Measured Speech Reception Thresholds Research Articles

A Randomized Crossover Study in Single-Sided Deafness Comparing a Cartilage Conduction CROS System and an Air-Conduction CROS System.

To investigate if cartilage conduction (CC) rerouting devices are noninferior to air-conduction (AC) rerouting devices for single-sided deafness (SSD) patients by measuring objective and subjective performance using speech-in-noise tests that resemble a realistic hearing environment, sound localization tests, and standardized questionnaires. Prospective, single-subject randomized, crossover study. Anechoic room inside a university. Nine adults between 21 and 58 years of age with severe or profound unilateral sensorineural hearing loss. Patients' baseline hearing was assessed; they then used both the cartilage conduction contralateral routing of signals device (CC-CROS) and an air-conduction CROS hearing aid (AC-CROS). Patients wore each device for 2 weeks in a randomly assigned order. Three main outcome measures were 1) speech-in-noise tests, measuring speech reception thresholds; 2) proportion of correct sound localization responses; and 3) scores on the questionnaires, "Abbreviated Profile of Hearing Aid Benefit" (APHAB) and "Speech, Spatial, and Qualities of Hearing Scale" with 12 questions (SSQ-12). Speech reception threshold improved significantly when noise was ambient, and speech was presented from the front or the poor-ear side with both CC-CROS and AC-CROS. When speech was delivered from the better-ear side, AC-CROS significantly improved performance, whereas CC-CROS had no significant effect. Both devices mainly worsened sound localization, whereas the APHAB and SSQ-12 scores showed benefits. CC-CROS has noninferior hearing-in-noise performance except when the speech was presented to the better ear under ambient noise. Subjective measures showed that the patients realized the effectiveness of both devices.

Masked Speech Perception with Bone Conduction Device, Contralateral Routing of Signals Hearing Aid, and Cochlear Implant Use in Adults with Single-Sided Deafness: A Prospective Hearing Device Comparison using a Unified Testing Framework

Introduction: For the treatment of single-sided deafness (SSD), common treatment choices include a contralateral routing of signals (CROS) hearing aid, a bone conduction device (BCD), and a cochlear implant (CI). The primary aim of this study was to compare speech understanding in noise and binaural benefits in adults with postlingual SSD between preoperative unaided baseline, preoperative CROS and BCD trial devices, and CI, following recommendations from a consensus protocol. In addition, we investigated the effect of masker type on speech understanding. Methods: This was a prospective study with twelve participants. Binaural effects of head shadow, squelch, summation, and spatial release from masking were assessed by measuring speech reception thresholds (SRTs) in five different spatial target-masker configurations using two different maskers: two-talker babble (TTB), and speech-shaped noise (SSN). Preoperatively, participants were assessed unaided and with CROS and BCD trial devices. After cochlear implantation, participants were assessed at 1, 3, and 6 months post-activation. Results: For TTB, significant improvements in SRT with a CI relative to preoperatively unaided were found in all spatial configurations. With CI at 6 months, median benefits were 7.8 dB in S_SSDN_AH and 5.1 dB in S₀N_AH (head shadow), 3.4 dB in S₀N₀ (summation), and 4.6 dB in S₀N_SSD and 5.1 dB in S_AHN_SSD (squelch). CROS yielded a significant head shadow benefit of 2.4 dB in S_SSDN_AH and a significant deterioration in squelch of 2.5 dB in S₀N_SSD and S_AHN_SSD, but no summation effect. With BCD, there was a significant summation benefit of 1.5 dB, but no head shadow nor squelch effect. For SSN, significant improvements in SRT with CI compared to preoperatively unaided were found in three spatial configurations. Median benefits with CI at 6 months were: 8.5 dB in S_SSDN_AH and 4.6 dB in S₀N_AH (head shadow), 1.4 dB in S₀N₀ (summation), but no squelch. CROS showed a significant head shadow benefit of 1.7 dB in S_SSDN_AH, but no summation effect, and a significant deterioration in squelch of 2.9 dB in S₀N_SSD and 3.2 dB in S_AHN_SSD. With BCD, no binaural effect was obtained. Longitudinally, we found significant head shadow benefits with a CI in S_SSDN_AH in both maskers at all postoperative intervals and in S₀N_AH at 3 and 6 months post-activation. Conclusion: With a CI, a clear benefit for masked speech perception was observed for all binaural effects. Benefits with CROS and BCD were more limited. CROS usage was detrimental to the squelch effect.

The Relative Contribution of Cochlear Synaptopathy and Reduced Inhibition to Age-Related Hearing Impairment for People With Normal Audiograms.

Older people often show auditory temporal processing deficits and speech-in-noise intelligibility difficulties even when their audiogram is clinically normal. The causes of such problems remain unclear. Some studies have suggested that for people with normal audiograms, age-related hearing impairments may be due to a cognitive decline, while others have suggested that they may be caused by cochlear synaptopathy. Here, we explore an alternative hypothesis, namely that age-related hearing deficits are associated with decreased inhibition. For human adults (N = 30) selected to cover a reasonably wide age range (25-59 years), with normal audiograms and normal cognitive function, we measured speech reception thresholds in noise (SRTNs) for disyllabic words, gap detection thresholds (GDTs), and frequency modulation detection thresholds (FMDTs). We also measured the rate of growth (slope) of auditory brainstem response wave-I amplitude with increasing level as an indirect indicator of cochlear synaptopathy, and the interference inhibition score in the Stroop color and word test (SCWT) as a proxy for inhibition. As expected, performance in the auditory tasks worsened (SRTNs, GDTs, and FMDTs increased), and wave-I slope and SCWT inhibition scores decreased with ageing. Importantly, SRTNs, GDTs, and FMDTs were not related to wave-I slope but worsened with decreasing SCWT inhibition. Furthermore, after partialling out the effect of SCWT inhibition, age was no longer related to SRTNs or GDTs and became less strongly related to FMDTs. Altogether, results suggest that for people with normal audiograms, age-related deficits in auditory temporal processing and speech-in-noise intelligibility are mediated by decreased inhibition rather than cochlear synaptopathy.

The Genetic contribution to solving the cocktail-party problem

SummaryCommunicating in everyday situations requires solving the cocktail-party problem, or segregating the acoustic mixture into its constituent sounds and attending to those of most interest. Humans show dramatic variation in this ability, leading some to experience real-world problems irrespective of whether they meet criteria for clinical hearing loss. Here, we estimated the genetic contribution to cocktail-party listening by measuring speech-reception thresholds (SRTs) in 425 people from large families and ranging in age from 18 to 91 years. Roughly half the variance of SRTs was explained by genes (h2 = 0.567). The genetic correlation between SRTs and hearing thresholds (HTs) was medium (ρG = 0.392), suggesting that the genetic factors influencing cocktail-party listening were partially distinct from those influencing sound sensitivity. Aging and socioeconomic status also strongly influenced SRTs. These findings may represent a first step toward identifying genes for “hidden hearing loss,” or hearing problems in people with normal HTs.

Investigating the role of harmonic cancellation in speech-on-speech masking

This study investigated the role of harmonic cancellation in the intelligibility of speech in “cocktail party” situations. While there is evidence that harmonic cancellation plays a role in the segregation of simple harmonic sounds based on fundamental frequency (F0), its utility for mixtures of speech containing non-stationary F0s and unvoiced segments is unclear. Here we focused on the energetic masking of speech targets caused by competing speech maskers. Speech reception thresholds were measured using seven maskers: speech-shaped noise, monotonized and intonated harmonic complexes, monotonized speech, noise-vocoded speech, reversed speech and natural speech. These maskers enabled an estimate of how the masking potential of speech is influenced by harmonic structure, amplitude modulation and variations in F0 over time. Measured speech reception thresholds were compared to the predictions of two computational models, with and without a harmonic cancellation component. Overall, the results suggest a minor role of harmonic cancellation in reducing energetic masking in speech mixtures.

Controlled (re)evaluation of the relationship between speech perception in noise and contralateral suppression of otoacoustic emissions

In people with normal hearing (NH), speech perception in noise (SPIN) improves when the speech signal is presented not gated with noise but after a delay. The medial olivocochlear reflex (MOCR) was thought to be involved in the neural dynamic range adaptation (NDRA) responsible for this adaptive SPIN; however, some of the recent studies do not support this hypothesis and suggest that adaptive SPIN involves the NDRA to noise-level statistics, irrespective of MOCR activation. A plausible reason for this discrepancy could be the variations and limitations of the experimental designs used in different studies. Using a relatively controlled and comprehensive study design, this study attempts to verify whether a delay between the delivery of speech and the noise improves the SPIN and whether MOCR mediates such effects. The SPIN was estimated by measuring speech reception thresholds (SRT) in noise under simultaneous-onset and delayed-onset (noise precedes speech onset by 300 ms) conditions. The SPIN in both ears was independently examined for ipsilateral, contralateral, and bilateral noise in women with normal hearing (N = 18; age range, 18–25 years). Contralateral suppression of transient-evoked otoacoustic emissions (CSOAEs) was used to estimate the MOCR based cochlear gain reduction. Under all test conditions, SPIN was improved in delayed-onset than in simultaneous-onset conditions, and the mean improvement in the SRT ranged from 0.7±1.7 to 1.8±1.8 dB. No significant correlation was obtained between CSOAEs and the mean temporal improvement in SRT, suggesting that MOCR may not be a predominant mechanism for the temporal improvement in SPIN.

Older Listeners' Perception of Speech With Strengthened and Weakened Dynamic Pitch Cues in Background Noise

Purpose Dynamic pitch, which is defined as the variation in fundamental frequency, is an acoustic cue that aids speech perception in noise. This study examined the effects of strengthened and weakened dynamic pitch cues on older listeners' speech perception in noise, as well as how these effects were modulated by individual factors including spectral perception ability. Method The experiment measured speech reception thresholds in noise in both younger listeners with normal hearing and older listeners whose hearing status ranged from near-normal hearing to mild-to-moderate sensorineural hearing loss. The pitch contours of the target speech were manipulated to create four levels of dynamic pitch strength: weakened, original, mildly strengthened, and strengthened. Listeners' spectral perception ability was measured using tests of spectral ripple and frequency modulation discrimination. Results Both younger and older listeners performed worse with manipulated dynamic pitch cues than with original dynamic pitch. The effects of dynamic pitch on older listeners' speech recognition were associated with their age but not with their perception of spectral information. Those older listeners who were relatively younger were more negatively affected by dynamic pitch manipulations. Conclusions The findings suggest the current pitch manipulation strategy is detrimental for older listeners to perceive speech in noise, as compared to original dynamic pitch. While the influence of age on the effects of dynamic pitch is likely due to age-related declines in pitch perception, the spectral measures used in this study were not strong predictors for dynamic pitch effects. Taken together, these results indicate next steps in this line of work should be focused on how to manipulate acoustic cues in speech in order to improve speech perception in noise for older listeners.

Using Spectral Blurring to Assess Effects of Channel Interaction on Speech-in-Noise Perception with Cochlear Implants

Cochlear implant (CI) listeners struggle to understand speech in background noise. Interactions between electrode channels due to current spread increase the masking of speech by noise and lead to difficulties with speech perception. Strategies that reduce channel interaction therefore have the potential to improve speech-in-noise perception by CI listeners, but previous results have been mixed. We investigated the effects of channel interaction on speech-in-noise perception and its association with spectro-temporal acuity in a listening study with 12 experienced CI users. Instead of attempting to reduce channel interaction, we introduced spectral blurring to simulate some of the effects of channel interaction by adjusting the overlap between electrode channels at the input level of the analysis filters or at the output by using several simultaneously stimulated electrodes per channel. We measured speech reception thresholds in noise as a function of the amount of blurring applied to either all 15 electrode channels or to 5 evenly spaced channels. Performance remained roughly constant as the amount of blurring applied to all channels increased up to some knee point, above which it deteriorated. This knee point differed across listeners in a way that correlated with performance on a non-speech spectro-temporal task, and is proposed here as an individual measure of channel interaction. Surprisingly, even extreme amounts of blurring applied to 5 channels did not affect performance. The effects on speech perception in noise were similar for blurring at the input and at the output of the CI. The results are in line with the assumption that experienced CI users can make use of a limited number of effective channels of information and tolerate some deviations from their everyday settings when identifying speech in the presence of a masker. Furthermore, these findings may explain the mixed results by strategies that optimized or deactivated a small number of electrodes evenly distributed along the array by showing that blurring or deactivating one-third of the electrodes did not harm speech-in-noise performance.

Segmentation of binaural room impulse responses for speech intelligibility prediction.

The two most important aspects in binaural speech perception-better-ear-listening and spatial-release-from-masking-can be predicted well with current binaural modeling frameworks operating on head-related impulse responses, i.e., anechoic binaural signals. To incorporate effects of reverberation, a model extension was proposed, splitting binaural room impulse responses into an early, useful, and late, detrimental part, before being fed into the modeling framework. More recently, an interaction between the applied splitting time, room properties, and the resulting prediction accuracy was observed. This interaction was investigated here by measuring speech reception thresholds (SRTs) in quiet with 18 normal-hearing subjects for four simulated rooms with different reverberation times and a constant room geometry. The mean error with one of the most promising binaural prediction models could be reduced by about 1 dB by adapting the applied splitting time to room acoustic parameters. This improvement in prediction accuracy can make up a difference of 17% in absolute intelligibility within the applied SRT measurement paradigm.

Speech Recognition Abilities in Normal-Hearing Children 4 to 12 Years of Age in Stationary and Interrupted Noise

Objectives:The main purpose of this study was to examine developmental effects for speech recognition in noise abilities for normal-hearing children in several listening conditions, relevant for daily life. Our aim was to study the auditory component in these listening abilities by using a test that was designed to minimize the dependency on nonauditory factors, the digits-in-noise (DIN) test. Secondary aims were to examine the feasibility of the DIN test for children, and to establish age-dependent normative data for diotic and dichotic listening conditions in both stationary and interrupted noise.Design:In experiment 1, a newly designed pediatric DIN (pDIN) test was compared with the standard DIN test. Major differences with the DIN test are that the pDIN test uses 79% correct instead of 50% correct as a target point, single digits (except 0) instead of triplets, and animations in the test procedure. In this experiment, 43 normal-hearing subjects between 4 and 12 years of age and 10 adult subjects participated. The authors measured the monaural speech reception threshold for both DIN test and pDIN test using headphones. Experiment 2 used the standard DIN test to measure speech reception thresholds in noise in 112 normal-hearing children between 4 and 12 years of age and 33 adults. The DIN test was applied using headphones in stationary and interrupted noise, and in diotic and dichotic conditions, to study also binaural unmasking and the benefit of listening in the gaps.Results:Most children could reliably do both pDIN test and DIN test, and measurement errors for the pDIN test were comparable between children and adults. There was no significant difference between the score for the pDIN test and that of the DIN test. Speech recognition scores increase with age for all conditions tested, and performance is adult-like by 10 to 12 years of age in stationary noise but not interrupted noise. The youngest, 4-year-old children have speech reception thresholds 3 to 7 dB less favorable than adults, depending on test conditions. The authors found significant age effects on binaural unmasking and fluctuating masker benefit, even after correction for the lower baseline speech reception threshold of adults in stationary noise.Conclusions:Speech recognition in noise abilities develop well into adolescence, and young children need a more favorable signal-to-noise ratio than adults for all listening conditions. Speech recognition abilities in children in stationary and interrupted noise can accurately and reliably be tested using the DIN test. A pediatric version of the test was shown to be unnecessary. Normative data were established for the DIN test in stationary and fluctuating maskers, and in diotic and dichotic conditions. The DIN test can thus be used to test speech recognition abilities for normal-hearing children from the age of 4 years and older.

The Effect of Binaural Beamforming Technology on Speech Intelligibility in Bimodal Cochlear Implant Recipients

Although the benefit of bimodal listening in cochlear implant users has been agreed on, speech comprehension remains a challenge in acoustically complex real-life environments due to reverberation and disturbing background noises. One way to additionally improve bimodal auditory performance is the use of directional microphones. The objective of this study was to investigate the effect of a binaural beamformer for bimodal cochlear implant (CI) users. This prospective study measured speech reception thresholds (SRT) in noise in a repeated-measures design that varied in listening modality for static and dynamic listening conditions. A significant improvement in SRT of 4.7 dB was found with the binaural beamformer switched on in the bimodal static listening condition. No significant improvement was found in the dynamic listening condition. We conclude that there is a clear additional advantage of the binaural beamformer in bimodal CI users for predictable/static listening conditions with frontal target speech and spatially separated noise sources.

Factors Affecting Speech Reception in Background Noise with a Vocoder Implementation of the FAST Algorithm.

Speech segregation in background noise remains a difficult task for individuals with hearing loss. Several signal processing strategies have been developed to improve the efficacy of hearing assistive technologies in complex listening environments. The present study measured speech reception thresholds in normal-hearing listeners attending to a vocoder based on the Fundamental Asynchronous Stimulus Timing algorithm (FAST: Smith et al. 2014), which triggers pulses based on the amplitudes of channel magnitudes in order to preserve envelope timing cues, with two different reconstruction bandwidths (narrowband and broadband) to control the degree of spectrotemporal resolution. Five types of background noise were used including same male talker, female talker, time-reversed male talker, time-reversed female talker, and speech-shaped noise to probe the contributions of different types of speech segregation cues and to elucidate how degradation affects speech reception across these conditions. Maskers were spatialized using head-related transfer functions in order to create co-located and spatially separated conditions. Results indicate that benefits arising from voicing and spatial cues can be preserved using the FAST algorithm but are reduced with a reduction in spectral resolution.

Effectiveness of Directional Microphones in Bilateral/Bimodal Cochlear Implant Users-Impact of Spatial and Temporal Noise Characteristics.

To measure speech reception thresholds (SRTs) in co-located (S0N0) and diffuse noise conditions (multi-source noise field, MSNF) and to assess the impact of beamforming algorithms in MSNF in cochlear implant (CI) users. Non-randomized, open, prospective study. Tertiary referral cochlear implantation center. Participants included 14 CI users (7 bimodal, 7 bilateral) and 14 normal hearing young adults. Cochlear implantation. SRTs were assessed by means of a German matrix sentence test in either continuous or modulated noise. Loudspeakers were configured in two different conditions: S0N0 and MSNF (speech source in front, four speakers distributed at ±28.6 and ±151.4 degrees). In MSNF, the CI speech processor microphone was set in different directional sensitivity settings: standard (sub-cardioid), fixed (super-cardioid), and adaptive. In continuous noise, SRTs of both CI groups were comparable. In modulated noise, bimodal CI users showed lower SRTs than bilateral CI group, but significant benefit from glimpsing was only demonstrated in normal hearing participants. All subject groups showed significant spatial release from masking (i.e., SRT improvement in MSNF compared with S0N0 condition) in continuous noise. A tendency of improved SRT (1 dB bimodal, 2 dB bilateral) with fixed and adaptive directional sensitivity was found which could not be statistically confirmed due to large between-subject variations. The absence of the glimpsing effect in CI users was reaffirmed in the present study. Although very effective in single noise source conditions, the beneficial impact of beamforming algorithms in multiple noise source conditions is poor.

Development and evaluation of the British English coordinate response measure speech-in-noise test as an occupational hearing assessment tool

Objective: The studies described in this article outline the design and development of a British English version of the coordinate response measure (CRM) speech-in-noise (SiN) test. Our interest in the CRM is as a SiN test with high face validity for occupational auditory fitness for duty (AFFD) assessment. Design: Study 1 used the method of constant stimuli to measure and adjust the psychometric functions of each target word, producing a speech corpus with equal intelligibility. After ensuring all the target words had similar intelligibility, for Studies 2 and 3, the CRM was presented in an adaptive procedure in stationary speech-spectrum noise to measure speech reception thresholds and evaluate the test–retest reliability of the CRM SiN test. Study sample: Studies 1 (n = 20) and 2 (n = 30) were completed by normal-hearing civilians. Study 3 (n = 22) was completed by hearing impaired military personnel. Results: The results display good test–retest reliability (95% confidence interval (CI) < 2.1 dB) and concurrent validity when compared to the triple-digit test (r ≤ 0.65), and the CRM is sensitive to hearing impairment. Conclusion: The British English CRM using stationary speech-spectrum noise is a “ready to use” SiN test, suitable for investigation as an AFFD assessment tool for military personnel.

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.

Evaluation of a wireless remote microphone in bimodal cochlear implant recipients

Objective: To evaluate the benefit of a wireless remote microphone (MM) for speech recognition in noise in bimodal adult cochlear implant (CI) users both in a test setting and in daily life. Design: This prospective study measured speech reception thresholds in noise in a repeated measures design with factors including bimodal hearing and MM use. The participants also had a 3-week trial period at home with the MM. Study sample: Thirteen post-lingually deafened adult bimodal CI users. Results: A significant improvement in SRT of 5.4 dB was found between the use of the CI with the MM and the use of the CI without the MM. By also pairing the MM to the hearing aid (HA) another improvement in SRT of 2.2 dB was found compared to the situation with the MM paired to the CI alone. In daily life, participants reported better speech perception for various challenging listening situations, when using the MM in the bimodal condition. Conclusion: There is a clear advantage of bimodal listening (CI and HA) compared to CI alone when applying advanced wireless remote microphone techniques to improve speech understanding in adult bimodal CI users.

The intelligibility of speech in a harmonic masker varying in fundamental frequency contour, broadband temporal envelope, and spatial location

Differences in fundamental frequency (F0), modulations in the masker envelope, and differences in spatial location between a speech target and a masker can improve speech intelligibility in cocktail-party situations. These cues have been thoroughly investigated independently and associated with unmasking mechanisms: F0 segregation, temporal dip listening and spatial unmasking, respectively. Two experiments were conducted to examine whether F0 segregation interacts with spatial unmasking (experiment 1) or temporal modulations in the masker envelope (experiment 2) by measuring speech reception thresholds for a monotonized or an intonated voice against eight types of harmonic complex masker. In experiment 1, the masker varied in F0 contour (monotonized or intonated), mean F0 (0 or 3 semitones above that of the target) and spatial location (co-located or separated from the target). In experiment 2, the masker varied in F0 contour, mean F0 and broadband temporal envelope (stationary or 1-voice modulated). The benefits associated with spatial separation and F0 differences added up linearly in almost all conditions, whereas modulations in the masker envelope improved speech intelligibility only in the presence of intonated maskers. In addition, in both experiments F0 segregation benefited considerably from natural variations in the F0 pattern of the target voice, but was largely disrupted by those of the masker.

Characterizing Speech Intelligibility in Noise After Wide Dynamic Range Compression.

The effects of nonlinear signal processing on speech intelligibility in noise are difficult to evaluate. Often, the effects are examined by comparing speech intelligibility scores with and without processing measured at fixed signal to noise ratios (SNRs) or by comparing the adaptive measured speech reception thresholds corresponding to 50% intelligibility (SRT50) with and without processing. These outcome measures might not be optimal. Measuring at fixed SNRs can be affected by ceiling or floor effects, because the range of relevant SNRs is not know in advance. The SRT50 is less time consuming, has a fixed performance level (i.e., 50% correct), but the SRT50 could give a limited view, because we hypothesize that the effect of most nonlinear signal processing algorithms at the SRT50 cannot be generalized to other points of the psychometric function. In this article, we tested the value of estimating the entire psychometric function. We studied the effect of wide dynamic range compression (WDRC) on speech intelligibility in stationary, and interrupted speech-shaped noise in normal-hearing subjects, using a fast method-based local linear fitting approach and by two adaptive procedures. The measured performance differences for conditions with and without WDRC for the psychometric functions in stationary noise and interrupted speech-shaped noise show that the effects of WDRC on speech intelligibility are SNR dependent. We conclude that favorable and unfavorable effects of WDRC on speech intelligibility can be missed if the results are presented in terms of SRT50 values only.

The effect of fluctuating maskers on speech understanding of high-performing cochlear implant users

Objective: The present study evaluated whether the poorer baseline performance of cochlear implant (CI) users or the technical and/or physiological properties of CI stimulation are responsible for the absence of masking release. Design: This study measured speech reception thresholds (SRTs) in continuous and modulated noise as a function of signal to noise ratio (SNR). Study sample: A total of 24 subjects participated: 12 normal-hearing (NH) listeners and 12 subjects provided with recent MED-EL CI systems. Results: The mean SRT of CI users in continuous noise was −3.0 ± 1.5 dB SNR (mean ± SEM), while the normal-hearing group reached −5.9 ± 0.8 dB SNR. In modulated noise, the difference across groups increased considerably. For CI users, the mean SRT worsened to −1.4 ± 2.3 dB SNR, while it improved for normal-hearing listeners to −18.9 ± 3.8 dB SNR. Conclusions: The detrimental effect of fluctuating maskers on SRTs in CI users shown by prior studies was confirmed by the current study. Concluding, the absence of masking release is mainly caused by the technical and/or physiological properties of CI stimulation, not just the poorer baseline performance of many CI users compared to normal-hearing subjects. Speech understanding in modulated noise was more robust in CI users who had a relatively large electrical dynamic range.

Speech Intelligibility for Target and Masker with Different Spectra.

The speech intelligibility index (SII) calculation is based on the assumption that the effective range of signal-to-noise ratio (SNR) regarding speech intelligibility is [- 15 dB; +15 dB]. In a specific frequency band, speech intelligibility would remain constant by varying the SNRs above + 15 dB or below - 15 dB. These assumptions were tested in four experiments measuring speech reception thresholds (SRTs) with a speech target and speech-spectrum noise, while attenuating target or noise above or below 1400 Hz, with different levels of attenuation in order to test different SNRs in the two bands. SRT varied linearly with attenuation at low-attenuation levels and an asymptote was reached for high-attenuation levels. However, this asymptote was reached (intelligibility was not influenced by further attenuation) for different attenuation levels across experiments. The - 15-dB SII limit was confirmed for high-pass filtered targets, whereas for low-pass filtered targets, intelligibility was further impaired by decreasing the SNR below - 15 dB (until - 37 dB) in the high-frequency band. For high-pass and low-pass filtered noises, speech intelligibility kept improving when increasing the SNR in the rejected band beyond + 15 dB (up to 43 dB). Before reaching the asymptote, a 10-dB increase of SNR obtained by filtering the noise resulted in a larger decrease of SRT than a corresponding 10-dB decrease of SNR obtained by filtering the target (the slopes SRT/attenuation were different depending on which source was filtered). These results question the use of the SNR range and the importance function adopted by the SII when considering sharply filtered signals.