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

Prelingually Deaf Children With Cochlear Implants Show Better Perception of Voice Cues and Speech in Competing Speech Than Postlingually Deaf Adults With Cochlear Implants

OBJECTIVES

Postlingually deaf adults with cochlear implants (CIs) have difficulties with perceiving differences in speakers' voice characteristics and benefit little from voice differences for the perception of speech in competing speech. However, not much is known yet about the perception and use of voice characteristics in prelingually deaf implanted children with CIs. Unlike CI adults, most CI children became deaf during the acquisition of language. Extensive neuroplastic changes during childhood could make CI children better at using the available acoustic cues than CI adults, or the lack of exposure to a normal acoustic speech signal could make it more difficult for them to learn which acoustic cues they should attend to. This study aimed to examine to what degree CI children can perceive voice cues and benefit from voice differences for perceiving speech in competing speech, comparing their abilities to those of normal-hearing (NH) children and CI adults.

DESIGN

CI children's voice cue discrimination (experiment 1), voice gender categorization (experiment 2), and benefit from target-masker voice differences for perceiving speech in competing speech (experiment 3) were examined in three experiments. The main focus was on the perception of mean fundamental frequency (F0) and vocal-tract length (VTL), the primary acoustic cues related to speakers' anatomy and perceived voice characteristics, such as voice gender.

RESULTS

CI children's F0 and VTL discrimination thresholds indicated lower sensitivity to differences compared with their NH-age-equivalent peers, but their mean discrimination thresholds of 5.92 semitones (st) for F0 and 4.10 st for VTL indicated higher sensitivity than postlingually deaf CI adults with mean thresholds of 9.19 st for F0 and 7.19 st for VTL. Furthermore, CI children's perceptual weighting of F0 and VTL cues for voice gender categorization closely resembled that of their NH-age-equivalent peers, in contrast with CI adults. Finally, CI children had more difficulties in perceiving speech in competing speech than their NH-age-equivalent peers, but they performed better than CI adults. Unlike CI adults, CI children showed a benefit from target-masker voice differences in F0 and VTL, similar to NH children.

CONCLUSION

Although CI children's F0 and VTL voice discrimination scores were overall lower than those of NH children, their weighting of F0 and VTL cues for voice gender categorization and their benefit from target-masker differences in F0 and VTL resembled that of NH children. Together, these results suggest that prelingually deaf implanted CI children can effectively utilize spectrotemporally degraded F0 and VTL cues for voice and speech perception, generally outperforming postlingually deaf CI adults in comparable tasks. These findings underscore the presence of F0 and VTL cues in the CI signal to a certain degree and suggest other factors contributing to the perception challenges faced by CI adults.

The role of long-term target and masker talker familiarity in children's speech-in-speech recognition

Objectives

This study investigated the influence of long-term talker familiarity on speech-in-speech recognition in school-age children, with a specific emphasis on the role of familiarity with the mother's voice as either the target or masker speech.

Design

Open-set sentence recognition was measured adaptively in a two-talker masker. Target and masker sentences were recorded by the adult mothers of the child participants. Each child heard sentences spoken by three adult female voices during testing; their own mother's voice (familiar voice) and two unfamiliar adult female voices.

Study sample

Twenty-four school age children (8-13 years) with normal hearing.

Results

When the target speech was spoken by a familiar talker (the mother), speech recognition was significantly better compared to when the target was unfamiliar. When the masker was spoken by the familiar talker, there was no difference in performance relative to the unfamiliar masker condition. Across all conditions, younger children required a more favorable signal-to-noise ratio than older children.

Conclusion

Implicit long-term familiarity with a talker consistently improves children's speech-in-speech recognition across the age range tested, specifically when the target talker is familiar. However, performance remains unaffected by masker talker familiarity. Additionally, while target familiarity is advantageous, it does not entirely eliminate children's increased susceptibility to competing speech.

Developmental Effects in the "Vocale Rapide dans le Bruit" Speech-in-Noise Identification Test: Reference Performances of Normal-Hearing Children and Adolescents

PURPOSE

The main objective of this study was to assess the existence of developmental effects on the performance of the Vocale Rapide dans le Bruit (VRB) speech-in-noise (SIN) identification test that was recently developed for the French language and to collect reference scores for children and adolescents.

METHOD

Seventy-two native French speakers, aged 10-20 years, participated in the study. Each participant listened and repeated four lists of eight sentences, each containing three key words to be scored. The sentences were presented in free field at different signal-to-noise ratios (SNRs) using a four-talker babble noise. The SNR yielding 50% of correct repetitions of key words (SNR50) was recorded for each list.

RESULTS

A strong relationship between age and SNR50 was found, better performance occurring with increasing age (average drop in SNR50 per year: 0.34 dB). Large differences (Cohen's d ≥ 1.2) were observed between the SNR50 achieved by 10- to 13-year-old participants and those of adults. For participants aged 14-15 years, the difference fell just above the 5% level of significance. No effects of hearing thresholds or level of education were observed.

CONCLUSIONS

The study confirms the existence of developmental effects on SIN identification performance as measured using the VRB test and provides reference data for taking into account these effects during clinical practice. Explanations as to why age effects perdure during adolescence are discussed.

Development of amplitude modulation, voice onset time, and consonant identification in noise and reverberation

Children's speech understanding is vulnerable to indoor noise and reverberation: e.g., from classrooms. It is unknown how they develop the ability to use temporal acoustic cues, specifically amplitude modulation (AM) and voice onset time (VOT), which are important for perceiving distorted speech. Through three experiments, we investigated the typical development of AM depth detection in vowels (experiment I), categorical perception of VOT (experiment II), and consonant identification (experiment III) in quiet and in speech-shaped noise (SSN) and mild reverberation in 6- to 14-year-old children. Our findings suggested that AM depth detection using a naturally produced vowel at the rate of the fundamental frequency was particularly difficult for children and with acoustic distortions. While the VOT cue salience was monotonically attenuated with increasing signal-to-noise ratio of SSN, its utility for consonant discrimination was completely removed even under mild reverberation. The reverberant energy decay in distorting critical temporal cues provided further evidence that may explain the error patterns observed in consonant identification. By 11-14 years of age, children approached adult-like performance in consonant discrimination and identification under adverse acoustics, emphasizing the need for good acoustics for younger children as they develop auditory skills to process distorted speech in everyday listening environments.

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.

Perception of voice cues in school-age children with hearing aids

The just-noticeable differences (JNDs) of the voice cues of voice pitch (F0) and vocal-tract length (VTL) were measured in school-aged children with bilateral hearing aids and children and adults with normal hearing. The JNDs were larger for hearing-aided than normal-hearing children up to the age of 12 for F0 and into adulthood for all ages for VTL. Age was a significant factor for both groups for F0 JNDs, but only for the hearing-aided group for VTL JNDs. Age of maturation was later for F0 than VTL. Individual JNDs of the two groups largely overlapped for F0, but little for VTL. Hearing thresholds (unaided or aided, 500-400 Hz, overlapping with mid-range speech frequencies) did not correlate with the JNDs. However, extended low-frequency hearing thresholds (unaided, 125-250 Hz, overlapping with voice F0 ranges) correlated with the F0 JNDs. Hence, age and hearing status differentially interact with F0 and VTL perception, and VTL perception seems challenging for hearing-aided children. On the other hand, even children with profound hearing loss could do the task, indicating a hearing aid benefit for voice perception. Given the significant age effect and that for F0 the hearing-aided children seem to be catching up with age-typical development, voice cue perception may continue developing in hearing-aided children.

Can Playing a Game Improve Children's Speech Recognition? A Preliminary Study of Implicit Talker Familiarity Effects

PURPOSE

The goal was to evaluate whether implicit talker familiarization via an interactive computer game, designed for this study, could improve children's word recognition in classroom noise. It was hypothesized that, regardless of age, children would perform better when recognizing words spoken by the talker who was heard during the game they played.

METHOD

Using a one-group pretest-posttest experimental design, this study examined the impact of short-term implicit voice exposure on children's word recognition in classroom noise. Implicit voice familiarization occurred via an interactive computer game, played at home for 10 min a day for 5 days. In the game, children (8-12 years) heard one voice, intended to become the "familiar talker." Pre- and postfamiliarization, children identified words in prerecorded classroom noise. Four conditions were tested to evaluate talker familiarity and generalization effects.

RESULTS

Results demonstrated an 11% improvement when recognizing words spoken by the voice heard in the game ("familiar talker"). This was observed only for words that were heard in the game and did not generalize to unfamiliarized words. Before familiarization, younger children had poorer recognition than older children in all conditions; however, after familiarization, there was no effect of age on performance for familiarized stimuli.

CONCLUSIONS

Implicit short-term exposure to a talker has the potential to improve children's speech recognition. Therefore, leveraging talker familiarity through gameplay shows promise as a viable method for improving children's speech-in-noise recognition. However, given that improvements did not generalize to unfamiliarized words, careful consideration of exposure stimuli is necessary to optimize this approach.

The effect of stimulus type and testing method on talker discrimination of school-age children

Efficient talker discrimination (TD) improves speech understanding under multi-talker conditions. So far, TD of children has been assessed using various testing parameters, making it difficult to draw comparative conclusions. This study explored the effects of the stimulus type and variability on children's TD. Thirty-two children (7-10 years old) underwent eight TD assessments with fundamental frequency + formant changes using an adaptive procedure. Stimuli included consonant-vowel-consonant words or three-word sentences and were either fixed by run or by trial (changing throughout the run). Cognitive skills were also assessed. Thirty-one adults (18-35 years old) served as controls. The results showed (1) poorer TD for the fixed-by-trial than the fixed-by-run method, with both stimulus types for the adults but only with the words for the children; (2) poorer TD for the words than the sentences with the fixed-by-trial method only for the children; and (3) significant correlations between the children's age and TD. These results support a developmental trajectory in the use of perceptual anchoring for TD and in its reliance on comprehensive acoustic and linguistic information. The finding that the testing parameters may influence the top-down and bottom-up processing for TD should be considered when comparing data across studies or when planning new TD experiments.

Effects of Target and Masker Fundamental Frequency Contour Depth on School-Age Children's Speech Recognition in a Two-Talker Masker

PURPOSE

Maturation of the ability to recognize target speech in the presence of a two-talker speech masker extends into early adolescence. This study evaluated whether children benefit from differences in fundamental frequency (f _o) contour depth between the target and masker speech, a cue that has been shown to improve recognition in adults.

METHOD

Speech stimuli were recorded from talkers using three speaking styles, with f _o contour depths that were Flat, Normal, or Exaggerated. Targets were open-set, declarative sentences produced by a female talker, and maskers were two streams of concatenated sentences produced by a second female talker. Listeners were children (ages 5-17 years) and adults (ages 18-24 years) with normal hearing. Each listener was tested in one of the three masker styles paired with all three target styles. Speech recognition thresholds (SRTs) corresponding to 50% correct were estimated by fitting psychometric functions to adaptive track data.

RESULTS

For adults, performance did not differ significantly across conditions with matched speaking styles. A mismatch benefit was observed when combining Flat targets with the Exaggerated masker and Exaggerated targets with the Flat masker, and for both Flat and Exaggerated targets paired with the Normal masker. For children, there was a significant effect of age in all conditions. Flat targets in the Flat masker were associated with lower SRTs than the other two matched conditions, and a mismatch benefit was observed for young children only when the target f _o contour was less variable than the masker f _o contour.

CONCLUSIONS

Whereas child-directed speech often has exaggerated pitch contours, young children were better able to recognize speech with less variable f _o. Age effects were observed in the benefit of mismatched speaking styles for some conditions, which could be related to differences in baseline SRTs rather than differences in segregation abilities.

Maturation of Speech-in-Speech Recognition for Whispered and Voiced Speech

PURPOSE

Some speech recognition data suggest that children rely less on voice pitch and harmonicity to support auditory scene analysis than adults. Two experiments evaluated development of speech-in-speech recognition using voiced speech and whispered speech, which lacks the harmonic structure of voiced speech.

METHOD

Listeners were 5- to 7-year-olds and adults with normal hearing. Targets were monosyllabic words organized into three-word sets that differ in vowel content. Maskers were two-talker or one-talker streams of speech. Targets and maskers were recorded by different female talkers in both voiced and whispered speaking styles. For each masker, speech reception thresholds (SRTs) were measured in all four combinations of target and masker speech, including matched and mismatched speaking styles for the target and masker.

RESULTS

Children performed more poorly than adults overall. For the two-talker masker, this age effect was smaller for the whispered target and masker than for the other three conditions. Children's SRTs in this condition were predominantly positive, suggesting that they may have relied on a wholistic listening strategy rather than segregating the target from the masker. For the one-talker masker, age effects were consistent across the four conditions. Reduced informational masking for the one-talker masker could be responsible for differences in age effects for the two maskers. A benefit of mismatching the target and masker speaking style was observed for both target styles in the two-talker masker and for the voiced targets in the one-talker masker.

CONCLUSIONS

These results provide no compelling evidence that young school-age children and adults are differentially sensitive to the cues present in voiced and whispered speech. Both groups benefit from mismatches in speaking style under some conditions. These benefits could be due to a combination of reduced perceptual similarity, harmonic cancelation, and differences in energetic masking.

Who is Right? A Word-Identification-in-Noise Test for Young Children Using Minimal Pair Distracters

PURPOSE

Many children have difficulties understanding speech. At present, there are few assessments that test for subtle impairments in speech perception with normative data from U.K. children. We present a new test that evaluates children's ability to identify target words in background noise by choosing between minimal pair alternatives that differ by a single articulatory phonetic feature. This task (a) is tailored to testing young children, but also readily applicable to adults; (b) has minimal memory demands; (c) adapts to the child's ability; and (d) does not require reading or verbal output.

METHOD

We tested 155 children and young adults aged from 5 to 25 years on this new test of single word perception.

RESULTS

Speech-in-noise abilities in this particular task develop rapidly through childhood until they reach maturity at around 9 years of age.

CONCLUSIONS

We make this test freely available and provide associated normative data. We hope that it will be useful to researchers and clinicians in the assessment of speech perception abilities in children who are hard of hearing or have developmental language disorder, dyslexia, or auditory processing disorder.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.17155934.

Effect of Masker Head Orientation, Listener Age, and Extended High-Frequency Sensitivity on Speech Recognition in Spatially Separated Speech

OBJECTIVES

Masked speech recognition is typically assessed as though the target and background talkers are all directly facing the listener. However, background speech in natural environments is often produced by talkers facing other directions, and talker head orientation affects the spectral content of speech, particularly at the extended high frequencies (EHFs; >8 kHz). This study investigated the effect of masker head orientation and listeners' EHF sensitivity on speech-in-speech recognition and spatial release from masking in children and adults.

DESIGN

Participants were 5- to 7-year-olds (n = 15) and adults (n = 34), all with normal hearing up to 8 kHz and a range of EHF hearing thresholds. Speech reception thresholds (SRTs) were measured for target sentences recorded from a microphone directly in front of the talker's mouth and presented from a loudspeaker directly in front of the listener, simulating a target directly in front of and facing the listener. The maskers were two streams of concatenated words recorded from a microphone located at either 0° or 60° azimuth, simulating masker talkers facing the listener or facing away from the listener, respectively. Maskers were presented in one of three spatial conditions: co-located with the target, symmetrically separated on either side of the target (+54° and -54° on the horizontal plane), or asymmetrically separated to the right of the target (both +54° on the horizontal plane).

RESULTS

Performance was poorer for the facing than for the nonfacing masker head orientation. This benefit of the nonfacing masker head orientation, or head orientation release from masking (HORM), was largest under the co-located condition, but it was also observed for the symmetric and asymmetric masker spatial separation conditions. SRTs were positively correlated with the mean 16-kHz threshold across ears in adults for the nonfacing conditions but not for the facing masker conditions. In adults with normal EHF thresholds, the HORM was comparable in magnitude to the benefit of a symmetric spatial separation of the target and maskers. Although children benefited from the nonfacing masker head orientation, their HORM was reduced compared to adults with normal EHF thresholds. Spatial release from masking was comparable across age groups for symmetric masker placement, but it was larger in adults than children for the asymmetric masker.

CONCLUSIONS

Masker head orientation affects speech-in-speech recognition in children and adults, particularly those with normal EHF thresholds. This is important because masker talkers do not all face the listener under most natural listening conditions, and assuming a midline orientation would tend to overestimate the effect of spatial separation. The benefits associated with EHF audibility for speech-in-speech recognition may warrant clinical evaluation of thresholds above 8 kHz.

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.

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.

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.

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.

Extended high-frequency hearing and head orientation cues benefit children during speech-in-speech recognition

While the audible frequency range for humans spans approximately 20 Hz to 20 kHz, children display enhanced sensitivity relative to adults when detecting extended high frequencies (frequencies above 8 kHz; EHFs), as indicated by better pure tone thresholds. The impact that this increased hearing sensitivity to EHFs may have on children's speech recognition has not been established. One context in which EHF hearing may be particularly important for children is when recognizing speech in the presence of competing talkers. In the present study, we examined the extent to which school-age children (ages 5-17 years) with normal hearing were able to benefit from EHF cues when recognizing sentences in a two-talker speech masker. Two filtering conditions were tested: all stimuli were either full band or were low-pass filtered at 8 kHz to remove EHFs. Given that EHF energy emission in speech is highly dependent on head orientation of the talker (i.e., radiation becomes more directional with increasing frequency), two masker head angle conditions were tested: both co-located maskers were facing 45°, or both were facing 60° relative to the listener. The results demonstrated that regardless of age, children performed better when EHFs were present. In addition, a small change in masker head orientation also impacted performance, with better recognition at 60° compared to 45°. These findings suggest that EHF energy in the speech signal above 8 kHz is beneficial for children in complex listening situations. The magnitude of benefit from EHF cues and talker head orientation cues did not differ between children and adults. Therefore, while EHFs were beneficial for children as young as 5 years of age, children's generally better EHF hearing relative to adults did not provide any additional benefit.

Independent and Combined Effects of Fundamental Frequency and Vocal Tract Length Differences for School-Age Children's Sentence Recognition in a Two-Talker Masker

Purpose The purpose of this study was to examine the independent and combined contributions of fundamental frequency (F0) and vocal tract length (VTL) differences on children's speech-in-speech recognition in the presence of a competing two-talker masker. Method Participants were 64 children (5-17 years old) and 25 adults (18-39 years old). Sentence recognition thresholds were measured in a two-talker masker. Target sentences had either the same mean F0 and VTL of the masker or were digitally altered so that the target and masker differed in F0 (Experiment 1), differed in VTL (Experiment 2), or differed in both F0 and VTL (Experiment 3). To determine the benefit, masking release was computed by subtracting thresholds in each shifted condition from the threshold in the unshifted condition. Results Results demonstrate that children's ability to benefit from either F0 or VTL differences (Experiments 1 and 2) depended on listener age, with younger children showing less improvement in speech reception thresholds compared to older children and adults. Age effects were also evident in the combined-cue conditions (Experiment 3), but children showed greater improvements compared to F0-only or VTL-only manipulations. Conclusions There was a prolonged pattern of development in children's ability to benefit from F0 or VTL differences between target and masker speech. Young children failed to capitalize on F0 and VTL differences to the same extent as older children and adults but did show a robust benefit when the cues were combined, supporting the hypothesis that younger children rely more heavily on redundant cues compared to older children and adults.

The Clear-Speech Benefit for School-Age Children: Speech-in-Noise and Speech-in-Speech Recognition

Purpose Talkers often modify their speech when communicating with individuals who struggle to understand speech, such as listeners with hearing loss. This study evaluated the benefit of clear speech in school-age children and adults with normal hearing for speech-in-noise and speech-in-speech recognition. Method Masked sentence recognition thresholds were estimated for school-age children and adults using an adaptive procedure. In Experiment 1, the target and masker were summed and presented over a loudspeaker located directly in front of the listener. The masker was either speech-shaped noise or two-talker speech, and target sentences were produced using a clear or conversational speaking style. In Experiment 2, stimuli were presented over headphones. The two-talker speech masker was diotic (M₀). Clear and conversational target sentences were presented either in-phase (T₀) or out-of-phase (T_π) between the two ears. The M₀T_π condition introduces a segregation cue that was expected to improve performance. Results For speech presented over a single loudspeaker (Experiment 1), the clear-speech benefit was independent of age for the noise masker, but it increased with age for the two-talker masker. Similar age effects for the two-talker speech masker were seen under headphones with diotic presentation (M₀T₀), but comparable clear-speech benefit as a function of age was observed with a binaural cue to facilitate segregation (M₀T_π). Conclusions Consistent with prior research, children showed a robust clear-speech benefit for speech-in-noise recognition. Immaturity in the ability to segregate target from masker speech may limit young children's ability to benefit from clear-speech modifications for speech-in-speech recognition under some conditions. When provided with a cue that facilitates segregation, children as young as 4-7 years of age derived a clear-speech benefit in a two-talker masker that was similar to the benefit experienced by adults.

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.

Effects of Monaural Asymmetry and Target-Masker Similarity on Binaural Advantage in Children and Adults With Normal Hearing

Purpose For colocated targets and maskers, binaural listening typically offers a small but significant advantage over monaural listening. This study investigated how monaural asymmetry and target-masker similarity may limit binaural advantage in adults and children. Method Ten Mandarin-speaking Chinese adults (aged 22-27 years) and 12 children (aged 7-14 years) with normal hearing participated in the study. Monaural and binaural speech recognition thresholds (SRTs) were adaptively measured for colocated competing speech. The target-masker sex was the same or different. Performance was measured using headphones for three listening conditions: left ear, right ear, and both ears. Binaural advantage was calculated relative to the poorer or better ear. Results Mean SRTs were significantly lower for adults than children. When the target-masker sex was the same, SRTs were significantly lower with the better ear than with the poorer ear or both ears (p < .05). When the target-masker sex was different, SRTs were significantly lower with the better ear or both ears than with the poorer ear (p < .05). Children and adults similarly benefitted from target-masker sex differences. Substantial monaural asymmetry was observed, but the effects of asymmetry on binaural advantage were similar between adults and children. Monaural asymmetry was significantly correlated with binaural advantage relative to the poorer ear (p = .004), but not to the better ear (p = .056). Conclusions Binaural listening may offer little advantage (or even a disadvantage) over monaural listening with the better ear, especially when competing talkers have similar vocal characteristics. Monaural asymmetry appears to limit binaural advantage in listeners with normal hearing, similar to observations in listeners with hearing impairment. While language development may limit perception of competing speech, it does not appear to limit the effects of monaural asymmetry or target-masker sex on binaural advantage.

Infants' use of isolated and combined temporal cues in speech sound segregation

This paper investigates infants' and adults' use of envelope cues and combined onset asynchrony and envelope cues in the segregation of concurrent vowels. Listeners heard superimposed vowel pairs consisting of two different vowels spoken by a male and a female talker and were trained to respond to one specific target vowel, either the male /u:/ or male /i:/. Vowel detection was measured in three conditions. In the baseline condition the two superimposed vowels had similar amplitude envelopes and synchronous onset. In the envelope cue condition, the amplitude envelopes of the two vowels differed. In the combined cue condition, both the onset time and amplitude envelopes of the two vowels differed. Seven-month-old infants' concurrent vowel segregation improved both with envelope and with combined onset asynchrony and envelope cues to the same extent as adults'. A preliminary investigation with 3-month-old infants suggested that neither envelope cues nor combined asynchrony and envelope cues improved their ability to detect the target vowel. Taken together, these results suggest that envelope and combined onset-asynchrony cues are available to infants as they attempt to process competing speech sounds, at least after 7 months of age.

Development of voice perception is dissociated across gender cues in school-age children

Children's ability to distinguish speakers' voices continues to develop throughout childhood, yet it remains unclear how children's sensitivity to voice cues, such as differences in speakers' gender, develops over time. This so-called voice gender is primarily characterized by speakers' mean fundamental frequency (F0), related to glottal pulse rate, and vocal-tract length (VTL), related to speakers' size. Here we show that children's acquisition of adult-like performance for discrimination, a lower-order perceptual task, and categorization, a higher-order cognitive task, differs across voice gender cues. Children's discrimination was adult-like around the age of 8 for VTL but still differed from adults at the age of 12 for F0. Children's perceptual weight attributed to F0 for gender categorization was adult-like around the age of 6 but around the age of 10 for VTL. Children's discrimination and weighting of F0 and VTL were only correlated for 4- to 6-year-olds. Hence, children's development of discrimination and weighting of voice gender cues are dissociated, i.e., adult-like performance for F0 and VTL is acquired at different rates and does not seem to be closely related. The different developmental patterns for auditory discrimination and categorization highlight the complexity of the relationship between perceptual and cognitive mechanisms of voice perception.

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.

Masked Speech Recognition in School-Age Children

Children who are typically developing often struggle to hear and understand speech in the presence of competing background sounds, particularly when the background sounds are also speech. For example, in many cases, young school-age children require an additional 5- to 10-dB signal-to-noise ratio relative to adults to achieve the same word or sentence recognition performance in the presence of two streams of competing speech. Moreover, adult-like performance is not observed until adolescence. Despite ample converging evidence that children are more susceptible to auditory masking than adults, the field lacks a comprehensive model that accounts for the development of masked speech recognition. This review provides a synthesis of the literature on the typical development of masked speech recognition. Age-related changes in the ability to recognize phonemes, words, or sentences in the presence of competing background sounds will be discussed by considering (1) how masking sounds influence the sensory encoding of target speech; (2) differences in the time course of development for speech-in-noise versus speech-in-speech recognition; and (3) the central auditory and cognitive processes required to separate and attend to target speech when multiple people are speaking at the same time.

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.

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.