Steady-state Speech-shaped Noise Research Articles

Benefits from Spatial Separation and Fluctuating Masker on Sentence-in-Noise Recognition in Normal-Hearing and Hearing-Impaired Listeners

Purpose: This study examined the spatial separation benefit (SSB) and fluctuating masker benefit (FMB) for sentence-in-noise recognition in normal-hearing (NH) and hearing-impaired (HI) listeners.Methods: Twenty NH listeners and 10 HI listeners who were regular hearing-aid wearers participated in this study. To measure the SSB and the FMB, the Korean Matrix sentence-in-noise scores were obtained using different types of noise (steady-state speech-shaped noise, three sinusoidally amplitude-modulated noises) when the noise was colocated with the target source or was spatially separated by 30° or 60°.Results: For the NH group, the spatial separation between the target and masker was beneficial, regardless of the type of noise. Among the four types of noise, NH listeners performed poorer with speech-shaped noise than with other modulated noises, yielding a substantial improvement in speech-in-noise resulting from the masker’s fluctuation. The amount of SSB or FMB depended on the signal-to-noise ratios for the NH listeners. For HI listeners, the spatial separation was also advantageous in general, and their SSB was slightly greater in unfavorable listening conditions. However, the HI listeners hardly took advantage of the regular temporal dips of the modulated noise, even with the use of their hearing aids.Conclusion: NH listeners benefited from the fluctuation of the masker as well as the spatial separation between sound sources. A positive spatial separation benefit for HI listeners was only observed in an adverse listening condition. Regardless of the modulation rate, HI listeners received little benefit from glimpses of the target speech in the dips of the fluctuating masker. This result can be considered when planning audiological evaluation and rehabilitation for HI listeners.

The Relationship between Speech Perception in Quiet and in Noise for Young Adults with Pure-Tone Thresholds ≤ 25 dB HL.

The standard audiological protocol utilizes quiet measures. However, it has been noted that speech recognition in noise (SRN) testing provides information that cannot be inferred from quiet measures. The purpose of this convergent validity study was to investigate the relationships between behavioral responses in quiet and in noise. Bilateral pure-tone averages (BPTA) were calculated for thresholds from 500 to 6000 Hz. The Hearing in Noise Test (HINT) thresholds in quiet (HINT-Q) were also measured. SRN performances were determined using the HINT Noise Front (HINT-F) condition and the AzBio test. The HINT-F uses steady-state speech-shaped noise and the AzBio uses a 10-talker babble. All conditions were randomized. Fifty young, native English-speaking females with pure-tone thresholds less than or equal to 25 dB HL participated in this study. The average age of the participants was 20.5 years (standard deviation = 1.47). Pearson correlation coefficients were used to quantify the relationships between all measures. Statistically significant relationships were found between HINT-Q thresholds versus BPTA (0.5-6.0 kHz) (r = 0.62, p < 0.01) and between HINT-F thresholds versus AzBio (0 dB signal-to-noise ratio) scores (r = -0.41, p < 0.05). No significant relationships were found between any of the quiet versus noise measures. These results suggest that, for individuals with pure-tone thresholds less than or equal to 25 dB HL, SRN ability must be measured directly and not inferred from PTA or speech-in-quiet measures. It is possible, to a modest degree, to predict AzBio performances from the HINT-F thresholds, and vice versa.

Does having control over background noise affect listening effort or speech perception?

We have previously shown that individual personality traits, including noise sensitivity, can influence listeners’ assessment of effort and frustration related to noise that interferes with a listening task. Here, we extend our previous research to employ stimuli from a commonly used speech-in-noise task, the coordinate response measure (CRM). On each trial, participants heard a sentence of the form “Ready, CALLSIGN, go to COLOR NUMBER now” presented in a background of steady-state speech-shaped noise. They responded by selecting from a multiple-choice display (two callsigns, four colors, and four numbers). After completing one block of 64 trials with 32 sentences presented at a -4 dB SNR and 32 at -8 dB SNR, half of the participants were allowed to choose to change the noise level, making it either “louder” or “softer” for the next 64 trials. The other participants were assigned to either a louder or softer SNR without a choice. Importantly, half of the trials in the “louder” and “softer” conditions were presented at the same SNR (−6 dB), permitting comparison of performance independently of chosen or assigned difficulty. Results will be discussed in terms of implications for future research on noise sensitivity and long-term health.

Preliminary Evaluation of Automated Speech Recognition Apps for the Hearing Impaired and Deaf.

ObjectiveAutomated speech recognition (ASR) systems have become increasingly sophisticated, accurate, and deployable on many digital devices, including on a smartphone. This pilot study aims to examine the speech recognition performance of ASR apps using audiological speech tests. In addition, we compare ASR speech recognition performance to normal hearing and hearing impaired listeners and evaluate if standard clinical audiological tests are a meaningful and quick measure of the performance of ASR apps.MethodsFour apps have been tested on a smartphone, respectively AVA, Earfy, Live Transcribe, and Speechy. The Dutch audiological speech tests performed were speech audiometry in quiet (Dutch CNC-test), Digits-in-Noise (DIN)-test with steady-state speech-shaped noise, sentences in quiet and in averaged long-term speech-shaped spectrum noise (Plomp-test). For comparison, the app's ability to transcribe a spoken dialogue (Dutch and English) was tested.ResultsAll apps scored at least 50% phonemes correct on the Dutch CNC-test for a conversational speech intensity level (65 dB SPL) and achieved 90–100% phoneme recognition at higher intensity levels. On the DIN-test, AVA and Live Transcribe had the lowest (best) signal-to-noise ratio +8 dB. The lowest signal-to-noise measured with the Plomp-test was +8 to 9 dB for Earfy (Android) and Live Transcribe (Android). Overall, the word error rate for the dialogue in English (19–34%) was lower (better) than for the Dutch dialogue (25–66%).ConclusionThe performance of the apps was limited on audiological tests that provide little linguistic context or use low signal to noise levels. For Dutch audiological speech tests in quiet, ASR apps performed similarly to a person with a moderate hearing loss. In noise, the ASR apps performed more poorly than most profoundly deaf people using a hearing aid or cochlear implant. Adding new performance metrics including the semantic difference as a function of SNR and reverberation time could help to monitor and further improve ASR performance.

The Importance of Extended High-Frequency Speech Information in the Recognition of Digits, Words, and Sentences in Quiet and Noise.

In pure-tone audiometry, hearing thresholds are typically measured up to 8 kHz. Recent research has shown that extended high-frequency (EHF; frequencies >8 kHz) speech information improves speech recognition. However, it is unclear whether the EHF benefit is present for different types of speech material. This study assesses the added value of EHF information for speech recognition in noise for digit triplets, consonant-vowel-consonant (CVC) words, and sentences; and for speech recognition in quiet for CVC. Twenty-four young adults with normal-hearing thresholds up to 16 kHz performed a listening experiment in quiet and in noise in a within-subject repeated measures design. Stimuli were presented monaurally. Steady state speech-shaped noise at a fixed signal to noise ratio was used for measurements in noise. Listening conditions varied only in terms of available EHF information. Stimuli were presented in three different conditions: (1) both speech and noise broadband, (2) speech broadband and noise low-pass filtered at 8 kHz, and (3) both speech and noise low-pass filtered at 8 kHz. In the speech-in-quiet experiment, stimuli (CVC) were high-pass filtered at 3 kHz and presented in two conditions: (1) with EHF information and (2) without EHF information. In the speech-in-noise experiment, for all speech material, the highest scores were achieved in the condition where the noise was low-pass filtered at 8 kHz and speech unfiltered; the lowest scores were obtained in the condition where both speech and noise were low-pass filtered at 8 kHz. Adding speech frequencies above 8 kHz improved the median recognition scores by 75.0%, 21.8%, and 23.8% for digit triplets, words, and sentences, respectively, at a fixed signal to noise ratio. In the speech-in-quiet experiment, median recognition scores were 7.8% higher in the condition where the EHF information was available, as opposed to when it was not. Speech information for frequencies above 8 kHz contributes to speech recognition in noise. It also contributes to speech recognition in quiet when information below 3 kHz is absent. Our results suggest that EHFs may be relevant in challenging listening conditions and should be measured in pure-tone audiometry to get a complete picture of a person's hearing. Further, results of speech recognition tests may vary when different recording and/or measurement equipment is used with different frequency responses above 8 kHz.

Diagnostic Accuracy of the AzBio Speech Recognition in Noise Test.

Purpose The goal of this study was to determine the ability of the AzBio speech recognition in noise (SRN) test to distinguish between groups of participants with and without a self-reported SRN disorder and a self-reported signal-to-noise ratio (SNR) loss. Method Fifty-four native English-speaking young adults with normal pure-tone thresholds (≤ 25 dB HL, 0.25-6.0 kHz) participated. Individuals who reported hearing difficulty in a noisy restaurant (Reference Standard 1) were placed in the SRN disorder group. SNR loss groups were created based on the self-report of the ability to hear Hearing in Noise Test (HINT) sentences in steady-state speech-shaped noise, four-talker babble, and 20-talker babble in a controlled listening environment (Reference Standard 2). Participants with HINT thresholds poorer than or equal to the median were assigned to the SNR loss group. Results The area under the curve from the receiver operating characteristics curves revealed that the AzBio test was not a significant predictor of an SRN disorder, or an SNR loss using the steady-state noise Reference Standard 2 condition. However, the AzBio was a significant predictor of an SNR loss using the four-talker babble and 20-talker babble Reference Standard 2 conditions (p < .05). The AzBio was a significant predictor of an SNR loss when using the average HINT thresholds across the three Reference Standard 2 masker conditions (area under the curve = .79, p = .001). Conclusions The AzBio test was not a significant predictor of a self-reported SRN disorder or a self-reported SNR loss in steady-state noise. However, it was a significant predictor of a self-reported SNR loss in babble noise and the average across all noise conditions. A battery of reference standard tests with a range of maskers in a controlled listening environment is recommended for diagnostic accuracy evaluations of SRN tests.

Exploring the effects of phonetic overlap and background noise on incremental processing in children

In everyday conversation, individuals actively process speech in order to comprehend and respond in real-time. As a word unfolds, listeners activate possible lexical candidates and actively determine the target word as soon as possible. This process requires knowledge of one's native spoken language and the ability to recognize individual phonemes. Phonetic overlap between the target and candidate words can influence the speed of lexical access. For example, phonological onset (e.g., candy), but not rhyming words (e.g., sandal), can yield lexical competition with target words (e.g., candle). When the auditory input is spectrally degraded, however, the effect is different: rhyme words have greater lexical competition with target words. The purpose of the present study is to test the extent to which rhyme words compete with target words in the present of background noise. In a visual world paradigm, the present study examines the time course of spoken word recognition when target words (e.g., candle) are contrasted with full (e.g., sandal) and offset (e.g., poodle) rhymes in 5-to-7-year-olds. Target words are presented in both quiet and in steady-state speech-shaped noise at 0 dB SNR. Preliminary data suggest that rhyming overlap does not impact processing in quiet but may show differences in noise.

A convergent validity study: Listening in Spatialized Noise-Sentences (LiSN-S) test and the Hearing in Noise Test (HINT)

Objectives The primary purpose of this study was to compare Listening in Spatialized Noise – Sentence (LiSN-S) test and the Hearing in Noise Test (HINT) thresholds in order to determine if the two tests measure the same construct (convergent validity). The secondary purpose was to determine performance differences between the two test protocols. The third purpose was to determine the relationships between quiet measures (pure-tone average [PTA] and HINT Quiet thresholds) vs. speech-in-noise performances. Design Statistical analyses included descriptive statistics, Spearman rho statistic, repeated measures analysis of variance (ANOVA) and linear mixed model analyses. Study sample: Fifty-six young adults with normal PTAs (≤15 dB HL for 0.5–4.0 kHz) participated in this study. Results No statistically significant relationships were found between LiSN-S and HINT measures (poor convergent validity). However, statistically significant relationships were found between the quiet measures (HINT Quiet thresholds and average PTA(0.5–4.0 kHz)) vs. the LiSN-S (same and different voices) ±90° performances. Conclusion LiSN-S performances in two-talker babble cannot be generalized to the ability to recognise HINT sentences in steady-state speech-shaped noise, and vice versa. The results imply that LiSN-S ± 90° thresholds were influenced by hearing sensitivity or by supra-threshold distortions that co-vary with hearing sensitivity.

Auditory, Cognitive, and Linguistic Factors Predict Speech Recognition in Adverse Listening Conditions for Children With Hearing Loss.

Objectives: Children with hearing loss listen and learn in environments with noise and reverberation, but perform more poorly in noise and reverberation than children with normal hearing. Even with amplification, individual differences in speech recognition are observed among children with hearing loss. Few studies have examined the factors that support speech understanding in noise and reverberation for this population. This study applied the theoretical framework of the Ease of Language Understanding (ELU) model to examine the influence of auditory, cognitive, and linguistic factors on speech recognition in noise and reverberation for children with hearing loss.Design: Fifty-six children with hearing loss and 50 age-matched children with normal hearing who were 7–10 years-old participated in this study. Aided sentence recognition was measured using an adaptive procedure to determine the signal-to-noise ratio for 50% correct (SNR50) recognition in steady-state speech-shaped noise. SNR50 was also measured with noise plus a simulation of 600 ms reverberation time. Receptive vocabulary, auditory attention, and visuospatial working memory were measured. Aided speech audibility indexed by the Speech Intelligibility Index was measured through the hearing aids of children with hearing loss.Results: Children with hearing loss had poorer aided speech recognition in noise and reverberation than children with typical hearing. Children with higher receptive vocabulary and working memory skills had better speech recognition in noise and noise plus reverberation than peers with poorer skills in these domains. Children with hearing loss with higher aided audibility had better speech recognition in noise and reverberation than peers with poorer audibility. Better audibility was also associated with stronger language skills.Conclusions: Children with hearing loss are at considerable risk for poor speech understanding in noise and in conditions with noise and reverberation. Consistent with the predictions of the ELU model, children with stronger vocabulary and working memory abilities performed better than peers with poorer skills in these domains. Better aided speech audibility was associated with better recognition in noise and noise plus reverberation conditions for children with hearing loss. Speech audibility had direct effects on speech recognition in noise and reverberation and cumulative effects on speech recognition in noise through a positive association with language development over time.

Listening while balancing: Dual-task costs in speech vs. noise maskers

Many middle-aged adults report that listening is effortful in adverse communication situations. One means of quantifying listening effort is by measuring dual-task costs. The present study examined the influence of early aging on dual-task costs using a technique which required participants (younger and middle-aged adults) to complete a postural control task while listening to speech. For the postural control task, participants stood on a force platform and had to maintain their center of pressure within a prescribed area (denoted using real-time visual feedback). Two speech perception tasks were used, each presented with two types of maskers (same-sex two-talker speech masker and steady-state speech-shaped noise): repeating back low-predictability sentences, and listening to Connected Speech Test passages and then answering content questions based on each passage. This presentation will describe data analyses designed to uncover how listener age group and masker type influenced listening effort as measured by dual-task costs. [Work supported by NIDCD 012057.]

The Relationship between Random Gap Detection and Hearing in Noise Test Performances.

Temporal acoustic cues are particularly important for speech understanding, and past research has inferred a relationship between temporal resolution and speech recognition in noise ability. A temporal resolution disorder is thought to affect speech understanding abilities because persons would not be able to accurately encode these frequency transitions, creating speech discrimination errors even in the presence of normal pure-tone hearing. The primary purpose was to investigate the relationship between temporal resolution as measured by the Random Gap Detection Test (RGDT) and speech recognition in noise performance as measured by the Hearing in Noise Test (HINT) in adults with normal audiometric thresholds. The second purpose was to examine the relationship between temporal resolution and spatial release from masking. The HINT and RGDT protocols were administered under headphones according to the guidelines specified by the developers. The HINT uses an adaptive protocol to determine the signal-to-noise ratio where the participant recognizes 50% of the sentences. For HINT conditions, the target sentences were presented at 0° and the steady-state speech-shaped noise and a four-talker babble (4TB) was presented at 0°, +90°, or -90° for noise front, noise right, and noise left conditions, respectively. The RGDT is used to evaluate temporal resolution by determining the smallest time interval between two matching stimuli that can be detected by the participant. The RGDT threshold is the shortest time interval where the participant detects a gap. Tonal (0.5, 1, 2, and 4 kHz) and click stimuli random gap subtests were presented at 60 dB HL. Tonal subtests were presented in a random order to minimize presentation order effects. Twenty-one young, native English-speaking participants with normal pure-tone thresholds (≤25 dB HL for 500-4000 Hz) participated in this study. The average age of the participants was 20.2 years (SD = 0.66). Spearman rho correlation coefficients were conducted using SPSS 22 (IBM Corp., Armonk, NY) to determine the relationships between HINT and RGDT thresholds and derived measures (spatial advantage and composite scores). Nonparametric testing was used because of the ordinal nature of RGDT data. Moderate negative correlations (p < 0.05) were found between eight RGDT and HINT threshold measures and a moderate positive correlation (p < 0.05) was found between RGDT click thresholds and HINT 4TB spatial advantage. This suggests that as temporal resolution abilities worsened, speech recognition in noise performance improved. These correlations were not statistically significant after the p value reflected the Bonferroni correction for multiple comparisons. The results of the present study imply that the RGDT and HINT use different temporal processes. Performance on the RGDT cannot be predicted from HINT thresholds or vice versa.

Gender, the individual, and intelligibility

In the clinic and in the laboratory, opinions differ on the relative intelligibility of the speech of women and men. However, the effect of gender alone has rarely been studied explicitly. Here we present a study of 30 talkers (15 male) and 32 listeners assessing intelligibility of a 180-sentence subset of the IEEE sentences presented in steady-state speech-shaped noise. Four signal-to-noise ratios (−4, −2, 0, + 2 dB SNR) were tested with 45 sentences each. Results showed substantial overlap between intelligibility scores for each gender. Although standard statistical approaches show a slight advantage for female talkers at all SNRs, post-hoc analyses indicated that the gender effect is an artifact driven by a few particularly unintelligible males. These results do not address intrinsic gender-related differences in speech intensity, or in the ability to overcome background noise by speaking clearly, but suggest that gender-related differences are negligible when those factors are controlled. More generally, even with a large sample of talkers, the high degree of talker-intrinsic variability in intelligibility can lead to conclusions that do not generalize to the population of interest, an issue that could affect comparisons rooted in gender, dialect, or other social factors.

Relationship between speech-evoked neural responses and perception of speech in noise in older adults.

Speech-in-noise (SPIN) perception involves neural encoding of temporal acoustic cues. Cues include temporal fine structure (TFS) and envelopes that modulate at syllable (Slow-rate ENV) and fundamental frequency (F0-rate ENV) rates. Here the relationship between speech-evoked neural responses to these cues and SPIN perception was investigated in older adults. Theta-band phase-locking values (PLVs) that reflect cortical sensitivity to Slow-rate ENV and peripheral/brainstem frequency-following responses phase-locked to F0-rate ENV (FFRENV_F0) and TFS (FFRTFS) were measured from scalp-electroencephalography responses to a repeated speech syllable in steady-state speech-shaped noise (SpN) and 16-speaker babble noise (BbN). The results showed that (1) SPIN performance and PLVs were significantly higher under SpN than BbN, implying differential cortical encoding may serve as the neural mechanism of SPIN performance that varies as a function of noise types; (2) PLVs and FFRTFS at resolved harmonics were significantly related to good SPIN performance, supporting the importance of phase-locked neural encoding of Slow-rate ENV and TFS of resolved harmonics during SPIN perception; (3) FFRENV_F0 was not associated to SPIN performance until audiometric threshold was controlled for, indicating that hearing loss should be carefully controlled when studying the role of neural encoding of F0-rate ENV. Implications are drawn with respect to fitting auditory prostheses.

Assessing the effect of noise-reduction to the intelligibility of low-pass filtered speech.

Given the fact that most hearing-impaired listeners have low-frequency residual hearing, the present work assessed the effect of applying commonly-used singlechannel noise-reduction (NR) algorithms to improve the intelligibility of low-pass filtered speech, which simulates the effect of understanding speech with low-frequency residual hearing of hearing-impaired patients. In addition, this study was performed with Mandarin speech, which is characterized by its significant contribution of information present in (low-frequency dominated) vowels to speech intelligibility. Mandarin sentences were corrupted by steady-state speech-shaped noise and processed by four types (i.e., subspace, statistical-modeling, spectral-subtractive, and Wiener-filtering) of single-channel NR algorithms. The processed sentences were played to normal-hearing listeners for recognition. Experimental results showed that existing single-channel NR algorithms were unable to improve the intelligibility of low-pass filtered Mandarin sentences. Wiener-filtering had the least negative influence to the intelligibility of low-pass filtered speech among the four types of single-channel NR algorithms examined.

Memory performance on the Auditory Inference Span Test is independent of background noise type for young adults with normal hearing at high speech intelligibility.

Listening in noise is often perceived to be effortful. This is partly because cognitive resources are engaged in separating the target signal from background noise, leaving fewer resources for storage and processing of the content of the message in working memory. The Auditory Inference Span Test (AIST) is designed to assess listening effort by measuring the ability to maintain and process heard information. The aim of this study was to use AIST to investigate the effect of background noise types and signal-to-noise ratio (SNR) on listening effort, as a function of working memory capacity (WMC) and updating ability (UA). The AIST was administered in three types of background noise: steady-state speech-shaped noise, amplitude modulated speech-shaped noise, and unintelligible speech. Three SNRs targeting 90% speech intelligibility or better were used in each of the three noise types, giving nine different conditions. The reading span test assessed WMC, while UA was assessed with the letter memory test. Twenty young adults with normal hearing participated in the study. Results showed that AIST performance was not influenced by noise type at the same intelligibility level, but became worse with worse SNR when background noise was speech-like. Performance on AIST also decreased with increasing memory load level. Correlations between AIST performance and the cognitive measurements suggested that WMC is of more importance for listening when SNRs are worse, while UA is of more importance for listening in easier SNRs. The results indicated that in young adults with normal hearing, the effort involved in listening in noise at high intelligibility levels is independent of the noise type. However, when noise is speech-like and intelligibility decreases, listening effort increases, probably due to extra demands on cognitive resources added by the informational masking created by the speech fragments and vocal sounds in the background noise.

The role of auditory and cognitive factors in understanding speech in noise by normal-hearing older listeners.

Normal-hearing older adults often experience increased difficulties understanding speech in noise. In addition, they benefit less from amplitude fluctuations in the masker. These difficulties may be attributed to an age-related auditory temporal processing deficit. However, a decline in cognitive processing likely also plays an important role. This study examined the relative contribution of declines in both auditory and cognitive processing to the speech in noise performance in older adults. Participants included older (60–72 years) and younger (19–29 years) adults with normal hearing. Speech reception thresholds (SRTs) were measured for sentences in steady-state speech-shaped noise (SS), 10-Hz sinusoidally amplitude-modulated speech-shaped noise (AM), and two-talker babble. In addition, auditory temporal processing abilities were assessed by measuring thresholds for gap, amplitude-modulation, and frequency-modulation detection. Measures of processing speed, attention, working memory, Text Reception Threshold (a visual analog of the SRT), and reading ability were also obtained. Of primary interest was the extent to which the various measures correlate with listeners' abilities to perceive speech in noise. SRTs were significantly worse for older adults in the presence of two-talker babble but not SS and AM noise. In addition, older adults showed some cognitive processing declines (working memory and processing speed) although no declines in auditory temporal processing. However, working memory and processing speed did not correlate significantly with SRTs in babble. Despite declines in cognitive processing, normal-hearing older adults do not necessarily have problems understanding speech in noise as SRTs in SS and AM noise did not differ significantly between the two groups. Moreover, while older adults had higher SRTs in two-talker babble, this could not be explained by age-related cognitive declines in working memory or processing speed.

The Contribution of Matched Envelope Dynamic Range to the Binaural Benefits in Simulated Bilateral Electric Hearing

This study examined the effects of envelope dynamic-range mismatch on the intelligibility of Mandarin speech in noise by simulated bilateral electric hearing. Noise-vocoded Mandarin speech, corrupted by speech-shaped noise at 5 and 0 dB signal-to-noise ratios, was presented unilaterally or bilaterally to 10 normal-hearing listeners for recognition. For unilateral conditions, the right ear was presented with the 8-channel noise-vocoded stimuli generated using a 15-dB envelope dynamic range (DR). To simulate the envelope DR mismatch between the 2 ears, the left ear was presented with the 8-channel noise-vocoded stimuli generated using a 5-, 10-, or 15-dB envelope DR, respectively. Significant binaural summation benefits for Mandarin speech recognition were observed only with matched envelope DR between the 2 ears. With reduced DR, the performance of tone identification was more consistent in the steady-state speech-shaped noise than that of sentence recognition. Consistent with previous findings, the present results suggest that Mandarin speech-perception performance of bilateral electric listening in noise is affected by the difference of envelope DR between the 2 implanted ears, and the binaural summation benefits are maximized when DR mismatch is minimized between the 2 implanted ears.

Companding to improve cochlear-implant speech recognition in speech-shaped noise

Nonlinear sensory and neural processing mechanisms have been exploited to enhance spectral contrast for improvement of speech understanding in noise. The "companding" algorithm employs both two-tone suppression and adaptive gain mechanisms to achieve spectral enhancement. This study implemented a 50-channel companding strategy and evaluated its efficiency as a front-end noise suppression technique in cochlear implants. The key parameters were identified and evaluated to optimize the companding performance. Both normal-hearing (NH) listeners and cochlear-implant (CI) users performed phoneme and sentence recognition tests in quiet and in steady-state speech-shaped noise. Data from the NH listeners showed that for noise conditions, the implemented strategy improved vowel perception but not consonant and sentence perception. However, the CI users showed significant improvements in both phoneme and sentence perception in noise. Maximum average improvement for vowel recognition was 21.3 percentage points (p<0.05) at 0 dB signal-to-noise ratio (SNR), followed by 17.7 percentage points (p<0.05) at 5 dB SNR for sentence recognition and 12.1 percentage points (p<0.05) at 5 dB SNR for consonant recognition. While the observed results could be attributed to the enhanced spectral contrast, it is likely that the corresponding temporal changes caused by companding also played a significant role and should be addressed by future studies.

Effects of introducing unprocessed low-frequency information on the reception of envelope-vocoder processed speech

This study investigated the benefits of adding unprocessed low-frequency information to acoustic simulations of cochlear-implant processing in normal-hearing listeners. Implant processing was simulated using an eight-channel noise-excited envelope vocoder, and low-frequency information was added by replacing the lower frequency channels of the processor with a low-pass-filtered version of the original stimulus. Experiment 1 measured sentence-level speech reception as a function of target-to-masker ratio, with either steady-state speech-shaped noise or single-talker maskers. Experiment 2 measured listeners' ability to identify two vowels presented simultaneously, as a function of the F0 difference between the two vowels. In both experiments low-frequency information was added below either 300 or 600 Hz. The introduction of the additional low-frequency information led to substantial and significant improvements in performance in both experiments, with a greater improvement observed for the higher (600 Hz) than for the lower (300 Hz) cutoff frequency. However, performance never equaled performance in the unprocessed conditions. The results confirm other recent demonstrations that added low-frequency information can provide significant benefits in intelligibility, which may at least in part be attributed to improvements in F0 representation. The findings provide further support for efforts to make use of residual acoustic hearing in cochlear-implant users.