Variations in the slope of the psychometric functions for speech intelligibility: a systematic survey

The value of headphone accommodations in Apple Airpods Pro for managing speech-in-noise hearing difficulties of individuals with normal audiograms

OBJECTIVE

To investigate the extent to which Headphone Accommodations in Apple AirPods Pro attend to the hearing needs of individuals with normal audiograms who experience hearing difficulties in noisy environments.

DESIGN

Single-arm interventional study using acoustic measures, speech-in-noise laboratory testing, and real-world measures via questionnaires and ecological momentary assessment.

STUDY SAMPLE

Seventeen normal-hearing individuals (9 female, 21-59 years) with self-reported hearing-in-noise difficulties.

RESULTS

Acoustic measures showed that, relative to unaided, AirPods Pro provided a SNR advantage of +5.4 dB. Speech intelligibility performance in laboratory testing increased 11.8% with AirPods Pro, relative to unaided. On average, participants trialling AirPods Pro in real-world noisy venues reported that their overall hearing experience was a bit better than without them. Five participants (29%) reported that they would continue using AirPods Pro in the future. The most relevant barriers that would discourage their future use were limited hearing benefit, discomfort, and stigma.

CONCLUSIONS

Occasional use of AirPods Pro may help some individuals with normal audiograms ameliorate their speech-in-noise hearing difficulties. The identified barriers may inspire the development of new technological solutions aimed at providing an optimal management strategy for the hearing difficulties of this segment of the population.

Speech Perception in Noise and Medial Olivocochlear Reflex: Effects of Age, Speech Stimulus, and Response-Related Variables

PURPOSE

The role of the medial olivocochlear system in speech perception in noise has been debated over the years, with studies showing mixed results. One possible reason for this could be the dependence of this relationship on the parameters used in assessing the speech perception ability (age, stimulus, and response-related variables).

METHODS

The current study assessed the influence of the type of speech stimuli (monosyllables, words, and sentences), the signal-to-noise ratio (+5, 0, -5, and -10 dB), the metric used to quantify the speech perception ability (percent-correct, SNR-50, and slope of the psychometric function) and age (young vs old) on the relationship between medial olivocochlear reflex (quantified by contralateral inhibition of transient evoked otoacoustic emissions) and speech perception in noise.

RESULTS

A linear mixed-effects model revealed no significant contributions of the medial olivocochlear reflex to speech perception in noise.

CONCLUSION

The results suggest that there was no evidence of any modulatory influence of the indirectly measured medial olivocochlear reflex strength on speech perception in noise.

Individual differences in speech-on-speech masking are correlated with cognitive and visual task performance

Individual differences in spatial tuning for masked target speech identification were determined using maskers that varied in type and proximity to the target source. The maskers were chosen to produce three strengths of informational masking (IM): high [same-gender, speech-on-speech (SOS) masking], intermediate (the same masker speech time-reversed), and low (speech-shaped, speech-envelope-modulated noise). Typical for this task, individual differences increased as IM increased, while overall performance decreased. To determine the extent to which auditory performance might generalize to another sensory modality, a comparison visual task was also implemented. Visual search time was measured for identifying a cued object among "clouds" of distractors that were varied symmetrically in proximity to the target. The visual maskers also were chosen to produce three strengths of an analog of IM based on feature similarities between the target and maskers. Significant correlations were found for overall auditory and visual task performance, and both of these measures were correlated with an index of general cognitive reasoning. Overall, the findings provide qualified support for the proposition that the ability of an individual to solve IM-dominated tasks depends on cognitive mechanisms that operate in common across sensory modalities.

Cultural differences in auditory ecology

Demographic differences in acoustic environments are usually studied using geographic area monitoring. This approach, however, may miss valuable information differentiating cultures. This motivated the current study, which used wearable sound recorders to measure noise levels and speech-to-noise ratios (SNRs) in the immediate acoustic environment of Latinx and European-American college students. Latinx experienced higher noise levels (64.8 dBC) and lower SNRs (3.7 dB) compared to European-Americans (noise levels, 63 dB; SNRs, 5.4 dB). This work provides a framework for a larger study on the impact of culture on auditory ecology.

Optimised adaptive procedures and analysis methods for conducting speech-in-noise tests

OBJECTIVE

Speech-in-noise testing is a valuable part of audiological test batteries. Test standardisation using precise methods is desirable for ease of administration. This study investigated the accuracy and reliability of different Bayesian and non-Bayesian adaptive procedures and analysis methods for conducting speech-in-noise testing.

DESIGN

Matrix sentence tests using different numbers of sentences (10, 20, 30 and 50) and target intelligibilities (50 and 75%) were simulated for modelled listeners with various characteristics. The accuracy and reliability of seven different measurement procedures and three different data analysis methods were assessed.

RESULTS

The estimation of 50% intelligibility was accurate and showed excellent reliability across the majority of methods tested, even with relatively few stimuli. Estimating 75% intelligibility resulted in decreased accuracy. For this target, more stimuli were required for sufficient accuracy and selected Bayesian procedures surpassed the performance of others. Some Bayesian procedures were also superior in the estimation of psychometric function width.

CONCLUSIONS

A single standardised procedure could improve the consistency of the matrix sentence test across a range of target intelligibilities. Candidate adaptive procedures and analysis methods are discussed. These could also be applicable for other speech materials. Further testing with human participants is required.

Spectral weighting for sentence recognition in steady-state and amplitude-modulated noise

Spectral weights in octave-frequency bands from 0.25 to 4 kHz were estimated for speech-in-noise recognition using two sentence materials (i.e., the IEEE and AzBio sentences). The masking noise was either unmodulated or sinusoidally amplitude-modulated at 8 Hz. The estimated spectral weights did not vary significantly across two test sessions and were similar for the two sentence materials. Amplitude-modulating the masker increased the weight at 2 kHz and decreased the weight at 0.25 kHz, which may support an upward shift in spectral weights for temporally fluctuating maskers.

Modeling the effect of linguistic predictability on speech intelligibility prediction

Many existing speech intelligibility prediction (SIP) algorithms can only account for acoustic factors affecting speech intelligibility and cannot predict intelligibility across corpora with different linguistic predictability. To address this, a linguistic component was added to five existing SIP algorithms by estimating linguistic corpus predictability using a pre-trained language model. The results showed improved SIP performance in terms of correlation and prediction error over a mixture of four datasets, each with a different English open-set corpus.

Verification of Estimated Output Signal-to-Noise Ratios From a Phase Inversion Technique Using a Simulated Hearing Aid

PURPOSE

The signal-to-noise ratio (SNR) for speech presented in background noise may vary after being processed by digital hearing aids with nonlinear signal processing algorithms, such as wide dynamic range compression (WDRC). A phase inversion technique has been previously developed to assess the output SNR of hearing aids. However, systematic validations of this technique have not been conducted. This study aims to validate the phase inversion technique.

METHOD

A simulated hearing aid with multichannel WDRC was implemented, from which the output SNRs, computed via shadow filtering, for connected speech in background noise were directly computed. The agreement between the shadow filter output SNRs and those estimated using the phase inversion technique for the same stimuli was utilized to validate the phase inversion technique. The background noise was 2- or 20-talker babble noise, and the speech stimuli were presented at SNRs of -10 to +10 dB at the input of the simulated hearing aid. The simulated hearing aid was configured to provide amplification for four representative audiograms, and the WDRC was set to be fast or slow acting. To investigate the effects of additive noise, independent of the presented noise stimulus, on the phase inversion estimated output SNR, the same simulated hearing aid was implemented with an additive Gaussian noise at its input (45 and 60 dB SPL).

RESULTS

Results showed that the phase inversion technique could either overestimate or underestimate output SNR, depending on the test condition; the estimation errors tended to coincide with temporal landmarks, such as natural pauses between consecutive sentences or fricatives; and increasing the simulated noise led to poorer estimates of output SNR.

CONCLUSIONS

Results imply that the accuracy of the phase inversion technique is dependent on the test conditions. Thus, the phase inversion technique should be used with caution, and its validity should be evaluated further.

BPACE: A Bayesian, Patient-Centered Procedure for Matrix Speech Tests in Noise

Matrix sentence tests in noise can be challenging to the listener and time-consuming. A trade-off should be found between testing time, listener's comfort and the precision of the results. Here, a novel test procedure based on an updated maximum likelihood method was developed and implemented in a German matrix sentence test. It determines the parameters of the psychometric function (threshold, slope, and lapse-rate) without constantly challenging the listener at the intelligibility threshold. A so-called "credible interval" was used as a mid-run estimate of reliability and can be used as a termination criterion for the test. The procedure was evaluated and compared to a STAIRCASE procedure in a study with 20 cochlear implant patients and 20 normal hearing participants. The proposed procedure offers comparable accuracy and reliability to the reference method, but with a lower listening effort, as rated by the listeners (- 1.8 points on a 10-point scale). Test duration can be reduced by 1.3 min on average when a credible interval of 2 dB is used as the termination criterion instead of testing 30 sentences. Particularly, normal hearing listeners and well performing, cochlear implant users can benefit from shorter test duration. Although the novel procedure was developed for a German test, it can easily be applied to tests in any other language.

The Effect of Age, Type of Noise, and Cochlear Implants on Adaptive Sentence-in-Noise Task

Adaptive tests of sentences in noise mimic the challenge of daily listening situations. The aims of the present study were to validate an adaptive version of the HeBio sentence test on normal hearing (NH) adults; to evaluate the effect of age and type of noise on speech reception threshold in noise (SRTn); and to test it on prelingual adults with cochlear implants (CI). In Experiment 1, 45 NH young adults listened to two lists accompanied by four-talker babble noise (4TBN). Experiment 2 presented the sentences amidst 4TBN or speech-shaped noise (SSN) to 80 participants in four age groups. In Experiment 3, 18 CI adult users with prelingual bilateral profound hearing loss performed the test amidst SSN, along with HeBio sentences and monosyllabic words in quiet and forward digits span. The main findings were as follows: SRTn for NH participants was normally distributed and had high test–retest reliability; SRTn was lower among adolescents and young adults than middle-aged and older adults, and were better for SSN than 4TBN; SRTn for CI users was higher and more variant than for NH and correlated with speech perception tests in quiet, digits span, and age at first CI. This suggests that the adaptive HeBio can be implemented in clinical and research settings with various populations.

Intelligibility and detectability of speech measured diotically and dichotically in groups of listeners with, at most, "slight" hearing loss

The purpose of this investigation was to determine if a group of listeners having thresholds at 4 kHz exceeding 7.5 dB HL, and no more than "slight" hearing loss, would exhibit degradations in performance when "target" stimuli were masked tokens of speech. Intelligibility thresholds and detection thresholds were measured separately for speech masked by flat-spectrum noise or speech-shaped noise. Both NoSo and NoSπ configurations were employed. Consistent with findings of earlier investigations, when maskers and speech tokens were broadband, NoSo and NoSπ detection thresholds were substantially lower than intelligibility thresholds. More importantly, for the small cohorts tested, mean thresholds obtained from the ≤7.5 dB and >7.5 dB groups were equivalent. When maskers and speech targets were high-pass filtered at 500 Hz and above, the mean intelligibility thresholds obtained from the >7.5 dB group were about 4 dB higher than those obtained from the ≤7.5 dB group, independent of masker type and interaural configuration of the stimuli. In real-world listening situations, such deficits may manifest themselves as substantially reduced speech intelligibility and, perhaps, increased "listening effort" for listeners whose thresholds at 4 kHz exceed 7.5 dB HL and who have no more than "slight" hearing loss.

Speech Recognition and Listening Effort in Cochlear Implant Recipients and Normal-Hearing Listeners

The outcome of cochlear implantation is typically assessed by speech recognition tests in quiet and in noise. Many cochlear implant recipients reveal satisfactory speech recognition especially in quiet situations. However, since cochlear implants provide only limited spectro-temporal cues the effort associated with understanding speech might be increased. In this respect, measures of listening effort could give important extra information regarding the outcome of cochlear implantation. In order to shed light on this topic and to gain knowledge for clinical applications we compared speech recognition and listening effort in cochlear implants (CI) recipients and age-matched normal-hearing listeners while considering potential influential factors, such as cognitive abilities. Importantly, we estimated speech recognition functions for both listener groups and compared listening effort at similar performance level. Therefore, a subjective listening effort test (adaptive scaling, “ACALES”) as well as an objective test (dual-task paradigm) were applied and compared. Regarding speech recognition CI users needed about 4 dB better signal-to-noise ratio to reach the same performance level of 50% as NH listeners and even 5 dB better SNR to reach 80% speech recognition revealing shallower psychometric functions in the CI listeners. However, when targeting a fixed speech intelligibility of 50 and 80%, respectively, CI users and normal hearing listeners did not differ significantly in terms of listening effort. This applied for both the subjective and the objective estimation. Outcome for subjective and objective listening effort was not correlated with each other nor with age or cognitive abilities of the listeners. This study did not give evidence that CI users and NH listeners differ in terms of listening effort – at least when the same performance level is considered. In contrast, both listener groups showed large inter-individual differences in effort determined with the subjective scaling and the objective dual-task. Potential clinical implications of how to assess listening effort as an outcome measure for hearing rehabilitation are discussed.

A comparison of speech intelligibility and subjective quality with hearing-aid processing in older adults with hearing loss

OBJECTIVE

This study characterised the relationship between speech intelligibility and quality in listeners with hearing loss for a range of hearing-aid processing settings and acoustic conditions.

DESIGN

Binaural speech intelligibility scores and quality ratings were measured for sentences presented in babble noise and processed through a hearing-aid simulation. The intelligibility-quality relationship was investigated by (1) assessing the effects of experimental conditions on each task; (2) directly comparing intelligibility scores and quality ratings for each participant across the range of conditions; and (3) comparing the association between signal envelope fidelity (represented by a cepstral correlation metric) and intelligibility and quality.

STUDY SAMPLE

Participants were 15 adults (7 females; age range 59-81 years) with mild to moderately severe sensorineural hearing loss.

RESULTS

Intelligibility and quality showed a positive association both with each other and with changes to signal fidelity introduced by the entire acoustic and signal-processing system including the additive noise and the hearing-aid output. As signal fidelity decreased, quality ratings changed at a slower rate than intelligibility scores. Individual psychometric functions were more variable for quality compared to intelligibility.

CONCLUSIONS

Variability in the intelligibility-quality relationship reinforces the importance of measuring both intelligibility and quality in clinical hearing-aid fittings.

The Effects of Uncertainty in Level on Speech-on-Speech Masking

Identification of speech from a "target" talker was measured in a speech-on-speech masking task with two simultaneous "masker" talkers. The overall level of each talker was either fixed or randomized throughout each stimulus presentation to investigate the effectiveness of level as a cue for segregating competing talkers and attending to the target. Experimental manipulations included varying the level difference between talkers and imposing three types of target level uncertainty: 1) fixed target level across trials, 2) random target level across trials, or 3) random target levels on a word-by-word basis within a trial. When the target level was predictable performance was better than corresponding conditions when the target level was uncertain. Masker confusions were consistent with a high degree of informational masking (IM). Furthermore, evidence was found for "tuning" in level and a level "release" from IM. These findings suggest that conforming to listener expectation about relative level, in addition to cues signaling talker identity, facilitates segregation of, and maintaining focus of attention on, a specific talker in multiple-talker communication situations.

Development of Masked Speech Detection Thresholds in 2- to 15-year-old Children: Speech-Shaped Noise and Two-Talker Speech Maskers

OBJECTIVES

On the basis of the data from school-aged children, there is consistent evidence that there is a prolonged course of auditory development for perceiving speech embedded in competing background sounds. Furthermore, age-related differences are prolonged and pronounced for a two-talker speech masker compared to a speech-shaped noise masker. However, little is known about the course of development during the toddler and preschool years because it is difficult to collect reliable behavioral data from this age range. The goal of this study was to extend our lower age limit to include toddlers and preschoolers to characterize the developmental trajectory for masked speech detection thresholds across childhood.

DESIGN

Participants were 2- to 15-year-old children (n = 67) and adults (n = 17), all with normal hearing. Thresholds (71%) were measured for detecting a two-syllable word embedded in one of two maskers: speech-shaped noise or two-talker speech. The masker was presented at 55 dB SPL throughout testing. Stimuli were presented to the left ear via a lightweight headphone. Data were collected using an observer-based testing method in which the participant's behavior was judged by an experimenter using a two-interval, two-alternative testing paradigm. The participant's response to the stimulus was shaped by training him/her to perform a conditioned play-based response to the sound. For children, receptive vocabulary and working memory were measured. Data were fitted with a linear regression model to establish the course of development for each masker condition. Appropriateness of the test method was also evaluated by determining if there were age-related differences in training data, inter-rater reliability, or slope or upper asymptote estimates from pooled psychometric functions across different age groups.

RESULTS

Child and adult speech detection thresholds were poorer in the two-talker masker than in the speech-shaped noise masker, but different developmental trajectories were seen for the two masker conditions. For the speech-shaped noise masker, threshold improved by about 5 dB across the age span tested, with adult-like performance being reached around 10 years of age. For the two-talker masker condition, thresholds improved by about 7 dB between 2.5 and 15 years. However, the linear fit for this condition failed to achieve adult-like performance because of limited data from teenagers. No significant age-related differences were seen in training data, probe hit rate, or inter-rater reliability. Furthermore, slope and upper asymptote estimates from pooled psychometric functions were similar across different child age groups.

CONCLUSIONS

Different developmental patterns were seen across the two maskers, with more pronounced child-adult differences and prolonged immaturity during childhood for the two-talker masker relative to the speech-shaped noise masker. Our data do not support the idea that there is rapid improvement of masked speech detection thresholds between 2.5 and 5 years of age. This study also highlights that our observer-based method can be used to collect reliable behavioral data from toddlers and preschoolers-a time period where we know little about auditory development.

An analytical method to convert between speech recognition thresholds and percentage-correct scores for speech-in-noise tests

Speech-in-noise tests use fixed signal-to-noise ratio (SNR) procedures to measure the percentage of correctly recognized speech items at a fixed SNR or use adaptive procedures to measure the SNR corresponding to 50% correct (i.e., the speech recognition threshold, SRT). A direct comparison of these measures is not possible yet. The aim of the present study was to demonstrate that these measures can be converted when the speech-in-noise test meets specific criteria. Formulae to convert between SRT and percentage-correct were derived from basic concepts that underlie standard speech recognition models. Information about the audiogram is not being used in the proposed method. The method was validated by comparing the direct conversion by these formulae with the conversion using the more elaborate Speech Intelligibility Index model and a representative set of 60 audiograms (r = 0.993 and r = 0.994, respectively). Finally, the method was experimentally validated with the Afrikaans sentence-in-noise test (r = 0.866). The proposed formulae can be used when the speech-in-noise test uses steady-state masking noise that matches the spectrum of the speech. Because pure tone thresholds are not required for these calculations, the method is widely applicable.

School-age children benefit from voice gender cue differences for the perception of speech in competing speech

Differences in speakers' voice characteristics, such as mean fundamental frequency (F0) and vocal-tract length (VTL), that primarily define speakers' so-called perceived voice gender facilitate the perception of speech in competing speech. Perceiving speech in competing speech is particularly challenging for children, which may relate to their lower sensitivity to differences in voice characteristics than adults. This study investigated the development of the benefit from F0 and VTL differences in school-age children (4-12 years) for separating two competing speakers while tasked with comprehending one of them and also the relationship between this benefit and their corresponding voice discrimination thresholds. Children benefited from differences in F0, VTL, or both cues at all ages tested. This benefit proportionally remained the same across age, although overall accuracy continued to differ from that of adults. Additionally, children's benefit from F0 and VTL differences and their overall accuracy were not related to their discrimination thresholds. Hence, although children's voice discrimination thresholds and speech in competing speech perception abilities develop throughout the school-age years, children already show a benefit from voice gender cue differences early on. Factors other than children's discrimination thresholds seem to relate more closely to their developing speech in competing speech perception abilities.

Aging Effects on Categorical Perception of Mandarin Lexical Tones in Noise

Purpose The purpose of this study was to examine the aging effects on the categorical perception (CP) of Mandarin lexical Tones 1-4 and Tones 1-2 in noise. It also investigated whether listeners' categorical tone perception in noise correlated with their general tone identification of 20 natural vowel-plus-tone signals in noise. Method Twelve younger and 12 older listeners with normal hearing were recruited in both tone identification and discrimination tasks in a CP paradigm where fundamental frequency contours of target stimuli varied systematically from the flat tone (Tone 1) to the rising/falling tones (Tones 2/4). Both tasks were conducted in quiet and noise with signal-to-noise ratios set at -5 and -10 dB, respectively, and general tone identification of natural speech signals was also tested in noise conditions. Results Compared with younger listeners, older listeners had shallower identification slopes and smaller discrimination peakedness in Tones 1-2/4 perception in all listening conditions, except for Tones 1-4 perception in quiet where no group differences were found. Meanwhile, noise affected Tones 1-2/4 perception: The signal-to-noise ratio condition at -10 dB brought shallower slope in Tones 1-2/4 identification and less peakedness in Tones 1-4 discrimination for both listener groups. Older listeners' CP in noise, the identification slopes in particular, positively correlated with their general tone identification in noise, but such correlations were partially missing for younger listeners. Conclusions Both aging and the presence of speech-shaped noise significantly reduced the CP of Mandarin Tones 1-2/4. Listeners' Mandarin tone recognition may be related to their CP of Mandarin tones.

Psychometric function for speech-in-noise tests accounts for word-recognition deficits in older listeners

Speech-in-noise (SIN) understanding in older age is affected by hearing loss, impaired central auditory processing, and cognitive deficits. SIN-tests measure these factors' compound effects by a speech reception threshold, defined as the signal-to-noise ratio required for 50% word understanding (SNR50). This study compared two standard SIN tests, QuickSIN (n = 354) in young and older adults and BKB-SIN (n = 139) in older adults (>60 years). The effects of hearing loss and age on SIN understanding were analyzed to identify auditory and nonauditory contributions to SIN loss. Word recognition in noise was modelled with individual psychometric functions using a logistic fit with three parameters: the midpoint (SNRα), slope (β), and asymptotic word-recognition deficit at high SNR (λ). The parameters SNRα and λ formally separate SIN loss into two components. SNRα characterizes the steep slope of the psychometric function at which a slight SNR increase provides a considerable improvement in SIN understanding. SNRα was discussed as being predominantly affected by audibility and low-level central auditory processing. The parameter λ describes a shallow segment of the psychometric function at which a further increase in the SNR provides modest improvement in SIN understanding. Cognitive factors in aging may contribute to the SIN loss indicated by λ.

Fundamental frequency range and other acoustic factors that might contribute to the clear-speech benefit

The main goal of the present study was to assess the role of the fundamental frequency (F0) range on the clear-speech benefit. Conversational- and clear-speech sentences were recorded for four male speakers: the speakers' clear-speech productions had slower speaking rates, wider F0 range, more high-frequency energy, expanded vowel space, and higher vocal intensity level relative to their conversational-speech productions. To examine if F0 range contributes to the clear-speech benefit, the F0 range of clear-speech sentences was compressed to match that of the speakers' conversational-speech sentences. Fifteen listeners were presented with conversational, clear, and F0-compressed sentences in sustained speech-shaped noise. All talkers elicited substantial intelligibility benefits (keyword percent correct) from clear and F0-compressed speech when compared with conversational speech. There was no significant difference in performance between clear and F0-compressed speech. These results leave open the possibility that a clear-speech benefit could be a result of its F0 contours rather than its wide F0 range. Intelligibility predictions based on acoustic characteristics of clear speech, specifically high-frequency emphasis and pauses, accounted for either small or negligible amounts of the clear-speech benefit.

Evaluation of Italian Simplified Matrix Test for Speech-Recognition Measurements in Noise

This study aimed at the evaluation of a simplified Italian matrix test (SiIMax) for speech-recognition measurements in noise for adults and children. Speech-recognition measurements with adults and children were conducted to examine the training effect and to establish reference speech-recognition thresholds of 50% (SRT50) and 80% (SRT80) correct responses. Test-list equivalency was evaluated only with adults. Twenty adults and 96 children—aged between 5 and 10 years—participated. Evaluation measurements with the adults confirmed the equivalence of the test lists, with a mean SRT50 of −8.0 dB and a standard deviation of 0.2 dB across the test lists. The test-specific slope (the average of the list-specific slopes) was 11.3%/dB, with a standard deviation of 0.6%/dB. For both adults and children, only one test list of 14 phrases needs to be presented to account for the training effect. For the adults, adaptive measurements of the SRT50 and SRT80 showed mean values of −7.0 ± 0.6 and −4.5 ± 1.1 dB, respectively. For children, a slight influence of age on the SRT was observed. The mean SRT50s were −5.6 ± 1.2, −5.8 ± 1.2 and −6.6 ± 1.3 dB for the children aged 5–6, 7–8 and 9–10 years, respectively. The corresponding SRT80s were −1.5 ± 2.7, −3.0 ± 1.7 and −3.7 ± 1.4 dB. High test–retest reliabilities of 1.0 and 1.1 dB for the SRT80 were obtained for the adults and children, respectively. This makes the test suitable for accurate and reliable speech-recognition measurements.

Does visual speech provide release from perceptual masking in children?

Adults benefit more from visual speech in speech maskers than in noise maskers because visual speech helps perceptually isolate target talkers from competing talkers. To investigate whether children use visual speech to perceptually isolate target talkers, this study compared children's speech recognition thresholds in auditory and audiovisual condition across two maskers: two-talker speech and noise. Children demonstrated similar audiovisual benefit in both maskers. Individual differences in speechreading accuracy predicted audiovisual benefit in each masker to a similar degree. Results suggest that although visual speech improves children's masked speech recognition thresholds, children may use visual speech in different ways than adults.

Performance of normal-hearing listeners on the Repeat-Recall test in different noise configurations

OBJECTIVE

This study measured the performance of normal-hearing listeners on the Repeat-Recall Test (RRT) in two noise types (2-talker babble [2TBN] and continuous speech-shaped noise [SSN]) by two noise azimuths (0° and 180°) configurations at signal-to-noise ratios (SNRs) of 0, 5, 10, and 15 dB and quiet.

DESIGN

Within-subject repeated measures.

STUDY SAMPLE

Twenty-one listeners with normal hearing who also passed cognitive screening were tested in the sound-field with the speech stimulus presented from 0° at 75 dB SPL in 4 noise configurations. The order of SNRs, noise configurations, and RRT topic conditions was counterbalanced across listeners.

RESULTS

Analysis revealed that repeat scores were significantly better for 2TBN, for noise at 180°, and for high context (HC) sentences. Recall performance was significantly better for SSN and HC sentences. Listening effort ratings were higher for SSN and for noise front condition at SNR ≤ 10 dB. The 2TBN noise was tolerated longer than SSN. Performance on all measures improved with SNRs.

CONCLUSIONS

These data showed performance differences among noise configurations and provided a preliminary basis for comparison with hearing-impaired listeners' performance on the RRT.

Yes/no and two-interval forced-choice tasks with listener-based vs observer-based responses

Observer-based procedures are used to assess auditory behavior in infants, often incorporating adaptive tracking algorithms. These procedures are reliable, but effects of modifications made to accommodate infant testing are not fully understood. One modification is that observation intervals are undefined for the listener, introducing signal-temporal uncertainty and increasing the likelihood that listener response bias will influence estimates of performance. The effect of these factors was evaluated by comparing threshold estimates obtained from adults using two tasks: (1) single-interval, yes/no and (2) two-interval, forced-choice. Detection thresholds were estimated adaptively for a 1000-Hz FM tone in quiet and for a word presented in two-talker speech masking. Trials were initiated and judged by the observer (observer-based) or the listener (listener-based). Thus, listening intervals were temporally uncertain in observer-based procedures and temporally defined in listener-based procedures. Thresholds were higher for observer-based relative to corresponding listener-based procedures. The magnitude of this difference was similar across the yes/no and two-interval tasks, and was larger for masked word detection than tone detection in quiet. Listeners adopted a conservative criterion when tested using the observer-based, yes/no procedure, but modeling results suggest that signal-temporal uncertainty accounts for the largest portion of the threshold difference between observer-based and listener-based procedures.

Development of the Everyday Conversational Sentences in Noise test

To capture the demands of real-world listening, laboratory-based speech-in-noise tasks must better reflect the types of speech and environments listeners encounter in everyday life. This article reports the development of original sentence materials that were produced spontaneously with varying vocal efforts. These sentences were extracted from conversations between a talker pair (female/male) communicating in different realistic acoustic environments to elicit normal, raised and loud vocal efforts. In total, 384 sentences were extracted to provide four equivalent lists of 16 sentences at the three efforts for the two talkers. The sentences were presented to 32 young, normally hearing participants in stationary noise at five signal-to-noise ratios from -8 to 0 dB in 2 dB steps. Psychometric functions were fitted for each sentence, revealing an average 50% speech reception threshold (SRT₅₀) of -5.2 dB, and an average slope of 17.2%/dB. Sentences were then level-normalised to adjust their individual SRT₅₀ to the mean (-5.2 dB). The sentences may be combined with realistic background noise to provide an assessment method that better captures the perceptual demands of everyday communication.

Correspondence Between Cognitive and Audiological Evaluations Among the Elderly: A Preliminary Report of an Audiological Screening Model of Subjects at Risk of Cognitive Decline With Slight to Moderate Hearing Loss

Epidemiological studies show increasing prevalence rates of cognitive decline and hearing loss with age, particularly after the age of 65 years. These conditions are reported to be associated, although conclusive evidence of causality and implications is lacking. Nevertheless, audiological and cognitive assessment among elderly people is a key target for comprehensive and multidisciplinary evaluation of the subject’s frailty status. To evaluate the use of tools for identifying older adults at risk of hearing loss and cognitive decline and to compare skills and abilities in terms of hearing and cognitive performances between older adults and young subjects, we performed a prospective cross-sectional study using supraliminal auditory tests. The relationship between cognitive assessment results and audiometric results was investigated, and reference ranges for different ages or stages of disease were determined. Patients older than 65 years with different degrees of hearing function were enrolled. Each subject underwent an extensive audiological assessment, including tonal and speech audiometry, Italian Matrix Sentence Test, and speech audiometry with logatomes in quiet. Cognitive function was screened and then verified by experienced clinicians using the Montreal Cognitive Assessment Score, the Geriatric Depression Scale, and further investigations in some. One hundred twenty-three subjects were finally enrolled during 2016–2019: 103 were >65 years of age and 20 were younger participants (as controls). Cognitive functions showed a correlation with the audiological results in post-lingual hearing-impaired patients, in particular in those affected by slight to moderate hearing loss and aged more than 70 years. Audiological testing can thus be useful in clinical assessment and identification of patients at risk of cognitive impairment. The study was limited by its sample size (CI 95%; CL 10%), strict dependence on language, and hearing threshold. Further investigations should be conducted to confirm the reported results and to verify similar screening models.

Impact of Background Noise Fluctuation and Reverberation on Response Time in a Speech Reception Task

Purpose This study examines the effects of reverberation and noise fluctuation on the response time (RT) to the auditory stimuli in a speech reception task. Method The speech reception task was presented to 76 young adults with normal hearing in 3 simulated listening conditions (1 anechoic, 2 reverberant). Speechlike stationary and fluctuating noise were used as maskers, in a wide range of signal-to-noise ratios. The speech-in-noise tests were presented in a closed-set format; data on speech intelligibility and RT (time elapsed from the offset of the auditory stimulus to the response selection) were collected. A slowing down in RTs was interpreted as an increase in listening effort. Results RTs slowed down in the more challenging signal-to-noise ratios, with increasing reverberation and for stationary compared to fluctuating noise, consistently with a fluctuating masking release scheme. When speech intelligibility was fixed, it was found that the estimated RTs were similar or faster for stationary compared to fluctuating noise, depending on the amount of reverberation. Conclusions The current findings add to the literature on listening effort for listeners with normal hearing by indicating that the addition of reverberation to fluctuating noise increases RT in a speech reception task. The results support the importance of integrating noise and reverberation to provide accurate predictors of real-world performance in clinical settings.

Auditory and Somatosensory Interaction in Speech Perception in Children and Adults

Multisensory integration (MSI) allows us to link sensory cues from multiple sources and plays a crucial role in speech development. However, it is not clear whether humans have an innate ability or whether repeated sensory input while the brain is maturing leads to efficient integration of sensory information in speech. We investigated the integration of auditory and somatosensory information in speech processing in a bimodal perceptual task in 15 young adults (age 19–30) and 14 children (age 5–6). The participants were asked to identify if the perceived target was the sound /e/ or /ø/. Half of the stimuli were presented under a unimodal condition with only auditory input. The other stimuli were presented under a bimodal condition with both auditory input and somatosensory input consisting of facial skin stretches provided by a robotic device, which mimics the articulation of the vowel /e/. The results indicate that the effect of somatosensory information on sound categorization was larger in adults than in children. This suggests that integration of auditory and somatosensory information evolves throughout the course of development.

The motor system's [modest] contribution to speech perception

Recent evidence suggests that the motor system may have a facilitatory role in speech perception during noisy listening conditions. Studies clearly show an association between activity in auditory and motor speech systems, but also hint at a causal role for the motor system in noisy speech perception. However, in the most compelling "causal" studies performance was only measured at a single signal-to-noise ratio (SNR). If listening conditions must be noisy to invoke causal motor involvement, then effects will be contingent on the SNR at which they are tested. We used articulatory suppression to disrupt motor-speech areas while measuring phonemic identification across a range of SNRs. As controls, we also measured phoneme identification during passive listening, mandible gesturing, and foot-tapping conditions. Two-parameter (threshold, slope) psychometric functions were fit to the data in each condition. Our findings indicate: (1) no effect of experimental task on psychometric function slopes; (2) a small effect of articulatory suppression, in particular, on psychometric function thresholds. The size of the latter effect was 1 dB (~5% correct) on average, suggesting, at best, a minor modulatory role of the speech motor system in perception.

Measuring Mandarin Speech Recognition Thresholds Using the Method of Adaptive Tracking

Purpose The purpose of this study was to examine (a) the psychometric functions of Mandarin speech-on-speech masking with a comparison to the psychometric properties of the English version and (b) the feasibility of using the method of adaptive tracking (MAT) to measure Mandarin speech recognition thresholds in different masker conditions using a Chinese coordinate response measure (C-CRM) speech corpus. Method The study followed the example of the English coordinate response measure (E-CRM) speech corpus and designed a Chinese version. Sixteen listeners were recruited for a monaural Mandarin speech recognition test using C-CRM materials in 5 competing speech masker conditions: 1-talker different-gender, 1-talker same-gender, and 2-, 4-, and 8-talker maskers. Both the MAT and the method of constant stimuli (MCS) were used and then compared. Results Results of the MCS revealed that Mandarin listeners' psychometric functions varied depending upon masker characteristics (e.g., the number and gender of talkers), because significant differences were suggested among the 5 masker conditions (mainly between 1-talker and multitalker), as measured in the slope b and the 50% threshold. Meanwhile, speech identification improved monotonically with increasing signal-to-noise ratios for all 5 masker conditions, except that a plateau was observed with signal-to-noise ratios from -10 to 0 dB in the 1-talker maskers. The properties of C-CRM psychometric functions largely agreed with E-CRM findings, and yet lower speech recognition thresholds were found in C-CRM. Meanwhile, the comparisons of the thresholds estimated in the MAT and the MCS showed no significant differences for all 5 masker conditions. Conclusion The results suggest that masker characteristics greatly affected Mandarin psychometric functions and monotonicity was present in all 5 C-CRM maskers, echoing the E-CRM literature in a great extent. Interestingly, target words of C-CRM were found easier to recognize in multitalker babbles than those of E-CRM. Moreover, comparisons of the MAT and the MCS suggest that the MAT provided a feasible method for measuring Mandarin speech recognition thresholds with the C-CRM speech maskers.

Evidence for enhanced neural tracking of the speech envelope underlying age-related speech-in-noise difficulties

When we grow older, understanding speech in noise becomes more challenging. Research has demonstrated the role of auditory temporal and cognitive deficits in these age-related speech-in-noise difficulties. To better understand the underlying neural mechanisms, we recruited young, middle-aged, and older normal-hearing adults and investigated the interplay between speech understanding, cognition, and neural tracking of the speech envelope using electroencephalography. The stimuli consisted of natural speech masked by speech-weighted noise or a competing talker and were presented at several subject-specific speech understanding levels. In addition to running speech, we recorded auditory steady-state responses at low modulation frequencies to assess the effect of age on nonspeech sounds. The results show that healthy aging resulted in a supralinear increase in the speech reception threshold, i.e., worse speech understanding, most pronounced for the competing talker. Similarly, advancing age was associated with a supralinear increase in envelope tracking, with a pronounced enhancement for older adults. Additionally, envelope tracking was found to increase with speech understanding, most apparent for older adults. Because we found that worse cognitive scores were associated with enhanced envelope tracking, our results support the hypothesis that enhanced envelope tracking in older adults is the result of a higher activation of brain regions for processing speech, compared with younger adults. From a cognitive perspective, this could reflect the inefficient use of cognitive resources, often observed in behavioral studies. Interestingly, the opposite effect of age was found for auditory steady-state responses, suggesting a complex interplay of different neural mechanisms with advancing age.NEW & NOTEWORTHY We measured neural tracking of the speech envelope across the adult lifespan and found a supralinear increase in envelope tracking with age. Using a more ecologically valid approach than auditory steady-state responses, we found that young and older, as well as middle-aged, normal-hearing adults showed an increase in envelope tracking with increasing speech understanding and that this association is stronger for older adults.

Psychometric function slope for speech-in-noise and speech-in-speech: Effects of development and aging

Masked sentence recognition was evaluated in normal-hearing children (8.8-10.5 years), young adults (18-28 years), and older adults (60-71 years). Consistent with published data, speech recognition thresholds were poorer for young children and older adults than for young adults, particularly when the masker was composed of speech. Psychometric function slopes were steeper for young children and older adults than for young adults when the masker was two-talker speech, but not when it was speech-shaped noise. Multiple factors are implicated in the age effects observed for speech-in-speech recognition at low signal-to-noise ratios.

An Analysis of Individual Differences in Recognizing Monosyllabic Words Under the Speech Intelligibility Index Framework

Individual differences in the recognition of monosyllabic words, either in isolation (NU6 test) or in sentence context (SPIN test), were investigated under the theoretical framework of the speech intelligibility index (SII). An adaptive psychophysical procedure, namely the quick-band-importance-function procedure, was developed to enable the fitting of the SII model to individual listeners. Using this procedure, the band importance function (i.e., the relative weights of speech information across the spectrum) and the link function relating the SII to recognition scores can be simultaneously estimated while requiring only 200 to 300 trials of testing. Octave-frequency band importance functions and link functions were estimated separately for NU6 and SPIN materials from 30 normal-hearing listeners who were naïve to speech recognition experiments. For each type of speech material, considerable individual differences in the spectral weights were observed in some but not all frequency regions. At frequencies where the greatest intersubject variability was found, the spectral weights were correlated between the two speech materials, suggesting that the variability in spectral weights reflected listener-originated factors.

Discrimination of Gain Increments in Speech-Shaped Noises

Frequency-dependent gain adjustments are routine in hearing-aid fittings, whether in matching to real-ear targets or fine-tuning to patient feedback. Patient feedback may be unreliable and fittings inefficient if adjustments are not discriminable. To examine what gain adjustments are discriminable, we measured the just-noticeable differences (JNDs) for level increments in speech-shaped noises processed with prescription gains. JNDs were measured in the better ears of 38 participants with hearing impairment using a fixed-level, same-different task. JNDs were measured for increments at six individual frequency-bands: a 0.25-kHz low-pass band; octave-wide bands at 0.5, 1, 2, and 4 kHz; and a 6-kHz high-pass band. JNDs for broadband increments were also measured. JNDs were estimated at d' of 1 for a minimally discriminable increment in optimal laboratory conditions. The JND for frequency-band increments was 2.8 dB excluding the 0.25-kHz low-pass band, for which the JND was 4.5 dB. The JND for broadband increments was 1.5 dB. Participants' median frequency-band and broadband JNDs were positively correlated. JNDs were mostly independent of age, pure-tone thresholds, and cognitive score. In consideration of self-fitting adjustments in noisier conditions, JNDs were additionally estimated at a more sensitive d' of 2. These JNDs were 6 dB for bands below 1 kHz, and 5 dB for bands at and above 1 kHz. Overall, the results suggest noticeable fine-tuning adjustments of 3 dB and self-fitting adjustments of 5 dB.

First-language raters' opinions when validating word recordings for a newly developed speech reception threshold test

Background

The purpose of this study was to consider the value of adding first-language speaker ratings to the process of validating word recordings for use in a new speech reception threshold (SRT) test in audiology. Previous studies had identified 28 word recordings as being suitable for use in a new SRT test. These word recordings had been shown to satisfy the linguistic criteria of familiarity, phonetic dissimilarity and tone, and the psychometric criterion of homogeneity of audibility.

Objectives

The aim of the study was to consider the value of adding first-language speakers’ ratings when validating word recordings for a new SRT test.

Method

A single observation, cross-sectional design was used to collect and analyse quantitative data in this study. Eleven first-language isiZulu speakers, purposively selected, were asked to rate each of the word recordings for pitch, clarity, naturalness, speech rate and quality on a 5-point Likert scale. The percent agreement and Friedman test were used for analysis.

Results

More than 20% of these 11 participants rated the three-word recordings below ‘strongly agree’ in the category of pitch or tone, and one-word recording below ‘strongly agree’ in the categories of pitch or tone, clarity or articulation and naturalness or dialect.

Conclusion

The first-language speaker ratings proved to be a valuable addition to the process of selecting word recordings for use in a new SRT test. In particular, these ratings identified potentially problematic word recordings in the new SRT test that had been missed by the previously and more commonly used linguistic and psychometric selection criteria.

Robust and efficient Bayesian adaptive psychometric function estimation

The efficient measurement of the threshold and slope of the psychometric function (PF) is an important objective in psychoacoustics. This paper proposes a procedure that combines a Bayesian estimate of the PF with either a look one-ahead or a look two-ahead method of selecting the next stimulus presentation. The procedure differs from previously proposed algorithms in two respects: (i) it does not require the range of possible PF parameters to be specified in advance and (ii) the sequence of probe signal-to-noise ratios optimizes the threshold and slope estimates at a performance level, ϕ, that can be chosen by the experimenter. Simulation results show that the proposed procedure is robust and that the estimates of both threshold and slope have a consistently low bias. Over a wide range of listener PF parameters, the root-mean-square errors after 50 trials were ∼1.2 dB in threshold and 0.14 in log-slope. It was found that the performance differences between the look one-ahead and look two-ahead methods were negligible and that an entropy-based criterion for selecting the next stimulus was preferred to a variance-based criterion.

Output signal-to-noise ratio and speech perception in noise: effects of algorithm

OBJECTIVE

The aims of this study were to: 1) quantify the amount of change in signal-to-noise ratio (SNR) as a result of compression and noise reduction (NR) processing in devices from three hearing aid (HA) manufacturers and 2) use the SNR changes to predict changes in speech perception. We hypothesised that the SNR change would differ across processing type and manufacturer, and that improvements in SNR would relate to improvements in performance.

DESIGN

SNR at the output of the HAs was quantified using a phase-inversion technique. A linear mixed model was used to determine whether changes in SNR across HA conditions were predictive of changes in aided speech perception in noise.

STUDY SAMPLE

Two groups participated: 25 participants had normal-hearing and 25 participants had mild to moderately severe sensorineural hearing loss.

RESULTS

The HAs programmed for both groups changed the SNR by a small, but statistically significant amount. Significant interactions in SNR changes were observed between HA devices and processing types. However, the change in SNR was not predictive of changes in speech perception.

CONCLUSION

Although observed significant changes in SNR resulting from compression and NR did not convert to changes in speech perception, these algorithms may serve other purposes.

On Detectable and Meaningful Speech-Intelligibility Benefits

The most important parameter that affects the ability to hear and understand speech in the presence of background noise is the signal-to-noise ratio (SNR). Despite decades of research in speech intelligibility, it is not currently known how much improvement in SNR is needed to provide a meaningful benefit to someone. We propose that the underlying psychophysical basis to a meaningful benefit should be the just noticeable difference (JND) for SNR. The SNR JND was measured in a series of experiments using both adaptive and fixed-level procedures across participants of varying hearing ability. The results showed an average SNR JND of approximately 3 dB for sentences in same-spectrum noise. The role of the stimulus and link to intelligibility was examined by measuring speech-intelligibility psychometric functions and comparing the intelligibility JND estimated from those functions with measured SNR JNDs. Several experiments were then conducted to establish a just meaningful difference (JMD) for SNR. SNR changes that could induce intervention-seeking behaviour for an individual were measured with subjective scaling and report, using the same stimuli as the SNR JND experiment as pre- and post-benefit examples. The results across different rating and willingness-to-change tasks showed that the mean ratings increased near linearly with a change in SNR, but a change of at least 6 dB was necessary to reliably motivate participants to seek intervention. The magnitude of the JNDs and JMDs for speech-intelligibility benefits measured here suggest a gap between what is achievable and what is meaningful.

Monaural speech intelligibility and detection in maskers with varying amounts of spectro-temporal speech features

Speech intelligibility is strongly affected by the presence of maskers. Depending on the spectro-temporal structure of the masker and its similarity to the target speech, different masking aspects can occur which are typically referred to as energetic, amplitude modulation, and informational masking. In this study speech intelligibility and speech detection was measured in maskers that vary systematically in the time-frequency domain from steady-state noise to a single interfering talker. Male and female target speech was used in combination with maskers based on speech for the same or different gender. Observed data were compared to predictions of the speech intelligibility index, extended speech intelligibility index, multi-resolution speech-based envelope-power-spectrum model, and the short-time objective intelligibility measure. The different models served as analysis tool to help distinguish between the different masking aspects. Comparison shows that overall masking can to a large extent be explained by short-term energetic masking. However, the other masking aspects (amplitude modulation an informational masking) influence speech intelligibility as well. Additionally, it was obvious that all models showed considerable deviations from the data. Therefore, the current study provides a benchmark for further evaluation of speech prediction models.

Speech intelligibility in rooms: Effect of prior listening exposure interacts with room acoustics

There is now converging evidence that a brief period of prior listening exposure to a reverberant room can influence speech understanding in that environment. Although the effect appears to depend critically on the amplitude modulation characteristic of the speech signal reaching the ear, the extent to which the effect may be influenced by room acoustics has not been thoroughly evaluated. This study seeks to fill this gap in knowledge by testing the effect of prior listening exposure or listening context on speech understanding in five different simulated sound fields, ranging from anechoic space to a room with broadband reverberation time (T60) of approximately 3 s. Although substantial individual variability in the effect was observed and quantified, the context effect was, on average, strongly room dependent. At threshold, the effect was minimal in anechoic space, increased to a maximum of 3 dB on average in moderate reverberation (T60 = 1 s), and returned to minimal levels again in high reverberation. This interaction suggests that the functional effects of prior listening exposure may be limited to sound fields with moderate reverberation (0.4 ≤ T60 ≤ 1 s).

The Just-Meaningful Difference in Speech-to-Noise Ratio

The speech-to-noise ratio (SNR) in an environment plays a vital role in speech communication for both normal-hearing (NH) and hearing-impaired (HI) listeners. While hearing-assistance devices attempt to deliver as favorable an SNR as possible, there may be discrepancies between noticeable and meaningful improvements in SNR. Furthermore, it is not clear how much of an SNR improvement is necessary to induce intervention-seeking behavior. Here, we report on a series of experiments examining the just-meaningful difference (JMD) in SNR. All experiments used sentences in same-spectrum noise, with two intervals on each trial mimicking examples of pre- and post-benefit situations. Different groups of NH and HI adults were asked (a) to rate how much better or worse the change in SNR was in a number of paired examples, (b) if they would swap the worse for the better SNR (e.g., their current device for another), or (c) if they would be willing to go to the clinic for the given increase in SNR. The mean SNR JMD based on better or worse ratings (one arbitrary unit) was similar to the just-noticeable difference, approximately 3 dB. However, the mean SNR JMD for the more clinically relevant tasks-willingness (at least 50% of the time) to swap devices or attend the clinic for a change in SNR--was 6 to 8 dB regardless of hearing ability. This SNR JMD of the order of 6 dB provides a new benchmark, indicating the SNR improvement necessary to immediately motivate participants to seek intervention.

Psychometric functions for sentence recognition in sinusoidally amplitude-modulated noises

Listeners' speech reception is better when speech is masked by a modulated masker compared to an unmodulated masker with the same long-term root-mean-square level. It has been suggested that listeners take advantage of brief periods of quiescence in a modulated masker to extract speech information. Two experiments examined the contribution of such "dip-listening" models. The first experiment estimated psychometric functions for speech intelligibility using sentences masked by sinusoidally modulated and unmodulated speech-shaped noises and the second experiment estimated detection thresholds for a tone pip added at the central dip in the masker. Modulation rates ranging from 1 to 64 Hz were tested. In experiment 1 the slopes of the psychometric functions were shallower for lower modulation rates and the pattern of speech reception thresholds as a function of modulation rate was nonmonotonic with a minimum near 16 Hz. In contrast, the detection thresholds from experiment 2 increased monotonically with modulation rate. The results suggest that the benefits of listening to speech in temporally fluctuating maskers cannot be solely ascribed to the temporal acuity of the auditory system.

Optimization of the Dutch matrix test by random selection of sentences from a preselected subset

Matrix tests are available for speech recognition testing in many languages. For an accurate measurement, a steep psychometric function of the speech materials is required. For existing tests, it would be beneficial if it were possible to further optimize the available materials by increasing the function's steepness. The objective is to show if the steepness of the psychometric function of an existing matrix test can be increased by selecting a homogeneous subset of recordings with the steepest sentence-based psychometric functions. We took data from a previous multicenter evaluation of the Dutch matrix test (45 normal-hearing listeners). Based on half of the data set, first the sentences (140 out of 311) with a similar speech reception threshold and with the steepest psychometric function (≥9.7%/dB) were selected. Subsequently, the steepness of the psychometric function for this selection was calculated from the remaining (unused) second half of the data set. The calculation showed that the slope increased from 10.2%/dB to 13.7%/dB. The resulting subset did not allow the construction of enough balanced test lists. Therefore, the measurement procedure was changed to randomly select the sentences during testing. Random selection may interfere with a representative occurrence of phonemes. However, in our material, the median phonemic occurrence remained close to that of the original test. This finding indicates that phonemic occurrence is not a critical factor. The work highlights the possibility that existing speech tests might be improved by selecting sentences with a steep psychometric function.

The just-noticeable difference in speech-to-noise ratio

Just-noticeable differences (JNDs) have been measured for various features of sounds, but despite its importance to communication, there is no benchmark for what is a just-noticeable-and possibly meaningful-difference in speech-to-noise ratio (SNR). SNR plays a crucial role in speech communication for normal-hearing and hearing-impaired listeners. Difficulty hearing speech in background noise-a poor SNR-often leads to dissatisfaction with hearing-assistance devices. While such devices attempt through various strategies to address this problem, it is not currently known how much improvement in SNR is needed to provide a noticeable benefit. To investigate what is a noticeable benefit, we measured the JND in SNR for both normal-hearing and hearing-impaired listeners. Here, we report the SNR JNDs of 69 participants of varying hearing ability, estimated using either an adaptive or fixed-level procedure. The task was to judge which of the two intervals containing a sentence in speech-spectrum noise presented over headphones was clearer. The level of each interval was roved to reduce the influence of absolute level cues. The results of both procedures showed an average SNR JND of 3 dB that was independent of hearing ability. Further experiments using a subset of normal-hearing listeners showed that level roving does elevate threshold. These results suggest that noise reduction schemes may need to achieve a benefit greater than 3 dB to be reliably discriminable.