Speech-modulated Noise Research Articles

Modulation Interference from Speech-Modulated Noise in Bimodal Cochlear Implant Users

Purpose: This study examined modulation interference in sentence recognition for bimodal cochlear implant (CI) users.Methods: Thirteen bimodal users and thirteen normal-hearing (NH) listeners (reference) participated in this study. The adaptive Korean Matrix sentence-in-noise test measured the speech reception thresholds (SRTs) required for 50% speech-in-noise intelligibility. As background noise, we presented two background noises: stationary speech-shaped noise (SSN) and single-talker speech-modulated masker (International Collegium of Rehabilitative Audiology noise, ICRA). The amount of masking release due to fluctuations in the speech-modulated noise, called speech masking release (SMR), was calculated from the difference between SRTs with SSN and SRTs with ICRA noise. The SRTs were measured twice for bimodal CI users: CI-only and bimodal listening.Results: The mean SMR for NH listeners was approximately 12 dB. The mean SMR for bimodal CI users was about -5 dB, with either CI alone or bimodal listening. This means that bimodal CI users experienced modulation interference rather than masking release from the temporal fluctuations. We observed positive bimodal benefits, yet the interference from fluctuating maskers was similar between the CI-only and bimodal listening. The low-frequency aided hearing thresholds in the non-implanted ear were unrelated to the amount of SMR for bimodal users.Conclusion: NH listeners could take advantage of temporal fluctuations in the speech-modulated noise. However, bimodal CI listeners hardly glimpsed target speech in the dips of the speech-modulated masker, regardless of listening mode. Bimodal listening did not significantly reduce modulation interference compared to CI-only listening.

Attenuation and distortion components of age-related hearing loss: Contributions to recognizing temporal-envelope filtered speech in modulated noise.

Older adults with hearing loss may experience difficulty recognizing speech in noise due to factors related to attenuation (e.g., reduced audibility and sensation levels, SLs) and distortion (e.g., reduced temporal fine structure, TFS, processing). Furthermore, speech recognition may improve when the amplitude modulation spectrum of the speech and masker are non-overlapping. The current study investigated this by filtering the amplitude modulation spectrum into different modulation rates for speech and speech-modulated noise. The modulation depth of the noise was manipulated to vary the SL of speech glimpses. Younger adults with normal hearing and older adults with normal or impaired hearing listened to natural speech or speech vocoded to degrade TFS cues. Control groups of younger adults were tested on all conditions with spectrally shaped speech and threshold matching noise, which reduced audibility to match that of the older hearing-impaired group. All groups benefitted from increased masker modulation depth and preservation of syllabic-rate speech modulations. Older adults with hearing loss had reduced speech recognition across all conditions. This was explained by factors related to attenuation, due to reduced SLs, and distortion, due to reduced TFS processing, which resulted in poorer auditory processing of speech cues during the dips of the masker.

Allocation of cognitive resources for older adults with normal or impaired hearing when listening to temporally degraded and masked speech

Hearing impairment may affect how older listeners allocate cognitive resources when communicating in challenging environments. Older adults with normal or impaired hearing completed three speech recognition studies. The studies consisted of 15-16 measures of temporally filtered speech with (1) degraded spectral cues, (2) competing speech-modulated noise, and (3) speech vocoding in speech-modulated noise. Generalization was assessed with measures of speech interruption, segregation, and multitalker masking. To account for audibility differences, all listeners received spectral shaping fit to their hearing thresholds. Measures in each study were reduced to a single principal component (PC) that represented speech recognition abilities. Participants also completed a cognitive test battery that yielded domain-specific PCs and a measure of speech glimpsing. For each study, hierarchical linear regression analysis was completed separately for subgroups of older adults with normal or impaired hearing using cognitive PCs as predictor variables, followed by speech glimpsing, age, and hearing thresholds. Vocabulary knowledge was the best predictor of speech recognition for older adults with normal hearing, whereas working memory consistently explained ∼30%-40% of the variance in recognition for older adults with hearing loss. Thus, even with sufficient audibility, hearing impairment may alter allocation of cognitive resources for older adults listening to degraded speech.

Recognition of spectrally shaped speech in speech-modulated noise: Effects of age, spectral shape, speech level, and vocoding.

This study examined the recognition of spectrally shaped syllables and sentences in speech-modulated noise by younger and older adults. The effect of spectral shaping and speech level on temporal amplitude modulation cues was explored through speech vocoding. Subclinical differences in hearing thresholds in older adults were controlled using threshold matching noise. Older, compared to younger, adults had poorer recognition but similar improvements as the bandwidth of the shaping function increased. Spectral shaping may enhance the sensation level of glimpsed speech, which improves speech recognition in noise, even with mild elevations in hearing thresholds.

The Influence of Noise Type and Semantic Predictability on Word Recall in Older Listeners and Listeners With Hearing Impairment.

A dual-task paradigm was implemented to investigate how noise type and sentence context may interact with age and hearing loss to impact word recall during speech recognition. Three noise types with varying degrees of temporal/spectrotemporal modulation were used: speech-shaped noise, speech-modulated noise, and three-talker babble. Participant groups included younger listeners with normal hearing (NH), older listeners with near-normal hearing, and older listeners with sensorineural hearing loss. An adaptive measure was used to establish the signal-to-noise ratio approximating 70% sentence recognition for each participant in each noise type. A word-recall task was then implemented while matching speech-recognition performance across noise types and participant groups. Random-intercept linear mixed-effects models were used to determine the effects of and interactions between noise type, sentence context, and participant group on word recall. The results suggest that noise type does not significantly impact word recall when word-recognition performance is controlled. When data from noise types were pooled and compared with quiet, and recall was assessed: older listeners with near-normal hearing performed well when either quiet backgrounds or high sentence context (or both) were present, but older listeners with hearing loss performed well only when both quiet backgrounds and high sentence context were present. Younger listeners with NH were robust to the detrimental effects of noise and low context. The general presence of noise has the potential to decrease word recall, but type of noise does not appear to significantly impact this observation when overall task difficulty is controlled. The presence of noise as well as deficits related to age and/or hearing loss appear to limit the availability of cognitive processing resources available for working memory during conversation in difficult listening environments. The conversation environments that impact these resources appear to differ depending on age and/or hearing status.

Glimpsing keywords across sentences in noise: A microstructural analysis of acoustic, lexical, and listener factors.

This study investigated how acoustic and lexical word-level factors and listener-level factors of auditory thresholds and cognitive-linguistic processing contribute to the microstructure of sentence recognition in unmodulated and speech-modulated noise. The modulation depth of the modulated masker was changed by expanding and compressing the temporal envelope to control glimpsing opportunities. Younger adults with normal hearing (YNH) and older adults with normal and impaired hearing were tested. A second group of YNH was tested under acoustically identical conditions to the hearing-impaired group, who received spectral shaping. For all of the groups, speech recognition declined and masking release increased for later keywords in the sentence, which is consistent with the word position decreases in the signal-to-noise ratio. The acoustic glimpse proportion and lexical word frequency of individual keywords predicted recognition under different noise conditions. For the older adults, better auditory thresholds and better working memory abilities facilitated sentence recognition. Vocabulary knowledge contributed more to sentence recognition for younger than for older adults. These results demonstrate that acoustic and lexical factors contribute to the recognition of individual words within a sentence, but relative contributions vary based on the noise modulation characteristics. Taken together, acoustic, lexical, and listener factors contribute to how individuals recognize keywords during sentences.

Comparing Speech Recognition for Listeners With Normal and Impaired Hearing: Simulations for Controlling Differences in Speech Levels and Spectral Shape.

Purpose This study investigated methods used to simulate factors associated with reduced audibility, increased speech levels, and spectral shaping for aided older adults with hearing loss. Simulations provided to younger normal-hearing adults were used to investigate the effect of sensation level, speech presentation level, and spectral shape in comparison to older adults with hearing loss. Method Measures were assessed in quiet, steady-state noise, and speech-modulated noise. Older adults with hearing loss listened to speech that was spectrally shaped according to their hearing thresholds. Younger adults with normal hearing listened to speech that simulated the hearing-impaired group's (a) reduced audibility, (b) increased speech levels, and (c) spectral shaping. Group comparisons were made based on speech recognition performance and masking release. Additionally, younger adults completed measures of listening effort and perceived speech quality to assess if differences across simulations in these outcome measures were similar to those for speech recognition. Results Across the various simulations employed, testing in the presence of a threshold matching noise best matched differences in speech recognition and masking release between younger and older adults. This result remained consistent across the other two outcome measures. Conclusions A combination of audibility, speech level, and spectral shape factors is required to simulate differences between listeners with normal and impaired hearing in recognition, listening effort, and perceived speech quality. The use of spectrally shaped and amplified speech in the presence of threshold matching noise best provided this simulated control. Supplemental Material https://doi.org/10.23641/asha.13224632.

Assessing the benefit of acoustic beamforming for listeners with aphasia using modified psychoacoustic methods.

Acoustic beamforming has been shown to improve identification of target speech in noisy listening environments for individuals with sensorineural hearing loss. This study examined whether beamforming would provide a similar benefit for individuals with aphasia (acquired neurological language impairment). The benefit of beamforming was examined for persons with aphasia (PWA) and age- and hearing-matched controls in both a speech masking condition and a speech-shaped, speech-modulated noise masking condition. Performance was measured when natural spatial cues were provided, as well as when the target speech level was enhanced via a single-channel beamformer. Because typical psychoacoustic methods may present substantial experimental confounds for PWA, clinically guided modifications of experimental procedures were determined individually for each PWA participant. Results indicated that the beamformer provided a significant overall benefit to listeners. On an individual level, both PWA and controls who exhibited poorer performance on the speech masking condition with spatial cues benefited from the beamformer, while those who achieved better performance with spatial cues did not. All participants benefited from the beamformer in the noise masking condition. The findings suggest that a spatially tuned hearing aid may be beneficial for older listeners with relatively mild hearing loss who have difficulty taking advantage of spatial cues.

High-frequency spectral shaping enhances glimpsing speech in noise for younger adults with normal hearing

Amplification is necessary to restore audibility to individuals with hearing impairment. However, frequency-specific amplification alters the spectrum of speech in addition to increasing the speech level. The current study investigated the effects of spectrum and speech level on speech recognition by younger adults with normal hearing. Sentence recognition was measured in quiet, speech-modulated noise, and steady-state noise. In addition, acoustic metrics were utilized to quantify the alterations resulting from spectral shaping. Acoustic metrics included (1) the Hearing Aid Speech Perception Index, in order to investigate changes to the temporal envelope, and (2) glimpse analyses, to quantify the proportion of time-frequency units that were glimpsed in a sentence. Results demonstrated that at high speech levels in quiet, spectral shaping was associated with lower sentence recognition. However, in all other conditions, and particularly in noise, spectral shaping enhanced sentence recognition. Acoustic metrics indicated that this enhancement in noise is associated with increases in the proportion and signal-to-noise ratio of glimpses, which resulted in improved preservation of the envelope and temporal fine structure of sentences in comparison to unshaped stimuli. Thus, spectral shaping is beneficial for speech recognition in noise for normal hearing participants due to enhanced speech glimpses.

Minimal and Mild Hearing Loss in Children: Association with Auditory Perception, Cognition, and Communication Problems.

"Minimal" and "mild" hearing loss are the most common but least understood forms of hearing loss in children. Children with better ear hearing level as low as 30 dB HL have a global language impairment and, according to the World Health Organization, a "disabling level of hearing loss." We examined in a population of 6- to 11-year-olds how hearing level ≤40.0 dB HL (1 and 4 kHz pure-tone average, PTA, threshold) is related to auditory perception, cognition, and communication. School children (n = 1638) were recruited in 4 centers across the United Kingdom. They completed a battery of hearing (audiometry, filter width, temporal envelope, speech-in-noise) and cognitive (IQ, attention, verbal memory, receptive language, reading) tests. Caregivers assessed their children's communication and listening skills. Children included in this study (702 male; 752 female) had 4 reliable tone thresholds (1, 4 kHz each ear), and no caregiver reported medical or intellectual disorder. Normal-hearing children (n = 1124, 77.1%) had all 4 thresholds and PTA <15 dB HL. Children with ≥15 dB HL for at least 1 threshold, and PTA <20 dB (n = 245, 16.8%) had minimal hearing loss. Children with 20 ≤PTA <40 dB HL (n = 88, 6.0%) had mild hearing loss. Interaural asymmetric hearing loss ( left PTA - right PTA ≥10 dB) was found in 28.9% of those with minimal and 39.8% of those with mild hearing loss. Speech perception in noise, indexed by vowel-consonant-vowel pseudoword repetition in speech-modulated noise, was impaired in children with minimal and mild hearing loss, relative to normal-hearing children. Effect size was largest (d = 0.63) in asymmetric mild hearing loss and smallest (d = 0.21) in symmetric minimal hearing loss. Spectral (filter width) and temporal (backward masking) perceptions were impaired in children with both forms of hearing loss, but suprathreshold perception generally related only weakly to PTA. Speech-in-noise (nonsense syllables) and language (pseudoword repetition) were also impaired in both forms of hearing loss and correlated more strongly with PTA. Children with mild hearing loss were additionally impaired in working memory (digit span) and reading, and generally performed more poorly than those with minimal loss. Asymmetric hearing loss produced as much impairment overall on both auditory and cognitive tasks as symmetric hearing loss. Nonverbal IQ, attention, and caregiver-rated listening and communication were not significantly impaired in children with hearing loss. Modeling suggested that 15 dB HL is objectively an appropriate lower audibility limit for diagnosis of hearing loss. Hearing loss between 15 and 30 dB PTA is, at ~20%, much more prevalent in 6- to 11-year-old children than most current estimates. Key aspects of auditory and cognitive skills are impaired in both symmetric and asymmetric minimal and mild hearing loss. Hearing loss <30 dB HL is most closely related to speech perception in noise, and to cognitive abilities underpinning language and reading. The results suggest wider use of speech-in-noise measures to diagnose and assess management of hearing loss and reduction of the clinical hearing loss threshold for children to 15 dB HL.

Changes in Speech-Related Brain Activity During Adaptation to Electro-Acoustic Hearing.

Objectives: Hearing improves significantly with bimodal provision, i.e., a cochlear implant (CI) at one ear and a hearing aid (HA) at the other, but performance shows a high degree of variability resulting in substantial uncertainty about the performance that can be expected by the individual CI user. The objective of this study was to explore how auditory event-related potentials (AERPs) of bimodal listeners in response to spoken words approximate the electrophysiological response of normal hearing (NH) listeners.Study Design: Explorative prospective analysis during the first 6 months of bimodal listening using a within-subject repeated measures design.Setting: Academic tertiary care center.Participants: Twenty-seven adult participants with bilateral sensorineural hearing loss who received a HiRes 90K CI and continued use of a HA at the non-implanted ear. Age-matched NH listeners served as controls.Intervention: Cochlear implantation.Main Outcome Measures: Obligatory auditory evoked potentials N1 and P2, and the event-related N2 potential in response to monosyllabic words and their reversed sound traces before, as well as 3 and 6 months post-implantation. The task required word/non-word classification. Stimuli were presented within speech-modulated noise. Loudness of word/non-word signals was adjusted individually to achieve the same intelligibility across groups and assessments.Results: Intelligibility improved significantly with bimodal hearing, and the N1–P2 response approximated the morphology seen in NH with enhanced and earlier responses to the words compared to their reversals. For bimodal listeners, a prominent negative deflection was present between 370 and 570 ms post stimulus onset (N2), irrespective of stimulus type. This was absent for NH controls; hence, this response did not approximate the NH response during the study interval. N2 source localization evidenced extended activation of general cognitive areas in frontal and prefrontal brain areas in the CI group.Conclusions: Prolonged and spatially extended processing in bimodal CI users suggests employment of additional auditory–cognitive mechanisms during speech processing. This does not reduce within 6 months of bimodal experience and may be a correlate of the enhanced listening effort described by CI listeners.

Illusory Conjunctions in Speech Perception as a Lens into the Characteristics of Hearing Loss

This study explores the formation of a complex illusory conjunction in simulated speech perception that has yet to see a parallel in visual cognition. The illusory conjunction dealt with in this paper is confounded by 2 disparate spatial modalities – a) spatialization of competing formant features across high and low frequency bands on one hand and b) high-level expectation of speech content competing with the low level processing of auditory objects (such as speechmodulated noise). This paper has extended on a previous initial study around this topic, by controlling for the illusory conjunctions in one of the spatial dimensions (formant space) to then account for specific individual differences as possible correlations with individual hearing abilities across the audible frequency range. The results are an encouraging direction towards a better understanding of audition through the controlled perception of illusory conjunctions.

Effects of age, modulation rate, and modulation depth on sentence recognition in speech-modulated noise

Speech is often heard in amplitude modulated backgrounds when speech is glimpsed during momentary masker dips. Increased masker modulation depth provides more improvement in the signal-to-noise ratio of glimpsed speech, but also improves noise modulation detection for potentially greater modulation masking. Mechanisms of modulation masking and glimpsing may also depend on the overlap of the modulation spectra of the speech and noise. This study employed modulation filtering and noise amplitude compression to investigate the combined effects of noise modulation depth and modulation rate on speech recognition. Younger normal-hearing (YNH), older normal-hearing (ONH), and older hearing-impaired (OHI) adults listened to sentences in noise that were spectrally shaped to control for individual hearing thresholds. A second YNH group listened to sentences with the same spectral shaping as OHI listeners. Sentence recognition generally improved with greater noise modulation depth, especially at higher modulation rates. Results suggest that speech recognition for all groups is maximized when speech modulations &amp;lt;8 Hz are preserved, when noise modulation occurs at rates higher than this range, and with greater noise modulation depth. OHI listeners benefit similarly from these conditions, but their poorer overall performance may be due to reduced sensation levels. [Work supported by NIH/NIDCD.]

Patient Benefit Following Bimodal CI-provision: Self-reported Abilities vs. Hearing Status.

Objectives: Patient-reported outcomes gain importance for the assessment of auditory abilities in cochlear implant users and for the evaluation of auditory rehabilitation. Aims of the study were to explore the interrelation of self-reported improvements in auditory ability with improvements in speech comprehension and to identify factors other than audiological improvement that affect self-reported auditory ability.Study Design: Explorative prospective analysis using a within-subjects repeated measures design.Setting: Academic tertiary care center.Participants: Twenty-seven adult participants with bilateral sensorineural hearing loss who received a HiRes 90K CI and continued use of a HA at the non-implanted ear (bimodal hearing).Intervention: Cochlear implantation.Main Outcome Measures: Self-reported auditory ability/disability assessed by the comparative version of the Speech, Spatial and Qualities of Hearing Scale (SSQ-B), and monosyllable as well as sentence comprehension in quiet and within speech modulated noise from different directions assessed pre- as well as 3 and 6 months post-implantation.Results: Data of 17 individuals were analyzed. At the endpoint of the study, improvement of self-reported auditory ability was significant. Regarding audiometric measures, significant improvement was seen for CI-aided pure tone thresholds, for monaural CI-assisted and bimodal sentence comprehension in quiet and in speech-modulated noise that was presented from the same source or at the side of the HA-ear. Correlations between self-reported and audiometric improvements remained weak, with the exception of the improvement seen for monaural CI-aided sentence comprehension in quiet and self-perceived improvement of sound quality. Considerable correlations existed between self-reported improvements and current level of depression and anxiety, and with general self-efficaciousness. Regression analyses substantiated a positive influence of self-efficaciousness on self-reported improvement in speech comprehension and between the improvement of monaural CI-aided sentence comprehension in quiet and perceived sound quality as well as a negative influence of anxiety on self-reported improvement in spatial hearing. Self-reported improvements were significantly better in the subgroup with intensive as compared to regular rehabilitation.Conclusions: Self-reported auditory ability/disability represents an important measure for the success of bimodal CI-provision. It is influenced by personal and mental health factors that may improve CI-rehabilitation results if addressed during rehabilitation.

Glimpsing speech interrupted by speech-modulated noise

Everyday environments frequently present speech in modulated noise backgrounds, such as from a competing talker. Under such conditions, temporal glimpses of speech may be preserved at favorable signal-to-noise ratios during the amplitude dips of the masker. Speech recognition is determined, in part, by these speech glimpses. However, properties of the noise when it dominates the speech may also be important. This study interrupted speech to provide either high-intensity or low-intensity speech glimpses derived from measurements of speech-on-speech masking. These interrupted intervals were deleted and subsequently filled by steady-state noise or one of four different types of noise amplitude modulated by the same or different sentence. Noise was presented at two different levels. Interruption by silence was also examined. Speech recognition was best with high-intensity glimpses and improved when the noise was modulated by missing high-intensity segments. Additional noise conditions detailed significant interactions between the noise level and glimpsed speech level. Overall, high-intensity speech segments, and the amplitude modulation (AM) of the segments, are crucial for speech recognition. Speech recognition is further influenced by the properties of the competing noise (i.e., level and AM) which interact with the glimpsed speech level. Acoustic properties of both speech-dominated and noise-dominated intervals of speech-noise mixtures determine speech recognition.

Binaural speech unmasking and interference in adult bilateral cochlear-implant users

Bilateral cochlear implants (BICIs) provide improved speech perception in noise, primarily derived from the head-shadow benefit. BICI listeners can also demonstrate binaural speech unmasking or squelch, particularly if the interferer is a single other speaker. However, under the same conditions, some BICI listeners can experience interference. This study tested 21 adult BICI listeners on speech understanding using a range of masker conditions (1, 2, 3, or 4 same-sex talkers, speech-modulated noise, or speech-shaped stationary noise). For listeners that showed binaural unmasking, the amount of unmasking was highest for the one-talker condition and least for the stationary noise, decreasing as the number of interfering talkers increased and the envelope modulation depth decreased. For listeners that showed interference, there were mainly two types of interference patterns: (1) where the amount of interference varied idiosyncratically across masker type, and (2) any stimulation in one ear essentially produced chance performance in the other ear for all masker conditions. The latter interference pattern occurred for the listeners with the largest asymmetries in speech understanding. This suggests, in these extreme cases, a possible central cortical processing bias for one ear and a more equal speech understanding between the ears may diminish interference.

Assessing cognitive and perceptual abilities by manipulating task requirements when listening to speech in noise

Speech recognition involves both cognitive and perceptual processing that can be differentially affected by the task requirements. This study assessed the degree to which different cognitive and perceptual abilities explained speech recognition using the Coordinate Response Measure (CRM). Speech recognition was assessed by varying the requirements of attention (i.e., selective or divided attention), and by assessing perceptual processes related to speech glimpsing (i.e., steady-state noise versus speech-modulated noise). Additional cognitive and perceptual tasks assessed cognitive interference, working memory, and amplitude modulation detection at 4 and 10 Hz. Results demonstrated that masking release (was most associated with modulation detection, indicating that the ability to take advantage of momentary dips in the masker (i.e., glimpsing) requires better amplitude modulation detection abilities. In contrast, when attentional constraints were imposed, a measure of cognitive interference was most predictive of performance for reporting keywords spoken by both the target talker (i.e., accurate responses) and competitor (i.e., intrusion responses). Interestingly, our measure of working memory was not correlated with any of the CRM tasks. These results suggest that conditions in which the CRM task is administered (i.e. manipulating noise or attention) can differentially weight separate perceptual and cognitive skills. [Work supported, in part, by NIH/NIDCD.]Speech recognition involves both cognitive and perceptual processing that can be differentially affected by the task requirements. This study assessed the degree to which different cognitive and perceptual abilities explained speech recognition using the Coordinate Response Measure (CRM). Speech recognition was assessed by varying the requirements of attention (i.e., selective or divided attention), and by assessing perceptual processes related to speech glimpsing (i.e., steady-state noise versus speech-modulated noise). Additional cognitive and perceptual tasks assessed cognitive interference, working memory, and amplitude modulation detection at 4 and 10 Hz. Results demonstrated that masking release (was most associated with modulation detection, indicating that the ability to take advantage of momentary dips in the masker (i.e., glimpsing) requires better amplitude modulation detection abilities. In contrast, when attentional constraints were imposed, a measure of cognitive interference was most predic...

Lombard Effect in Polish Speech and its Comparison in English Speech

Abstract The first extensive investigation on the Lombard effect with Polish speech has been performed. Characteristic parameters of Lombard speech were measured: intensity, fundamental frequency, spectral tilt, duration of words, duration of pauses and duration of vowels. The effect was investigated in a task involving real communication - solving a Sudoku puzzle. The speakers produced speech in quiet and in three different backgrounds: competing speech, speech-shaped noise and speech-modulated noise. The experimental conditions were held as close as possible to those in the study by Cooke and Lu (2010) so that conclusions could be drawn whether differences between the Lombard effect in Polish speech and English speech existed. Most of the findings on the Lombard effect known from the literature have been confirmed with Polish speech. In three parameters, Polish speakers were more sensitive to modulated backgrounds while English speakers were more sensitive to a stationary background. In both languages, the modulated backgrounds induced speakers to extend pauses in the communication tasks.

The independent contribution of glimpse properties to speech recognition in speech-modulated noise

During fluctuating noise, temporal speech fragments (i.e., glimpses) at sufficient signal-to-noise ratios (SNRs) contribute to speech recognition. Different acoustic properties of these glimpses, related to rate and proportion, reflect the temporal distribution of available speech cues. Glimpse metrics may be used to define different aspects of this temporal distribution. However, these measures are often highly correlated, limiting interpretation of how different glimpse properties contribute independently to speech recognition. The present study investigates how the local SNR cutoff (LC) influences the correlation between glimpse metrics and affects related associations with speech recognition. Speech recognition was assessed in the presence of speech-modulated noise that was temporally manipulated through time compression and presented at different SNRs. Optimization analyses identified LCs that yielded glimpse metrics that were most correlated with the perceptual data. Stimulus manipulations of the noise modulation spectrum and noise level were most related to changes in the glimpse rate and proportion of glimpsed speech, respectively. At an LC of -2 dB, the correlation between these glimpse parameters was minimized while the combined association with speech recognition performance was maximized. Results suggest two glimpse mechanisms, with the relative importance of either mechanism determined by the acoustic noise properties and the analyzed LC.

Amplitude-modulation detection and speech recognition in normal and hearing-impaired listeners

Even though temporal speech envelopes may form a salient cue when listening to speech in noisy backgrounds, the relationship between speech intelligibility and the sensitivity to detecting temporal envelopes (i.e., amplitude modulation detection) is not well understood. This study measured speech reception thresholds in quiet, stationary and speech-modulated noise in three listener groups: young (yNH) and older normal-hearing (oNH) listeners and hearing-impaired (HI) listeners. In addition to broadband speech and noise signals, we adopted low and high-pass filtered versions of the stimuli to study the contribution of different coding mechanisms in basal and apical cochlear regions. For the same listeners, amplitude-modulation (AM) detection thresholds were measured in quiet and in the presence of broadband masking noise for 70 dB AM tones of 0.5, 2 and 4 kHz with either 100 or 5 Hz modulation frequency. Even though group trends were clearer than individual differences, AM detection thresholds showed a relationship to speech recognition in the low-pass filtered speech-modulated noise condition, and for yNH and oNH listeners in the high-pass filtered condition. Overall, this study sheds light on the importance of temporal envelope coding sensitivity for speech recognition and its relationship to near-and supra-threshold hearing deficits.