Predictors of Susceptibility to Noise and Speech Masking Among School-Age Children With Hearing Loss or Typical Hearing.

OBJECTIVES: The purpose of this study was to evaluate effects of masker type and hearing group on the relationship between school-age children's speech recognition and age, vocabulary, working memory, and selective attention. This study also explored effects of masker type and hearing group on the time course of maturation of masked speech recognition. DESIGN: Participants included 31 children with normal hearing (CNH) and 41 children with mild to severe bilateral sensorineural hearing loss (CHL), between 6.7 and 13 years of age. Children with hearing aids used their personal hearing aids throughout testing. Audiometric thresholds and standardized measures of vocabulary, working memory, and selective attention were obtained from each child, along with masked sentence recognition thresholds in a steady state, speech-spectrum noise (SSN) and in a two-talker speech masker (TTS). Aided audibility through children's hearing aids was calculated based on the Speech Intelligibility Index (SII) for all children wearing hearing aids. Linear mixed effects models were used to examine the contribution of group, age, vocabulary, working memory, and attention to individual differences in speech recognition thresholds in each masker. Additional models were constructed to examine the role of aided audibility on masked speech recognition in CHL. Finally, to explore the time course of maturation of masked speech perception, linear mixed effects models were used to examine interactions between age, masker type, and hearing group as predictors of masked speech recognition. RESULTS: Children's thresholds were higher in TTS than in SSN. There was no interaction of hearing group and masker type. CHL had higher thresholds than CNH in both maskers. In both hearing groups and masker types, children with better vocabularies had lower thresholds. An interaction of hearing group and attention was observed only in the TTS. Among CNH, attention predicted thresholds in TTS. Among CHL, vocabulary and aided audibility predicted thresholds in TTS. In both maskers, thresholds decreased as a function of age at a similar rate in CNH and CHL. CONCLUSIONS: The factors contributing to individual differences in speech recognition differed as a function of masker type. In TTS, the factors contributing to individual difference in speech recognition further differed as a function of hearing group. Whereas attention predicted variance for CNH in TTS, vocabulary and aided audibility predicted variance in CHL. CHL required a more favorable signal to noise ratio (SNR) to recognize speech in TTS than in SSN (mean = +1 dB in TTS, -3 dB in SSN). We posit that failures in auditory stream segregation limit the extent to which CHL can recognize speech in a speech masker. Larger sample sizes or longitudinal data are needed to characterize the time course of maturation of masked speech perception in CHL.

Development of the Children's English and Spanish Speech Recognition Test: Psychometric Properties, Feasibility, Reliability, and Normative Data.

OBJECTIVES: The Children's English and Spanish Speech Recognition (ChEgSS) test is a computer-based tool for assessing closed-set word recognition in English and in Spanish, with a masker that is either speech-shaped noise or competing speech. The present study was conducted to (1) characterize the psychometric properties of the ChEgSS test, (2) evaluate feasibility and reliability for a large cohort of Spanish/English bilingual children with normal hearing, and (3) establish normative data. DESIGN: Three experiments were conducted to evaluate speech perception in children (4-17 years) and adults (19-40 years) with normal hearing using the ChEgSS test. In Experiment 1, data were collected from Spanish/English bilingual and English monolingual adults at multiple, fixed signal-to-noise ratios. Psychometric functions were fitted to the word-level data to characterize variability across target words in each language and in each masker condition. In Experiment 2, Spanish/English bilingual adults were tested using an adaptive tracking procedure to evaluate the influence of different target-word normalization approaches on the reliability of estimates of masked-speech recognition thresholds corresponding to 70.7% correct word recognition and to determine the optimal number of reversals needed to obtain reliable estimates. In Experiment 3, Spanish/English bilingual and English monolingual children completed speech perception testing using the ChEgSS test to (1) characterize feasibility across age and language group, (2) evaluate test-retest reliability, and (3) establish normative data. RESULTS: Experiments 1 and 2 yielded data that are essential for stimulus normalization, optimizing threshold estimation procedures, and interpreting threshold data across test language and masker type. Findings obtained from Spanish/English bilingual and English monolingual children with normal hearing in Experiment 3 support feasibility and demonstrate reliability for use with children as young as 4 years of age. Equivalent results for testing in English and Spanish were observed for Spanish/English bilingual children, contingent on adequate proficiency in the target language. Regression-based threshold norms were established for Spanish/English bilingual and English monolingual children between 4 and 17 years of age. CONCLUSIONS: The present findings indicate the ChEgSS test is appropriate for testing a wide age range of children with normal hearing in either Spanish, English, or both languages. The ChEgSS test is currently being evaluated in a large cohort of patients with hearing loss at pediatric audiology clinics across the United States. Results will be compared with normative data established in the present study and with established clinical measures used to evaluate English- and Spanish-speaking children. Questionnaire data from parents and clinician feedback will be used to further improve test procedures.

Effects of Stimulus Type on 16-kHz Detection Thresholds.

OBJECTIVES: Audiometric testing typically does not include frequencies above 8 kHz. However, recent research suggests that extended high-frequency (EHF) sensitivity could affect hearing in natural communication environments. Clinical assessment of hearing often employs pure tones and frequency-modulated (FM) tones interchangeably regardless of frequency. The present study was designed to evaluate how the stimulus chosen to measure EHF thresholds affects estimates of hearing sensitivity. DESIGN: The first experiment used standard audiometric procedures to measure 8- and 16-kHz thresholds for 5- to 28-year olds with normal hearing in the standard audiometric range (250 to 8000 Hz). Stimuli were steady tones, pulsed tones, and FM tones. The second experiment tested 18- to 28-year olds with normal hearing in the standard audiometric range using psychophysical procedures to evaluate how changes in sensitivity as a function of frequency affect detection of stimuli that differ with respect to bandwidth, including bands of noise. Thresholds were measured using steady tones, pulsed tones, FM tones, narrow bands of noise, and one-third-octave bands of noise at a range of center frequencies in one ear. RESULTS: In experiment 1, thresholds improved with increasing age at 8 kHz and worsened with increasing age at 16 kHz. Thresholds for individual participants were relatively similar for steady, pulsed, and FM tones at 8 kHz. At 16 kHz, mean thresholds were approximately 5 dB lower for FM tones than for steady or pulsed tones. This stimulus effect did not differ as a function of age. Experiment 2 replicated this greater stimulus effect at 16 kHz than at 8 kHz and showed that the slope of the audibility curve accounted for these effects. CONCLUSIONS: Contrary to prior expectations, there was no evidence that the choice of stimulus type affected school-age children more than adults. For individual participants, audiometric thresholds at 16 kHz were as much as 20 dB lower for FM tones than for steady tones. Threshold differences across stimuli at 16 kHz were predicted by differences in audibility across frequency, which can vary markedly between listeners. These results highlight the importance of considering spectral width of the stimulus used to evaluate EHF thresholds.

Speech-in-speech recognition in preschoolers.

OBJECTIVE: The purpose of this study was to 1) characterise word recognition in a speech masker for preschoolers tested using closed-set, forced-choice procedures and 2) better understand the stimulus and listener factors affecting performance. DESIGN: Speech recognition thresholds (SRTs) in a two-talker masker were evaluated using a picture-pointing response with two sets of disyllabic target words. ChEgSS words were previously developed for children ≥5 years of age, and simple words were developed for preschoolers. Familiarisation ensured accurate identification of target words before testing. STUDY SAMPLE: Participants were 3- and 4-year olds (n = 21) and young adults (n = 10) with normal hearing. RESULTS: Preschoolers and adults had significantly lower SRTs for the simple words than the ChEgSS words, and lower SRTs for early-acquired than later-acquired ChEgSS words. For both word sets, SRTs were approximately 11-dB higher for preschoolers than adults, and child age was associated with SRTs. Preschoolers' receptive vocabulary size predicted performance for ChEgSS words but not simple words. CONCLUSIONS: Preschoolers were more susceptible to speech-in-speech masking than adults, with a similar child-adult difference for the ChEgSS and simple words. Effects of receptive vocabulary in preschoolers' recognition of ChEgSS words indicate that vocabulary size is an important consideration, even when using closed-set methods.

"I think it impacts all areas of his life": Perspectives on hearing from mothers of individuals with Down syndrome.

BACKGROUND: Individuals with Down syndrome are known to have high rates of hearing loss, but it is unclear how this impacts their ability to communicate and function in real-world environments. METHODS: Sixteen English-speaking and Spanish-speaking mothers of individuals with Down syndrome ages 6-40 years participated in individual, semi-structured interviews using a videoconferencing platform. Session transcripts were analysed using applied thematic analysis. RESULTS: Mothers described listening environments, the impact of hearing on daily life, barriers to successful listening, and strategies to overcome communication barriers for their children with Down syndrome. CONCLUSIONS: Hearing was largely discussed in terms of challenges and detriments, suggesting that hearing experiences are predominately considered to negatively impact the functional abilities of individuals with Down syndrome. Background noise and hearing loss were sources of communication difficulties. Parent-reported barriers and strategies can inform ecologically valid research priorities aimed at improving outcomes for individuals with Down syndrome.

Effects of Hearing Loss on School-Aged Children's Ability to Benefit From F0 Differences Between Target and Masker Speech.

OBJECTIVES: The objectives of the study were to (1) evaluate the impact of hearing loss on children's ability to benefit from F0 differences between target/masker speech in the context of aided speech-in-speech recognition and (2) to determine whether compromised F0 discrimination associated with hearing loss predicts F0 benefit in individual children. We hypothesized that children wearing appropriately fitted amplification would benefit from F0 differences, but they would not show the same magnitude of benefit as children with normal hearing. Reduced audibility and poor suprathreshold encoding that degrades frequency discrimination were expected to impair children's ability to segregate talkers based on F0. DESIGN: Listeners were 9 to 17 year olds with bilateral, symmetrical, sensorineural hearing loss ranging in degree from mild to severe. A four-alternative, forced-choice procedure was used to estimate thresholds for disyllabic word recognition in a 60-dB-SPL two-talker masker. The same male talker produced target and masker speech. Target words had either the same mean F0 as the masker or were digitally shifted higher than the masker by three, six, or nine semitones. The F0 benefit was defined as the difference in thresholds between the shifted-F0 conditions and the unshifted-F0 condition. Thresholds for discriminating F0 were also measured, using a three-alternative, three-interval forced choice procedure, to determine whether compromised sensitivity to F0 differences due to hearing loss would predict children's ability to benefit from F0. Testing was performed in the sound field, and all children wore their personal hearing aids at user settings. RESULTS: Children with hearing loss benefited from an F0 difference of nine semitones between target words and masker speech, with older children generally benefitting more than younger children. Some children benefitted from an F0 difference of six semitones, but this was not consistent across listeners. Thresholds for discriminating F0 improved with increasing age and predicted F0 benefit in the nine-semitone condition. An exploratory analysis indicated that F0 benefit was not significantly correlated with the four-frequency pure-tone average (0.5, 1, 2, and 4 kHz), aided audibility, or consistency of daily hearing aid use, although there was a trend for an association with the low-frequency pure-tone average (0.25 and 0.5 kHz). Comparisons of the present data to our previous study of children with normal hearing demonstrated that children with hearing loss benefitted less than children with normal hearing for the F0 differences tested. CONCLUSIONS: The results demonstrate that children with mild-to-severe hearing loss who wear hearing aids benefit from relatively large F0 differences between target and masker speech during aided speech-in-speech recognition. The size of the benefit increases with increasing age, consistent with previously reported age effects for children with normal hearing. However, hearing loss reduces children's ability to capitalize on F0 differences between talkers. Audibility alone does not appear to be responsible for this effect; aided audibility and degree of loss were not primary predictors of performance. The ability to benefit from F0 differences may be limited by immature central processing or aspects of peripheral encoding that are not characterized in standard clinical assessments.

Contribution of Stimulus Variability to Word Recognition in Noise Versus Two-Talker Speech for School-Age Children and Adults.

BACKGROUND: Speech-in-speech recognition scores tend to be more variable than the speech-in-noise recognition scores, both within and across listeners. This variability could be due to listener factors, such as individual differences in audibility or susceptibility to informational masking. It could also be due to stimulus variability, with some speech-in-speech samples posing more of a challenge than others. The purpose of this experiment was to test two hypotheses: (1) that stimulus variability affects adults' word recognition in a two-talker speech masker and (2) that stimulus variability plays a smaller role in children's performance due to relatively greater contributions of listener factors. METHODS: Listeners were children (5 to 10 years) and adults (18 to 41 years) with normal hearing. Target speech was a corpus of 30 disyllabic words, each associated with an unambiguous illustration. Maskers were 30 samples of either two-talker speech or speech-shaped noise. The task was a four-alternative forced choice. Speech reception thresholds were measured adaptively, and those results were used to determine the signal-to-noise ratio associated with ≈65% correct for each listener and masker. Two 30-word blocks of fixed-level testing were then completed in each of the two conditions: (1) with the target-masker pairs randomly assigned prior to each block and (2) with frozen target-masker pairs. RESULTS: Speech reception thresholds were lower for adults than for children, particularly for the two-talker speech masker. Listener responses in fixed-level testing were evaluated for consistency across listeners. Target sample was the best predictor of performance in the speech-shaped noise masker for both the random and frozen conditions. In contrast, both the target and masker samples affected performance in the two-talker masker. Results were qualitatively similar for children and adults, and the pattern of performance across stimulus samples was consistent, with differences in masked target audibility in both age groups. CONCLUSIONS: Although word recognition in speech-shaped noise differed consistently across target words, recognition in a two-talker speech masker depended on both the target and masker samples. These stimulus effects are broadly consistent with a simple model of masked target audibility. Although variability in speech-in-speech recognition is often thought to reflect differences in informational masking, the present results suggest that variability in energetic masking across stimuli can play an important role in performance.

Masking Release for Speech-in-Speech Recognition Due to a Target/Masker Sex Mismatch in Children With Hearing Loss.

OBJECTIVES: The goal of the present study was to compare the extent to which children with hearing loss and children with normal hearing benefit from mismatches in target/masker sex in the context of speech-in-speech recognition. It was hypothesized that children with hearing loss experience a smaller target/masker sex mismatch benefit relative to children with normal hearing due to impairments in peripheral encoding, variable access to high-quality auditory input, or both. DESIGN: Eighteen school-age children with sensorineural hearing loss (7 to 15 years) and 18 age-matched children with normal hearing participated in this study. Children with hearing loss were bilateral hearing aid users. Severity of hearing loss ranged from mild to severe across participants, but most had mild to moderate hearing loss. Speech recognition thresholds for disyllabic words presented in a two-talker speech masker were estimated in the sound field using an adaptive, forced-choice procedure with a picture-pointing response. Participants were tested in each of four conditions: (1) male target speech/two-male-talker masker; (2) male target speech/two-female-talker masker; (3) female target speech/two-female-talker masker; and (4) female target speech/two-male-talker masker. Children with hearing loss were tested wearing their personal hearing aids at user settings. RESULTS: Both groups of children showed a sex-mismatch benefit, requiring a more advantageous signal to noise ratio when the target and masker were matched in sex than when they were mismatched. However, the magnitude of sex-mismatch benefit was significantly reduced for children with hearing loss relative to age-matched children with normal hearing. There was no effect of child age on the magnitude of sex-mismatch benefit. The sex-mismatch benefit was larger for male target speech than for female target speech. For children with hearing loss, the magnitude of sex-mismatch benefit was not associated with degree of hearing loss or aided audibility. CONCLUSIONS: The findings from the present study indicate that children with sensorineural hearing loss are able to capitalize on acoustic differences between speech produced by male and female talkers when asked to recognize target words in a competing speech masker. However, children with hearing loss experienced a smaller benefit relative to their peers with normal hearing. No association between the sex-mismatch benefit and measures of unaided thresholds or aided audibility were observed for children with hearing loss, suggesting that reduced peripheral encoding is not the only factor responsible for the smaller sex-mismatch benefit relative to children with normal hearing.

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.

Developmental Effects in Children's Ability to Benefit From F0 Differences Between Target and Masker Speech.

OBJECTIVES: The objectives of this study were to (1) evaluate the extent to which school-age children benefit from fundamental frequency (F0) differences between target words and competing two-talker speech, and (2) assess whether this benefit changes with age. It was predicted that while children would be more susceptible to speech-in-speech masking compared to adults, they would benefit from differences in F0 between target and masker speech. A second experiment was conducted to evaluate the relationship between frequency discrimination thresholds and the ability to benefit from target/masker differences in F0. DESIGN: Listeners were children (5 to 15 years) and adults (20 to 36 years) with normal hearing. In the first experiment, speech reception thresholds (SRTs) for disyllabic words were measured in a continuous, 60-dB SPL two-talker speech masker. The same male talker produced both the target and masker speech (average F0 = 120 Hz). The level of the target words was adaptively varied to estimate the level associated with 71% correct identification. The procedure was a four-alternative forced-choice with a picture-pointing response. Target words either had the same mean F0 as the masker or it was shifted up by 3, 6, or 9 semitones. To determine the benefit of target/masker F0 separation on word recognition, masking release was computed by subtracting thresholds in each shifted-F0 condition from the threshold in the unshifted-F0 condition. In the second experiment, frequency discrimination thresholds were collected for a subset of listeners to determine whether sensitivity to F0 differences would be predictive of SRTs. The standard was the syllable /ba/ with an F0 of 250 Hz; the target stimuli had a higher F0. Discrimination thresholds were measured using a three-alternative, three-interval forced choice procedure. RESULTS: Younger children (5 to 12 years) had significantly poorer SRTs than older children (13 to 15 years) and adults in the unshifted-F0 condition. The benefit of F0 separations generally increased with increasing child age and magnitude of target/masker F0 separation. For 5- to 7-year-olds, there was a small benefit of F0 separation in the 9-semitone condition only. For 8- to 12-year-olds, there was a benefit from both 6- and 9-semitone separations, but to a lesser degree than what was observed for older children (13 to 15 years) and adults, who showed a substantial benefit in the 6- and 9-semitone conditions. Examination of individual data found that children younger than 7 years of age did not benefit from any of the F0 separations tested. Results for the frequency discrimination task indicated that, while there was a trend for improved thresholds with increasing age, these thresholds were not predictive of the ability to use F0 differences in the speech-in-speech recognition task after controlling for age. CONCLUSIONS: The overall pattern of results suggests that children's ability to benefit from F0 differences in speech-in-speech recognition follows a prolonged developmental trajectory. Younger children are less able to capitalize on differences in F0 between target and masker speech. The extent to which individual children benefitted from target/masker F0 differences was not associated with their frequency discrimination thresholds.

Masked Sentence Recognition in Children, Young Adults, and Older Adults: Age-Dependent Effects of Semantic Context and Masker Type.

OBJECTIVES: Masked speech recognition in normal-hearing listeners depends in part on masker type and semantic context of the target. Children and older adults are more susceptible to masking than young adults, particularly when the masker is speech. Semantic context has been shown to facilitate noise-masked sentence recognition in all age groups, but it is not known whether age affects a listener's ability to use context with a speech masker. The purpose of the present study was to evaluate the effect of masker type and semantic context of the target as a function of listener age. DESIGN: Listeners were children (5 to 16 years), young adults (19 to 30 years), and older adults (67 to 81 years), all with normal or near-normal hearing. Maskers were either speech-shaped noise or two-talker speech, and targets were either semantically correct (high context) sentences or semantically anomalous (low context) sentences. RESULTS: As predicted, speech reception thresholds were lower for young adults than either children or older adults. Age effects were larger for the two-talker masker than the speech-shaped noise masker, and the effect of masker type was larger in children than older adults. Performance tended to be better for targets with high than low semantic context, but this benefit depended on age group and masker type. In contrast to adults, children benefitted less from context in the two-talker speech masker than the speech-shaped noise masker. Context effects were small compared with differences across age and masker type. CONCLUSIONS: Different effects of masker type and target context are observed at different points across the lifespan. While the two-talker masker is particularly challenging for children and older adults, the speech masker may limit the use of semantic context in children but not adults.

Amplitude modulation detection and modulation masking in school-age children and adults.

Two experiments were performed to better understand on- and off-frequency modulation masking in normal-hearing school-age children and adults. Experiment 1 estimated thresholds for detecting 16-, 64- or 256-Hz sinusoidal amplitude modulation (AM) imposed on a 4300-Hz pure tone. Thresholds tended to improve with age, with larger developmental effects for 64- and 256-Hz AM than 16-Hz AM. Detection of 16-Hz AM was also measured with a 1000-Hz off-frequency masker tone carrying 16-Hz AM. Off-frequency modulation masking was larger for younger than older children and adults when the masker was gated with the target, but not when the masker was continuous. Experiment 2 measured detection of 16- or 64-Hz sinusoidal AM carried on a bandpass noise with and without additional on-frequency masker AM. Children and adults demonstrated modulation masking with similar tuning to modulation rate. Rate-dependent age effects for AM detection on a pure-tone carrier are consistent with maturation of temporal resolution, an effect that may be obscured by modulation masking for noise carriers. Children were more susceptible than adults to off-frequency modulation masking for gated stimuli, consistent with maturation in the ability to listen selectively in frequency, but the children were not more susceptible to on-frequency modulation masking than adults.

The effect of target/masker fundamental frequency contour similarity on masked-speech recognition.

Greater informational masking is observed when the target and masker speech are more perceptually similar. Fundamental frequency (f0) contour, or the dynamic movement of f0, is thought to provide cues for segregating target speech presented in a speech masker. Most of the data demonstrating this effect have been collected using digitally modified stimuli. Less work has been done exploring the role of f0 contour for speech-in-speech recognition when all of the stimuli have been produced naturally. The goal of this project was to explore the importance of target and masker f0 contour similarity by manipulating the speaking style of talkers producing the target and masker speech streams. Sentence recognition thresholds were evaluated for target and masker speech that was produced with either flat, normal, or exaggerated speaking styles; performance was also measured in speech spectrum shaped noise and for conditions in which the stimuli were processed through an ideal-binary mask. Results confirmed that similarities in f0 contour depth elevated speech-in-speech recognition thresholds; however, when the target and masker had similar contour depths, targets with normal f0 contours were more resistant to masking than targets with flat or exaggerated contours. Differences in energetic masking across stimuli cannot account for these results.

Developmental Effects in Masking Release for Speech-in-Speech Perception Due to a Target/Masker Sex Mismatch.

OBJECTIVES: The purpose of this study was to evaluate the extent to which infants, school-age children, and adults benefit from a target/masker sex mismatch in the context of speech detection or recognition in a background of 2 competing talkers. It was hypothesized that the ability to benefit from a target/masker sex mismatch develops between infancy and the early school-age years, as children gain listening experience in multi-talker environments. DESIGN: Listeners were infants (7 to 13 months), children (5 to 10 years), and adults (18 to 33 years) with normal hearing. A series of five experiments compared speech detection or recognition in continuous two-talker speech across target/masker conditions that were sex matched or sex mismatched. In experiments 1 and 2, an observer-based, single-interval procedure was used to estimate speech detection thresholds for a spondaic word in a two-talker speech masker. In experiments 3 and 4, speech recognition thresholds were estimated in continuous two-talker speech using a four-alternative, forced-choice procedure. In experiment 5, speech reception thresholds (SRTs) were estimated for adults using the forced-choice recognition procedure after ideal time-frequency segregation processing was applied to the stimuli. RESULTS: Speech detection thresholds for adults tested in experiments 1 and 2 were significantly higher when the target word and speech masker were matched in sex than when they were mismatched, but thresholds for infants were similar across sex-matched and sex-mismatched conditions. Results for experiments 3 and 4 showed that school-age children and adults benefit from a target/masker sex mismatch for a forced-choice word recognition task. Children, however, obtained greater benefit than adults in 1 condition, perhaps due to greater susceptibility to masking overall. In experiment 5, adults had substantial threshold reductions and more uniform performance across the 4 conditions evaluated in experiments 3 and 4 after the application of ideal time-frequency segregation to the stimuli. CONCLUSIONS: The pattern of results observed across experiments suggests that the ability to take advantage of differences in vocal characteristics typically found between speech produced by male and female talkers develops between infancy and the school-age years. Considerable child-adult differences in susceptibility to speech-in-speech masking were observed for school-age children as old as 11 years of age in both sex-matched and sex-mismatched conditions.

Speech recognition for school-age children and adults tested in multi-tone vs multi-noise-band maskers.

The present study set out to test whether greater susceptibility to modulation masking could be responsible for immature recognition of speech in noise for school-age children. Listeners were normal-hearing four- to ten-year-olds and adults. Target sentences were filtered into 28 adjacent narrow bands (100-7800 Hz), and the masker was either spectrally matched noise bands or tones centered on each of the speech bands. In experiment 1, odd- and even-numbered bands of target-plus-masker were presented to opposite ears. Performance improved with child age in all conditions, but this improvement was larger for the multi-tone than the multi-noise-band masker. This outcome is contrary to the expectation that children are more susceptible than adults to masking produced by inherent modulation of the noise masker. In experiment 2, odd-numbered bands were presented to both ears, with the masker diotic and the target either diotic or binaurally out of phase. The binaural difference cue was particularly beneficial for young children tested in the multi-tone masker, suggesting that development of auditory stream segregation may play a role in the child-adult difference for this condition. Overall, results provide no evidence of greater susceptibility to modulation masking in children than adults.

Spatial Release From Masking in Children: Effects of Simulated Unilateral Hearing Loss.

OBJECTIVES: The purpose of this study was twofold: (1) to determine the effect of an acute simulated unilateral hearing loss on children's spatial release from masking in two-talker speech and speech-shaped noise, and (2) to develop a procedure to be used in future studies that will assess spatial release from masking in children who have permanent unilateral hearing loss. There were three main predictions. First, spatial release from masking was expected to be larger in two-talker speech than in speech-shaped noise. Second, simulated unilateral hearing loss was expected to worsen performance in all listening conditions, but particularly in the spatially separated two-talker speech masker. Third, spatial release from masking was expected to be smaller for children than for adults in the two-talker masker. DESIGN: Participants were 12 children (8.7 to 10.9 years) and 11 adults (18.5 to 30.4 years) with normal bilateral hearing. Thresholds for 50%-correct recognition of Bamford-Kowal-Bench sentences were measured adaptively in continuous two-talker speech or speech-shaped noise. Target sentences were always presented from a loudspeaker at 0° azimuth. The masker stimulus was either co-located with the target or spatially separated to +90° or -90° azimuth. Spatial release from masking was quantified as the difference between thresholds obtained when the target and masker were co-located and thresholds obtained when the masker was presented from +90° or -90° azimuth. Testing was completed both with and without a moderate simulated unilateral hearing loss, created with a foam earplug and supra-aural earmuff. A repeated-measures design was used to compare performance between children and adults, and performance in the no-plug and simulated-unilateral-hearing-loss conditions. RESULTS: All listeners benefited from spatial separation of target and masker stimuli on the azimuth plane in the no-plug listening conditions; this benefit was larger in two-talker speech than in speech-shaped noise. In the simulated-unilateral-hearing-loss conditions, a positive spatial release from masking was observed only when the masker was presented ipsilateral to the simulated unilateral hearing loss. In the speech-shaped noise masker, spatial release from masking in the no-plug condition was similar to that obtained when the masker was presented ipsilateral to the simulated unilateral hearing loss. In contrast, in the two-talker speech masker, spatial release from masking in the no-plug condition was much larger than that obtained when the masker was presented ipsilateral to the simulated unilateral hearing loss. When either masker was presented contralateral to the simulated unilateral hearing loss, spatial release from masking was negative. This pattern of results was observed for both children and adults, although children performed more poorly overall. CONCLUSIONS: Children and adults with normal bilateral hearing experience greater spatial release from masking for a two-talker speech than a speech-shaped noise masker. Testing in a two-talker speech masker revealed listening difficulties in the presence of disrupted binaural input that were not observed in a speech-shaped noise masker. This procedure offers promise for the assessment of spatial release from masking in children with permanent unilateral hearing loss.

Development of frequency discrimination at 250 Hz is similar for tone and /ba/ stimuli.

Frequency discrimination was measured in 5- to 11-year-olds and adults with normal hearing. The standard stimulus was either a 250-Hz tone or the syllable /ba/ with a fundamental frequency (F0) of 250 Hz. Target stimuli were higher in frequency than the standard, and the threshold for frequency discrimination was determined adaptively for each of the two stimulus types separately. For both the tone and /ba/ stimuli, thresholds improved approximately linearly with the log of child age, reaching adult levels by 11.5 years of age. There was no evidence of an effect of stimulus type.

Speech recognition in one- and two-talker maskers in school-age children and adults: Development of perceptual masking and glimpsing.

Children perform more poorly than adults on a wide range of masked speech perception paradigms, but this effect is particularly pronounced when the masker itself is also composed of speech. The present study evaluated two factors that might contribute to this effect: the ability to perceptually isolate the target from masker speech, and the ability to recognize target speech based on sparse cues (glimpsing). Speech reception thresholds (SRTs) were estimated for closed-set, disyllabic word recognition in children (5-16 years) and adults in a one- or two-talker masker. Speech maskers were 60 dB sound pressure level (SPL), and they were either presented alone or in combination with a 50-dB-SPL speech-shaped noise masker. There was an age effect overall, but performance was adult-like at a younger age for the one-talker than the two-talker masker. Noise tended to elevate SRTs, particularly for older children and adults, and when summed with the one-talker masker. Removing time-frequency epochs associated with a poor target-to-masker ratio markedly improved SRTs, with larger effects for younger listeners; the age effect was not eliminated, however. Results were interpreted as indicating that development of speech-in-speech recognition is likely impacted by development of both perceptual masking and the ability recognize speech based on sparse cues.

Masked Speech Perception Thresholds in Infants, Children, and Adults.

OBJECTIVE: The primary goal of this study was to compare infants' susceptibility to making produced by a two-talker speech and a speech-shaped noise masker. It is well documented that school-age children experience more difficulty recognizing speech embedded in two-talker speech than spectrally matched noise, a result attributed to immaturity in the ability to segregate target from masker speech, and/or to selectively attend to the target while disregarding the perceptually similar speech masker. However, findings from infant psychophysical studies suggest that infants are susceptible to auditory masking even when target and competing sounds are acoustically distinct. DESIGN: Listeners were infants (8 to10 months), children (8 to 10 years), and adults (18 to 33 years). The task was an observer-based, single-interval disyllabic word detection, in the presence of either a speech-shaped noise or a two-talker masker. The masker played continuously at 55 dB SPL, and the target level was adapted to estimate threshold. RESULTS: As observed previously for closed-set consonant and word identification as well as open-set word and sentence recognition, school-age children experienced relatively more masking than adults in the two-talker than the speech-shaped noise masker. The novel result of this study was that infants' speech detection thresholds were about 24 dB higher than those of adults in both maskers. While response bias differed between listener groups, it did not differ reliably between maskers. CONCLUSIONS: It is often assumed that speech perception in a speech masker places greater demands on a listener's ability to segregate and selectively attend to the target than a noise masker. This assumption is based on results showing larger child/adult differences for speech perception in a speech masker composed of a small number of talkers than in spectrally matched noise. The observation that infants experience equal masking for speech and noise maskers suggests that infants experience informational masking in both maskers and raises the possibility that the cues which make the steady noise a relatively ineffective masker for children are learned.

Development of Open-Set Word Recognition in Children: Speech-Shaped Noise and Two-Talker Speech Maskers.

OBJECTIVE: The goal of this study was to establish the developmental trajectories for children's open-set recognition of monosyllabic words in each of two maskers: two-talker speech and speech-shaped noise. DESIGN: Listeners were 56 children (5 to 16 years) and 16 adults, all with normal hearing. Thresholds for 50% correct recognition of monosyllabic words were measured in a two-talker speech or a speech-shaped noise masker in the sound field using an open-set task. Target words were presented at a fixed level of 65 dB SPL throughout testing, while the masker level was adapted. A repeated-measures design was used to compare the performance of three age groups of children (5 to 7 years, 8 to 12 years, and 13 to 16 years) and a group of adults. The pattern of age-related changes during childhood was also compared between the two masker conditions. RESULTS: Listeners in all four age groups performed more poorly in the two-talker speech than the speech-shaped noise masker, but the developmental trajectories differed for the two masker conditions. For the speech-shaped noise masker, children's performance improved with age until about 10 years of age, with little systematic child-adult differences thereafter. In contrast, for the two-talker speech masker, children's thresholds gradually improved between 5 and 13 years of age, followed by an abrupt improvement in performance to adult-like levels. Children's thresholds in the two masker conditions were uncorrelated. CONCLUSIONS: Younger children require a more advantageous signal-to-noise ratio than older children and adults to achieve 50% correct word recognition in both masker conditions. However, children's ability to recognize words appears to take longer to mature and follows a different developmental trajectory for the two-talker speech masker than the speech-shaped noise masker. These findings highlight the importance of considering both age and masker type when evaluating children's masked speech perception abilities.