, can eliminate crucial temporal modulations in speech but do not affect speech intelligibility. Here, we investigated the underlying neural mechanisms. MEG experiments demonstrated that cortical activity can effectively track the temporal modulations eliminated by an echo, which cannot be fully explained by basic neural adaptation mechanisms. Furthermore, cortical responses to echoic speech can be better explained by a model that segregates speech from its echo than by a model that encodes echoic speech as a whole. The speech segregation effect was observed even when attention was diverted but would disappear when segregation cues, i.e., speech fine structure, were removed. These results strongly suggested that, through mechanisms such as stream segregation, the auditory system can build an echo-insensitive representation of speech envelope, which can support reliable speech recognition.

ART and AutoART ECAP measurements and cochlear nerve anatomy as predictors in adult cochlear implant recipients.

PURPOSE: The purpose of this retrospective study is to compare the results of electrically evoked compound action potential (ECAP) measurements using automatic auditory response telemetry (AutoART) with those obtained by ART in adults. The study also aimed to evaluate the predictive value of intraoperative ART and AutoART ECAPs for speech intelligibility (SI) and hearing success (HS), and to determine if cochlear nerve (CN) cross-sectional area (CSA) obtained preoperatively by magnetic resonance imaging (MRI) scans could predict ART and AutoART ECAPs and SI and HS outcome. METHODS: The study analyzed and correlated ART and AutoART ECAP thresholds at electrodes E2, E6, and E10, as well as averaged ECAP thresholds over electrodes E1-E12, using data from 32 implants. Correlations were also examined for ART and AutoART ECAP slopes. In addition, averaged ART and AutoART ECAP thresholds and slopes over all 12 electrodes for each participant were correlated with CN CSA measured from MRI sequences. SI of the monosyllabic Freiburg Speech Test at 65 dB sound pressure level was examined along with averaged ART and AutoART thresholds and slopes over all 12 electrodes. A parallel analysis was performed for HS, derived from the difference between baseline and 6-month SI. Finally, correlations between CN CSA and SI, as well as CN CSA and HS were examined. RESULTS: The results of the study showed a significant positive correlation between ART and AutoART ECAP thresholds and as well as slopes for E2, E6, E10 and averaged thresholds and slopes of E1-E12. However, no significant correlation was observed between ART and AutoART averaged ECAP thresholds and slopes and either SI and HS or CN CSA. Furthermore, no significant correlation was found between CN CSA and SI and HS. CONCLUSION: While AutoART is a reliable and safe program for measuring ECAPs in adults, the study found no preoperative prognostic information on intraoperative ECAP results using parameters extracted from current MRI sequences or pre-/intraoperative information on subsequent hearing outcome using ECAP and CN CSA.

The Use of the Voice Trainer App for Vocal Control in People with a Degenerative Ataxia: A Pilot Intervention Study.

Dysarthria is disabling in persons with degenerative ataxia. There is limited evidence for speech therapy interventions. In this pilot study, we used the Voice trainer app, which was originally developed for patients with Parkinson's disease, as a feedback tool for vocal control. We hypothesized that patients with ataxic dysarthria would benefit from the Voice trainer app to better control their loudness and pitch, resulting in a lower speaking rate and better intelligibility. This intervention study consisted of five therapy sessions of 30 min within 3 weeks using the principles of the Pitch Limiting Voice Treatment. Patients received real-time visual feedback on loudness and pitch during the exercises. Besides, they were encouraged to practice at home or to use the Voice trainer in daily life. We used observer-rated and patient-rated outcome measures. The primary outcome measure was intelligibility, as measured by the Dutch sentence intelligibility test. Twenty-one out of 25 included patients with degenerative ataxia completed the therapy. We found no statistically significant improvements in intelligibility (p = .56). However, after the intervention, patients were speaking slower (p = .03) and the pause durations were longer (p < .001). The patients were satisfied about using the app. At the group level, we found no evidence for an effect of the Voice trainer app on intelligibility in degenerative ataxia. Because of the heterogeneity of ataxic dysarthria, a more tailor-made rather than generic intervention seems warranted.

Contributions of listening effort and intelligibility to cortical tracking of speech in adverse listening conditions.

Cortical tracking of speech is vital for speech segmentation and is linked to speech intelligibility. However, there is no clear consensus as to whether reduced intelligibility leads to a decrease or an increase in cortical speech tracking, warranting further investigation of the factors influencing this relationship. One such factor is listening effort, defined as the cognitive resources necessary for speech comprehension, and reported to have a strong negative correlation with speech intelligibility. Yet, no studies have examined the relationship between speech intelligibility, listening effort, and cortical tracking of speech. The aim of the present study was thus to examine these factors in quiet and distinct adverse listening conditions. Forty-nine normal hearing adults listened to sentences produced casually, presented in quiet and two adverse listening conditions: cafeteria noise and reverberant speech. Electrophysiological responses were registered with electroencephalogram, and listening effort was estimated subjectively using self-reported scores and objectively using pupillometry. Results indicated varying impacts of adverse conditions on intelligibility, listening effort, and cortical tracking of speech, depending on the preservation of the speech temporal envelope. The more distorted envelope in the reverberant condition led to higher listening effort, as reflected in higher subjective scores, increased pupil diameter, and stronger cortical tracking of speech in the delta band. These findings suggest that using measures of listening effort in addition to those of intelligibility is useful for interpreting cortical tracking of speech results. Moreover, reading and phonological skills of participants were positively correlated with listening effort in the cafeteria condition, suggesting a special role of expert language skills in processing speech in this noisy condition. Implications for future research and theories linking atypical cortical tracking of speech and reading disorders are further discussed.

Pupil Dilation Reflects Perceptual Priorities During a Receptive Speech Task.

OBJECTIVES: The listening demand incurred by speech perception fluctuates in normal conversation. At the acoustic-phonetic level, natural variation in pronunciation acts as speedbumps to accurate lexical selection. Any given utterance may be more or less phonetically ambiguous-a problem that must be resolved by the listener to choose the correct word. This becomes especially apparent when considering two common speech registers-clear and casual-that have characteristically different levels of phonetic ambiguity. Clear speech prioritizes intelligibility through hyperarticulation which results in less ambiguity at the phonetic level, while casual speech tends to have a more collapsed acoustic space. We hypothesized that listeners would invest greater cognitive resources while listening to casual speech to resolve the increased amount of phonetic ambiguity, as compared with clear speech. To this end, we used pupillometry as an online measure of listening effort during perception of clear and casual continuous speech in two background conditions: quiet and noise. DESIGN: Forty-eight participants performed a probe detection task while listening to spoken, nonsensical sentences (masked and unmasked) while recording pupil size. Pupil size was modeled using growth curve analysis to capture the dynamics of the pupil response as the sentence unfolded. RESULTS: Pupil size during listening was sensitive to the presence of noise and speech register (clear/casual). Unsurprisingly, listeners had overall larger pupil dilations during speech perception in noise, replicating earlier work. The pupil dilation pattern for clear and casual sentences was considerably more complex. Pupil dilation during clear speech trials was slightly larger than for casual speech, across quiet and noisy backgrounds. CONCLUSIONS: We suggest that listener motivation could explain the larger pupil dilations to clearly spoken speech. We propose that, bounded by the context of this task, listeners devoted more resources to perceiving the speech signal with the greatest acoustic/phonetic fidelity. Further, we unexpectedly found systematic differences in pupil dilation preceding the onset of the spoken sentences. Together, these data demonstrate that the pupillary system is not merely reactive but also adaptive-sensitive to both task structure and listener motivation to maximize accurate perception in a limited resource system.

The association between longitudinal declines in speech sound accuracy and speech intelligibility in speakers with amyotrophic lateral sclerosis.

The purpose of this study was to examine how neurodegeneration secondary to amyotrophic lateral sclerosis (ALS) impacts speech sound accuracy over time and how speech sound accuracy, in turn, is related to speech intelligibility. Twenty-one participants with ALS read the Bamboo Passage over multiple data collection sessions across several months. Phonemic and orthographic transcriptions were completed for all speech samples. The percentage of phonemes accurately produced was calculated across each phoneme, sound class (i.e. consonants versus vowels), and distinctive feature (i.e. features involved in Manner of Articulation, Place of Articulation, Laryngeal Voicing, Tongue Height, and Tongue Advancement). Intelligibility was determined by calculating the percentage of words correctly transcribed orthographically by naive listeners. Linear mixed effects models were conducted to assess the decline of each distinctive feature over time and its impact on intelligibility. The results demonstrated that overall phonemic production accuracy had a nonlinear relationship with speech intelligibility and that a subset of features (i.e. those dependent on precise lingual and labial constriction and/or extensive lingual and labial movement) were more important for intelligibility and were more impacted over time than other features. Furthermore, findings revealed that consonants were more strongly associated with intelligibility than vowels, but consonants did not significantly differ from vowels in their decline over time. These findings have the potential to (1) strengthen mechanistic understanding of the physiological constraints imposed by neuronal degeneration on speech production and (2) inform the timing and selection of treatment and assessment targets for individuals with ALS.

Pupillometry reveals differences in cognitive demands of listening to face mask-attenuated speech.

Face masks offer essential protection but also interfere with speech communication. Here, audio-only sentences spoken through four types of masks were presented in noise to young adult listeners. Pupil dilation (an index of cognitive demand), intelligibility, and subjective effort and performance ratings were collected. Dilation increased in response to each mask relative to the no-mask condition and differed significantly where acoustic attenuation was most prominent. These results suggest that the acoustic impact of the mask drives not only the intelligibility of speech, but also the cognitive demands of listening. Subjective effort ratings reflected the same trends as the pupil data.

The Involvement of Listening Effort in Explaining Bilingual Listening Under Adverse Listening Conditions.

The current review examines listening effort to uncover how it is implicated in bilingual performance under adverse listening conditions. Various measures of listening effort, including physiological, behavioral, and subjective measures, have been employed to examine listening effort in bilingual children and adults. Adverse listening conditions, stemming from environmental factors, as well as factors related to the speaker or listener, have been examined. The existing literature, although relatively limited to date, points to increased listening effort among bilinguals in their nondominant second language (L2) compared to their dominant first language (L1) and relative to monolinguals. Interestingly, increased effort is often observed even when speech intelligibility remains unaffected. These findings emphasize the importance of considering listening effort alongside speech intelligibility. Building upon the insights gained from the current review, we propose that various factors may modulate the observed effects. These include the particular measure selected to examine listening effort, the characteristics of the adverse condition, as well as factors related to the particular linguistic background of the bilingual speaker. Critically, further research is needed to better understand the impact of these factors on listening effort. The review outlines avenues for future research that would promote a comprehensive understanding of listening effort in bilingual individuals.

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.

Neural tracking measures of speech intelligibility: Manipulating intelligibility while keeping acoustics unchanged.

Neural speech tracking has advanced our understanding of how our brains rapidly map an acoustic speech signal onto linguistic representations and ultimately meaning. It remains unclear, however, how speech intelligibility is related to the corresponding neural responses. Many studies addressing this question vary the level of intelligibility by manipulating the acoustic waveform, but this makes it difficult to cleanly disentangle the effects of intelligibility from underlying acoustical confounds. Here, using magnetoencephalography recordings, we study neural measures of speech intelligibility by manipulating intelligibility while keeping the acoustics strictly unchanged. Acoustically identical degraded speech stimuli (three-band noise-vocoded, ~20 s duration) are presented twice, but the second presentation is preceded by the original (nondegraded) version of the speech. This intermediate priming, which generates a "pop-out" percept, substantially improves the intelligibility of the second degraded speech passage. We investigate how intelligibility and acoustical structure affect acoustic and linguistic neural representations using multivariate temporal response functions (mTRFs). As expected, behavioral results confirm that perceived speech clarity is improved by priming. mTRFs analysis reveals that auditory (speech envelope and envelope onset) neural representations are not affected by priming but only by the acoustics of the stimuli (bottom-up driven). Critically, our findings suggest that segmentation of sounds into words emerges with better speech intelligibility, and most strongly at the later (~400 ms latency) word processing stage, in prefrontal cortex, in line with engagement of top-down mechanisms associated with priming. Taken together, our results show that word representations may provide some objective measures of speech comprehension.

The Influence of Hearing Loss on the Pupil Response to Degraded Speech.

PURPOSE: Current evidence regarding the influence of hearing loss on the pupil response elicited by speech perception is inconsistent. This might be partially due to confounding effects of age. This study aimed to compare pupil responses in age-matched groups of normal-hearing (NH) and hard of hearing (HH) listeners during listening to speech. METHOD: We tested the baseline pupil size and mean and peak pupil dilation response of 17 NH participants (Mage = 46 years; age range: 20-62 years) and 17 HH participants (Mage = 45 years; age range: 20-63 years) who were pairwise matched on age and educational level. Participants performed three speech perception tasks at a 50% intelligibility level: noise-vocoded speech and speech masked with either stationary noise or interfering speech. They also listened to speech presented in quiet. RESULTS: Hearing loss was associated with poorer speech perception, except for noise-vocoded speech. In contrast to NH participants, performance of HH participants did not improve across trials for the interfering speech condition, and it decreased for speech in stationary noise. HH participants had a smaller mean pupil dilation in degraded speech conditions compared to NH participants, but not for speech in quiet. They also had a steeper decline in the baseline pupil size across trials. The baseline pupil size was smaller for noise-vocoded speech as compared to the other conditions. The normalized data showed an additional group effect on the baseline pupil response. CONCLUSIONS: Hearing loss is associated with a smaller pupil response and steeper decline in baseline pupil size during the perception of degraded speech. This suggests difficulties of the HH participants to sustain their effort investment and performance across the test session.

Clinical Assessment of Communication-Related Speech Parameters in Dysarthria: The Impact of Perceptual Adaptation.

PURPOSE: In current clinical practice, intelligibility of dysarthric speech is commonly assessed by speech-language therapists (SLTs), in most cases by the therapist caring for the patient being diagnosed. Since SLTs are familiar with dysarthria in general and with the speech of the individual patient to be assessed in particular, they have an adaptation advantage in understanding the patient's utterances. We examined whether and how listeners' assessments of communication-related speech parameters vary as a function of their familiarity with dysarthria in general and with the diagnosed patients in particular. METHOD: Intelligibility, speech naturalness, and perceived listener effort were assessed in 20 persons with dysarthria (PWD). Patients' speech samples were judged by the individual treating therapists, five dysarthria experts who were unfamiliar with the patients, and crowdsourced naïve listeners. Adaptation effects were analyzed using (a) linear mixed models of overall scoring levels, (b) regression models of severity dependence, (c) network analyses of between-listener and between-parameter relationships, and (d) measures of intra- and interobserver consistency. RESULTS: Significant advantages of dysarthria experts over laypeople were found in all parameters. An overall advantage of the treating therapists over nonfamiliar experts was only seen in listening effort. Severity-dependent adaptation effects occurred in all parameters. The therapists' responses were heterogeneous and inconsistent with those of the unfamiliar experts and the naïve listeners. CONCLUSIONS: The way SLTs evaluate communication-relevant speech parameters of the PWD whom they care for is influenced not only by adaptation benefits but also by therapeutic biases. This finding weakens the validity of assessments of communication-relevant speech parameters by the treating therapists themselves and encourages the development and use of alternative methods.

Long-term effects of subthalamic nucleus deep brain stimulation on speech in Parkinson's disease.

Bilateral subthalamic nucleus deep brain stimulation (STN-DBS) is an effective treatment in advanced Parkinson's Disease (PD). However, the effects of STN-DBS on speech are still debated, particularly in the long-term follow-up. The objective of this study was to evaluate the long-term effects of bilateral STN-DBS on speech in a cohort of advanced PD patients treated with bilateral STN-DBS. Each patient was assessed before surgery through a neurological evaluation and a perceptual-acoustic analysis of speech and re-assessed in the long-term in different stimulation and drug conditions. The primary outcome was the percentage change of speech intelligibility obtained by comparing the postoperative on-stimulation/off-medication condition with the preoperative off-medication condition. Twenty-five PD patients treated with bilateral STN-DBS with a 5-year follow-up were included. In the long-term, speech intelligibility stayed at the same level as preoperative values when compared with preoperative values. STN-DBS induced a significant acute improvement of speech intelligibility (p < 0.005) in the postoperative assessment when compared to the on-stimulation/off-medication and off-stimulation/off-medication conditions. These results highlight that STN-DBS may handle speech intelligibility even in the long-term.

The effects of speech masking on neural tracking of acoustic and semantic features of natural speech.

Listening environments contain background sounds that mask speech and lead to communication challenges. Sensitivity to slow acoustic fluctuations in speech can help segregate speech from background noise. Semantic context can also facilitate speech perception in noise, for example, by enabling prediction of upcoming words. However, not much is known about how different degrees of background masking affect the neural processing of acoustic and semantic features during naturalistic speech listening. In the current electroencephalography (EEG) study, participants listened to engaging, spoken stories masked at different levels of multi-talker babble to investigate how neural activity in response to acoustic and semantic features changes with acoustic challenges, and how such effects relate to speech intelligibility. The pattern of neural response amplitudes associated with both acoustic and semantic speech features across masking levels was U-shaped, such that amplitudes were largest for moderate masking levels. This U-shape may be due to increased attentional focus when speech comprehension is challenging, but manageable. The latency of the neural responses increased linearly with increasing background masking, and neural latency change associated with acoustic processing most closely mirrored the changes in speech intelligibility. Finally, tracking responses related to semantic dissimilarity remained robust until severe speech masking (-3 dB SNR). The current study reveals that neural responses to acoustic features are highly sensitive to background masking and decreasing speech intelligibility, whereas neural responses to semantic features are relatively robust, suggesting that individuals track the meaning of the story well even in moderate background sound.

Semantic Context Can Mask Intelligibility Declines at Above-Conversational Speech Levels in Normal-Hearing Listeners.

PURPOSE: While speech audibility generally improves with increasing level, declines in intelligibility are inconsistently observed at above-conversational levels, even in listeners with normal audiograms (NAs). The inconsistent findings could be due to different types of speech materials, ranging from monosyllabic words to everyday sentences, used across studies. Here, we hypothesized that semantic context can "mask" intelligibility declines at high levels by constraining plausible response options. METHOD: Intelligibility was assessed in speech-shaped noise with monosyllabic words, sentences without semantic context, and sentences with semantic context. Two presentation levels were used: 80 and 95 dB SPL broadband. Bandpass filtering was applied to minimize upward spread of masking. Twenty-two young adults with NAs were tested. RESULTS: Poorer performance at the higher level was found with the monosyllabic words and context-free sentences but not with the context-rich sentences. The scores obtained at the higher level with the two context-free materials were strongly correlated. The correlation was independent of the lower-level scores, suggesting that the high-level performance declines reflect "normal" auditory functioning. CONCLUSIONS: Young adults with NAs show intelligibility decreases at above-conversational levels when tested with speech materials without semantic context. Top-down processing as facilitated by context information can mask such declines.