Development of Basic Auditory Discrimination in Preschool Children

The effect of gender on a frequency discrimination task in children

BACKGROUND

Physiological and behavioral sex-related differences have been previously reported in the human auditory system, although data are limited to adults and are equivocal. While physiological evidence showed some advantage for females, psychophysical data tended to show greater sensitivity for males in several auditory tasks. Possible explanations for the gender effect in the auditory system include differences between the sexes in physical dimensions of the ear, brain anatomy, exposure to androgens prenatally and/or at puberty, and/or environmental factors (e.g., auditory experience). The purpose of the present study was to investigate sex-related differences in an auditory frequency discrimination task in children prior to puberty.

METHODS

A total of 24 normal-hearing children were divided into two age groups: 7- and 8-year-olds, with six girls and six boys in each age group. All children took part in a testing session that consisted of three Difference Limen for Frequency (DLF) measurements. Cognitive tests were also conducted.

RESULTS

RESULTS showed that (a) boys outperformed the girls regardless of age; (b) age effect was significant, with older children performing better than the younger ones, irrespective of gender; (c) intrameasurement variance was smaller for the older children; and (d) age, gender, and auditory working memory and capacity explained over 65% of the variance in DLF thresholds. This is the first evidence of a gender effect in the auditory system in children prior to puberty.

CONCLUSIONS

This evidence suggests that it is more likely that inherent physiological differences between the sexes influence the differential outcomes reported in the present study.

Tactile spatial acuity in childhood: effects of age and fingertip size

Tactile acuity is known to decline with age in adults, possibly as the result of receptor loss, but less is understood about how tactile acuity changes during childhood. Previous research from our laboratory has shown that fingertip size influences tactile spatial acuity in young adults: those with larger fingers tend to have poorer acuity, possibly because mechanoreceptors are more sparsely distributed in larger fingers. We hypothesized that a similar relationship would hold among children. If so, children’s tactile spatial acuity might be expected to worsen as their fingertips grow. However, concomitant CNS maturation might result in more efficient perceptual processing, counteracting the effect of fingertip growth on tactile acuity. To investigate, we conducted a cross-sectional study, testing 116 participants ranging in age from 6 to 16 years on a precision-controlled tactile grating orientation task. We measured each participant's grating orientation threshold on the dominant index finger, along with physical properties of the fingertip: surface area, volume, sweat pore spacing, and temperature. We found that, as in adults, children with larger fingertips (at a given age) had significantly poorer acuity, yet paradoxically acuity did not worsen significantly with age. We propose that finger growth during development results in a gradual decline in innervation density as receptive fields reposition to cover an expanding skin surface. At the same time, central maturation presumably enhances perceptual processing.

Explaining coherence in coherence masking protection for adults and children

Coherence masking protection (CMP) is the phenomenon in which a low-frequency target (typically a first formant) is labeled accurately in poorer signal-to-noise levels when combined with a high-frequency cosignal, rather than presented alone. An earlier study by the authors revealed greater CMP for children than adults, with more resistance to disruptions in harmonicity across spectral components [Nittrouer and Tarr (2011). Atten. Percept. Psychophys. 73, 2606-2623]. That finding was interpreted as demonstrating that children are obliged to process speech signals as broad spectral patterns, regardless of the harmonic structure of the spectral components. The current study tested three alternative, auditory explanations for the observed coherence of target + cosignal: (1) unique spectral shapes of target + cosignal support labeling, (2) periodicity of target + cosignal promotes coherence, and (3) temporal synchrony across target + cosignal reinforces temporal expectancies. Adults, eight-year-olds, and five-year-olds labeled stimuli in five conditions: F1 only and F1 + a constant cosignal (both used previously) were benchmarks for comparing thresholds for F1 + 3 new cosignals. Children again showed greater CMP than adults, but none of the three hypotheses could explain their CMP. It was again concluded that children are obliged to recognize speech signals as broad spectral patterns.

Effects of reverberation on speech recognition in stationary and modulated noise by school-aged children and young adults

OBJECTIVES

The purpose of this study was to determine how combinations of reverberation and noise, typical of environments in many elementary school classrooms, affect normal-hearing school-aged children's speech recognition in stationary and amplitude-modulated noise, and to compare their performance with that of normal-hearing young adults. In addition, the magnitude of release from masking in the modulated noise relative to that in stationary noise was compared across age groups in nonreverberant and reverberant listening conditions. Last, for all noise and reverberation combinations the degree of change in predicted performance at 70% correct was obtained for all age groups using a best-fit cubic polynomial.

DESIGN

Bamford-Kowal-Bench sentences and noise were convolved with binaural room impulse responses representing nonreverberant and reverberant environments to create test materials representative of both audiology clinics and school classroom environments. Speech recognition of 48 school-aged children and 12 adults was measured in speech-shaped and amplitude-modulated speech-shaped noise, in the following three virtual listening environments: nonreverberant, reverberant at 2 m, and reverberant at 6 m.

RESULTS

Speech recognition decreased in the reverberant conditions and with decreasing age. Release from masking in modulated noise relative to stationary noise decreased with age and was reduced by reverberation. In the nonreverberant condition, participants showed similar amounts of masking release across ages. The slopes of performance-intensity functions increased with age, with the exception of the nonreverberant modulated masker condition. The slopes were steeper in the stationary masker conditions, where they also decreased with reverberation and distance. In the presence of a modulated masker, the slopes did not differ between the two reverberant conditions.

CONCLUSIONS

The results of this study reveal systematic developmental changes in speech recognition in noisy and reverberant environments for elementary-school-aged children. The overall pattern suggests that younger children require better acoustic conditions to achieve sentence recognition equivalent to their older peers and adults. In addition, this is the first study to report a reduction of masking release in children as a result of reverberation. Results support the importance of minimizing noise and reverberation in classrooms, and highlight the need to incorporate noise and reverberation into audiological speech-recognition testing to improve predictions of performance in the real world.

A computer-based auditory sequential pattern test for school-aged children

OBJECTIVE

One type of test commonly used to assess auditory processing disorders (APD) is the Frequency Pattern Test, in which triads of pure tones of two different frequencies are presented, and participants are required to accurately report the sequence of tones, typically using a verbal response. The test is widely used clinically, but in its current format, is an under-exploited means of addressing some candidate processes, such as temporal ordering and frequency discrimination, which might be affected in APD. Here we describe a computer-based version of an auditory pattern perception test, the BirdSong Game, which was designed to be an engaging research tool for use with school-aged children.

METHODS

In this study, 128 children aged 6-10 with normal peripheral hearing were tested. The BirdSong Game application was used to administer auditory sequential pattern tests, via a touch-screen presentation and response interface. A conditioning step was included prior to testing, in order to ensure that participants were able to adequately discriminate between the test tones, and reliably describe the difference using their own vocabulary. Responses were collected either verbally or manually, by having participants press cartoon images on the touch-screen in the appropriate sequence. The data was examined for age, gender and response mode differences.

RESULTS

Findings on the auditory tests indicated a significant maturational effect across the age range studied, with no difference between response modes or gender.

CONCLUSIONS

The BirdSong Game is sensitive to maturational changes in auditory sequencing ability, and the computer-based design of the test has several advantages which make it a potentially useful clinical and research tool.

Factors affecting the processing of intensity in school-aged children

PURPOSE

Thresholds of school-aged children are elevated relative to those of adults for intensity discrimination and amplitude modulation (AM) detection. It is unclear how these findings are related or what role stimulus gating and dynamic envelope cues play in these results. Two experiments assessed the development of sensitivity to intensity increments in different stimulus contexts.

METHOD

Thresholds for detecting an increment in level were estimated for normal-hearing children (5- to 10-year-olds) and adults. Experiment 1 compared intensity discrimination for gated and continuous presentation of a 1-kHz tone, with a 65-dB-SPL standard level. Experiment 2 compared increment detection and 16-Hz AM detection introduced into a continuous 1-kHz tone, with either 35- or 75-dB-SPL standard levels.

RESULTS

Children had higher thresholds than adults overall. All listeners were more sensitive to increments in the continuous than the gated stimulus and performed better at the 75- than at the 35-dB-SPL standard level. Both effects were comparable for children and adults. There was some evidence that children's AM detection was more adultlike than increment detection.

CONCLUSION

These results imply that memory for loudness across gated intervals is not responsible for children's poor performance but that multiple dynamic envelope cues may benefit children more than adults.

Fast measurement of auditory event-related potential profiles in 2-3-year-olds

Auditory discrimination, memory, and attention-related functions were investigated in healthy 2-3-year-olds by recording event-related potentials (ERPs) to changes in five auditory features and two types of novel sounds using the fast multifeature paradigm (MFP). ERP profiles consisting of the mismatch negativity (MMN), P3a, and prominent late discriminative negativities (LDN) were obtained, for the first time, from this age group in a considerably shorter time compared to the traditional paradigms. Statistically significant responses from individual children were obtained mainly for the novel sounds. Thus, the MFP shows promise as a time-efficient paradigm for investigating central auditory functions in toddlers.

Sensitivity of school-aged children to pitch-related cues

Two experiments investigated the ability of 17 school-aged children to process purely temporal and spectro-temporal cues that signal changes in pitch. Percentage correct was measured for the discrimination of sinusoidal amplitude modulation rate (AMR) of broadband noise in experiment 1 and for the discrimination of fundamental frequency (F0) of broadband sine-phase harmonic complexes in experiment 2. The reference AMR was 100 Hz as was the reference F0. A child-friendly interface helped listeners to remain attentive to the task. Data were fitted using a maximum-likelihood technique that extracted threshold, slope, and lapse rate. All thresholds were subsequently standardized to a common d' value equal to 0.77. There were relatively large individual differences across listeners: eight had relatively adult-like thresholds in both tasks and nine had higher thresholds. However, these individual differences did not vary systematically with age, over the span of 6-16 yr. Thresholds were correlated across the two tasks and were about nine times finer for F0 discrimination than for AMR discrimination as has been previously observed in adults.

A behavioral framework to guide research on central auditory development and plasticity

The auditory CNS is influenced profoundly by sounds heard during development. Auditory deprivation and augmented sound exposure can each perturb the maturation of neural computations as well as their underlying synaptic properties. However, we have learned little about the emergence of perceptual skills in these same model systems, and especially how perception is influenced by early acoustic experience. Here, we argue that developmental studies must take greater advantage of behavioral benchmarks. We discuss quantitative measures of perceptual development and suggest how they can play a much larger role in guiding experimental design. Most importantly, including behavioral measures will allow us to establish empirical connections among environment, neural development, and perception.

Separable developmental trajectories for the abilities to detect auditory amplitude and frequency modulation

Amplitude modulation (AM) and frequency modulation (FM) are inherent components of most natural sounds. The ability to detect these modulations, considered critical for normal auditory and speech perception, improves over the course of development. However, the extent to which the development of AM and FM detection skills follow different trajectories, and therefore can be attributed to the maturation of separate processes, remains unclear. Here we explored the relationship between the developmental trajectories for the detection of sinusoidal AM and FM in a cross-sectional design employing children aged 8-10 and 11-12 years and adults. For FM of tonal carriers, both average performance (mean) and performance consistency (within-listener standard deviation) were adult-like in the 8-10 y/o. In contrast, in the same listeners, average performance for AM of wideband noise carriers was still not adult-like in the 11-12 y/o, though performance consistency was already mature in the 8-10 y/o. Among the children there were no significant correlations for either measure between the degrees of maturity for AM and FM detection. These differences in developmental trajectory between the two modulation cues and between average detection thresholds and performance consistency suggest that at least partially distinct processes may underlie the development of AM and FM detection as well as the abilities to detect modulation and to do so consistently.

Perceptual anchoring in preschool children: not adultlike, but there

BACKGROUND

Recent studies suggest that human auditory perception follows a prolonged developmental trajectory, sometimes continuing well into adolescence. Whereas both sensory and cognitive accounts have been proposed, the development of the ability to base current perceptual decisions on prior information, an ability that strongly benefits adult perception, has not been directly explored. Here we ask whether the auditory frequency discrimination of preschool children also improves when given the opportunity to use previously presented standard stimuli as perceptual anchors, and whether the magnitude of this anchoring effect undergoes developmental changes.

METHODOLOGY/PRINCIPAL FINDINGS

Frequency discrimination was tested using two adaptive same/different protocols. In one protocol (with-reference), a repeated 1-kHz standard tone was presented repeatedly across trials. In the other (no-reference), no such repetitions occurred. Verbal memory and early reading skills were also evaluated to determine if the pattern of correlations between frequency discrimination, memory and literacy is similar to that previously reported in older children and adults. Preschool children were significantly more sensitive in the with-reference than in the no-reference condition, but the magnitude of this anchoring effect was smaller than that observed in adults. The pattern of correlations among discrimination thresholds, memory and literacy replicated previous reports in older children.

CONCLUSIONS/SIGNIFICANCE

The processes allowing the use of context to form perceptual anchors are already functional among preschool children, albeit to a lesser extent than in adults. Nevertheless, immature anchoring cannot fully account for the poorer frequency discrimination abilities of young children. That anchoring is present among the majority of typically developing preschool children suggests that the anchoring deficits observed among individuals with dyslexia represent a true deficit rather than a developmental delay.

[Significance of auditory perceptual disorders for pediatric and adolescent psychiatric disorders]

The clinical relevance of central auditory processing disorders (CAPD) is highly controversial. The paper explicates different concepts of CAPD and reviews empirical studies of the relationship between auditory deficits and learning or psychiatric disorders. The overview of the available literature reveals that numerous authors have described subnormal auditory abilities in groups of children with developmental language disorders, dyslexia or ADHD. However, little or no relationship between the severity of clinical impairment and auditory deficits has been found. Thus auditory deficits do not appear to be causally related to learning disorders or conduct disorders. With respect to the diagnostic process the review makes clear that the validity of the diagnosis CAPD is low. There is no agreement about diagnostic criteria, and the reliability of most auditory tests in insufficient. Moreover, while an auditory training can only improve the directly trained auditory functions, there is no transfer effect to learning ability of behavior. Altogether there is little evidence for a significant relevance of CAPD in Child and Adolescent Psychiatry.

Psychometric functions for pure tone intensity discrimination: slope differences in school-aged children and adults

Previous work on pure tone intensity discrimination in school-aged children concluded that children might have higher levels of internal noise than adults for this task [J. Acoust. Soc. Am. 120, 2777-2788 (2006)]. If true, this would imply that psychometric function slopes are shallower for children than adults, a prediction that was tested in the present experiment. Normal hearing children (5-9 yr) and adults were tested in a two-stage protocol. The first stage used a tracking procedure to estimate 71% correct for intensity discrimination with a gated 500 Hz pure tone and a 65 dB sound pressure level standard level. The mean and standard deviation of these tracks were used to identify a set of five signal levels for each observer. In the second stage of the experiment percent correct was estimated at these five levels. Psychometric functions fitted to these data were significantly shallower for children than adults, as predicted by the internal noise hypothesis. Data from both stages of testing are consistent with a model wherein performance is based on a stable psychometric function, with sensitivity limited by psychometric function slope. Across observers the relationship between slope and threshold conformed closely to predictions of a simple signal detection model.

Frequency discrimination learning in children

Psychoacoustic thresholds of pure tone frequency discrimination (FD) in children are elevated relative to those of adults. It has been shown that it is possible to improve FD thresholds in adults, following a single (subhour) training session. To determine whether FD thresholds in children may be improved by training and, consequently, reduced to adult levels, 100 normally hearing 6- to 11-year-old children and adults received approximately 1 h of training on a FD task at 1 kHz. At the start of training, a quarter of all child participants had FD thresholds that resembled those of naive adults (adult-like subgroup). Another quarter achieved thresholds that were adult-like at some point during training (trainable subgroup). For the remainder (nonadult-like subgroup), thresholds did not reach those of naive adult listeners at any point in the training session. Subgroup membership was linked to the influence of three factors-age, nonverbal IQ, and attention. However, across subgroups, learning was found not to generalize to either a different standard frequency (4 kHz) or a variable (roving) presentation paradigm. The results indicate that it is possible for some children to achieve FD thresholds comparable to those of naive adults, either natively or after limited training.

Development of auditory selective attention: event-related potential measures of channel selection and target detection

In this study, we examined developmental changes in auditory selective attention using both electrophysiological (Nd, P3b) and behavioral measures while two groups of children (9- and 12-year-olds) and adults were engaged in a two-channel selective attention task. Channel was determined by frequency (1000 or 2000 Hz). Targets in one condition were shorter than the standards (duration target) and in the other were softer (intensity target). We found that the Nd onset and peak latencies for the children were significantly longer than for the adults. Nd amplitude, however, did not differ between the groups. Further, all groups evidenced P3b to attended targets but not to unattended deviants. Hits, reaction times, and false alarms to unattended deviants continued to evidence improvements through adolescence. Taken together, our data are most consistent with a model of developmental improvement in the speed and efficiency of attention allocation.

Children's weighting strategies for word-final stop voicing are not explained by auditory sensitivities

PURPOSE

It has been reported that children and adults weight differently the various acoustic properties of the speech signal that support phonetic decisions. This finding is generally attributed to the fact that the amount of weight assigned to various acoustic properties by adults varies across languages, and that children have not yet discovered the mature weighting strategies of their own native languages. But an alternative explanation exists: Perhaps children's auditory sensitivities for some acoustic properties of speech are poorer than those of adults, and children cannot categorize stimuli based on properties to which they are not keenly sensitive. The purpose of the current study was to test that hypothesis.

METHOD

Edited-natural, synthetic-formant, and sine wave stimuli were all used, and all were modeled after words with voiced and voiceless final stops. Adults and children (5 and 7 years of age) listened to pairs of stimuli in 5 conditions: 2 involving a temporal property (1 with speech and 1 with nonspeech stimuli) and 3 involving a spectral property (1 with speech and 2 with nonspeech stimuli). An AX discrimination task was used in which a standard stimulus (A) was compared with all other stimuli (X) equal numbers of times (method of constant stimuli).

RESULTS

Adults and children had similar difference thresholds (i.e., 50% point on the discrimination function) for 2 of the 3 sets of nonspeech stimuli (1 temporal and 1 spectral), but children's thresholds were greater for both sets of speech stimuli.

CONCLUSION

Results are interpreted as evidence that children's auditory sensitivities are adequate to support weighting strategies similar to those of adults, and so observed differences between children and adults in speech perception cannot be explained by differences in auditory perception. Furthermore, it is concluded that listeners bring expectations to the listening task about the nature of the signals they are hearing based on their experiences with those signals.

Development and the role of internal noise in detection and discrimination thresholds with narrow band stimuli

The experiments reported here examine the role of internal noise in the detection of a tone in narrow band noise and intensity discrimination for narrow band stimuli in school-aged children as compared to adults. Experiment 1 used 20-Hz wide bands of Gaussian and low-fluctuation noise centered at 500 Hz to assess the role of stimulus fluctuation in detection of a 500-Hz pure tone. Additional conditions tested whether performance was based on level and/or level-independent cues. Children's thresholds were elevated with respect to adults, and whereas adults benefited from the reduced fluctuation of low-fluctuation noise, children did not. Results from both groups were consistent with the use of a level cue. Experiment 2 estimated intensity increment thresholds for a narrow band Gaussian noise or a pure tone, either with or without a presentation-by-presentation level rove, an additional source of level variability. Stimulus variability was found to have a larger effect on performance of adults as compared to children, a rather counterintuitive finding if one thinks of children as more prone to informational masking introduced by stimulus variability. Both tone-in-noise and intensity discrimination data were consistent with the hypothesis that children's performance is limited by greater levels of internal noise.

Auditory temporal information processing in preschool children at family risk for dyslexia: relations with phonological abilities and developing literacy skills

In this project, the hypothesis of an auditory temporal processing deficit in dyslexia was tested by examining auditory processing in relation to phonological skills in two contrasting groups of five-year-old preschool children, a familial high risk and a familial low risk group. Participants were individually matched for gender, age, non-verbal IQ, school environment, and parental educational level. Psychophysical thresholds were estimated for gap-detection, frequency modulation detection, and tone-in-noise detection using a three-interval forced-choice adaptive staircase paradigm embedded within a computer game. Phonological skills were measured by tasks assessing phonological awareness, rapid serial naming, and verbal short-term memory. Significant group differences were found for phonological awareness and letter knowledge. In contrast, none of the auditory tasks differentiated significantly between both groups. However, both frequency modulation and tone-in-noise detection were significantly related to phonological awareness. This relation with phonological skills was not present for gap-detection.

Perception and production of English vowels by Mandarin speakers: age-related differences vary with amount of L2 exposure

In this study we assessed age-related differences in the perception and production of American English (AE) vowels by native Mandarin speakers as a function of the amount of exposure to the target language. Participants included three groups of native Mandarin speakers: 87 children, adolescents and young adults living in China, 77 recent arrivals who had lived in the U.S. for two years or less, and 54 past arrivals who had lived in the U.S. between three and five years. The latter two groups arrived in the U.S. between the ages of 7 and 44 years. Discrimination of six AE vowel pairs /i-i/, /i-e(I)/, /e-ae/, /ae-a/, /a-(symbol see text)/, and /u-a/ was assessed with a categorial AXB task. Production of the eight vowels /i, i, e(I), e, ae, (symbol see text), a, u/ was assessed with an immediate imitation task. Age-related differences in performance accuracy changed from an older-learner advantage among participants in China, to no age differences among recent arrivals, and to a younger-learner advantage among past arrivals. Performance on individual vowels and vowel contrasts indicated the influence of the Mandarin phonetic/phonological system. These findings support a combined environmental and L1 interference/transfer theory as an explanation of the long-term younger-learner advantage in mastering L2 phonology.

Auditory frequency discrimination in children with specific language impairment: a longitudinal study

It has been proposed that specific language impairment (SLI) is caused by an impairment of auditory processing, but it is unclear whether this problem affects temporal processing, frequency discrimination (FD), or both. Furthermore, there are few longitudinal studies in this area, making it hard to establish whether any deficit represents a developmental lag or a more permanent deficit. To address these issues, the authors retested a group of 10 children with SLI and 12 control children first tested 42 months previously. At Time 1, the children with SLI (between 9 and 12 years of age) had significantly elevated FD thresholds compared to the matched controls. At Time 2, the thresholds of both groups had improved, but the children with SLI still had poorer FD thresholds than those of the controls. To assess temporal resolution, auditory backward masking was measured and it was found that most of the children with SLI performed as well as the controls, but 2 children had exceptionally high thresholds. There was also greater variability among the children with SLI compared to that measured among the controls on the FD task. These studies indicate considerable heterogeneity in auditory function among children with SLI and suggest that, as with auditory temporal deficits, difficulties in FD discrimination are important in this population.

Are there critical periods for musical development?

A critical period can be defined as a developmental window during which specific experience has a greater effect than at other times. Musical behavior involves many skills, including the basic encoding of pitch and time information, understanding scale and harmonic structure, performance, interpretation, and composition. We review studies of genetics, behavior, and brain structure and function in conjunction with the experiences of auditory deprivation and musical enrichment, and conclude that there is more supporting evidence for critical periods for basic than for more complex aspects of musical pitch acquisition. Much remains unknown about the mechanisms of interaction between genetic and experiential factors that create critical periods, but it is clear that there are multiple pathways for achieving musical expertise.

The influence of spectral distinctiveness on acoustic cue weighting in children's and adults' speech perception

Children and adults appear to weight some acoustic cues differently in perceiving certain speech contrasts. One possible explanation for this difference is that children and adults make use of different strategies in the way that they process speech. An alternative explanation is that adult-child cue weighting differences are due to more general sensory (auditory) processing differences between the two groups. It has been proposed that children may be less able to deal with incomplete or insufficient acoustic information than are adults, and thus may require cues that are longer, louder, or more spectrally distinct to identify or discriminate between auditory stimuli. The current study tested this hypothesis by examining adults' and 3- to 7-year-old children's cue weighting for contrasts in which vowel-onset formant transitions varied from spectrally distinct (/no/-/mo/, /do/-/bo/, and /ta/-/da/) to spectrally similar (/ni/-/mi/, /de/-/be/, and /ti/-/di/). Spectrally distinct cues were more likely to yield different consonantal responses than were spectrally similar cues, for all listeners. Furthermore, as predicted by a sensory hypothesis, children were less likely to give different consonantal responses to stimuli distinguished by spectrally similar transitional cues than were adults. However, this pattern of behavior did not hold for all contrasts. Implications for theories of adult-child cue weighting differences are discussed.

Sensory and nonsensory influences on children's performance of dichotic pitch perception tasks

Dichotic pitch perception reflects the auditory system's use of binaural cues to perceptually separate different sound sources and to determine the spatial location of sounds. Several studies were conducted to identify factors that influence children's dichotic pitch perception thresholds. An initial study of school children revealed an age-related improvement in thresholds for lateralizing dichotic pitch tones. In subsequent studies potential sensory and nonsensory limitations on young children's performance of dichotic pitch lateralization tasks were examined. A training study showed that with sufficient practice, young children lateralize dichotic pitch stimuli as well as adults, indicating an age difference in perceptual learning of the lateralization task. Changing the task requirements so that young children made a judgment about the pitch of dichotic pitch tones, rather than the spatial location of the tones, also resulted in significantly better thresholds. These findings indicate that nonsensory factors limit young children's performance of dichotic pitch tasks.

Development of Auditory Temporal Resolution in School-Age Children Revealed by Word Recognition in Continuous and Interrupted Noise

OBJECTIVE

The purpose of the study was to investigate the development of one aspect of auditory temporal resolution in normal-hearing school-age children with word recognition in quiet and in spectrally identical continuous and interrupted noise. Typically, listeners experience a perceptual advantage (i.e., a "release from masking") in the interrupted noise relative to the continuous noise at equivalent signal-to-noise ratios (S/Ns). Any release from masking observed with children in the interrupted noise compared with the continuous noise at equivalent S/Ns could be interpreted as evidence for acquired temporal resolution ability. Differences in the amount of release from masking in the interrupted noise between children and adults could be interpreted as development of temporal resolution ability, or lack thereof, as revealed by word recognition in noise. It was hypothesized that word recognition performance would be poorer in children than adults; performance differences would be more pronounced with competition; word recognition performance would reach an asymptote to adult levels sooner in quiet than with competing stimuli; children would demonstrate better performance in the interrupted noise relative to the continuous noise (i.e., display a release from masking); and younger children would experience less release from masking compared with older children and adults (i.e., have less developed temporal resolution).

DESIGN

Eighty normal-hearing children aged 6 to 15 yr and 16 normal-hearing young adults participated. Word recognition performance with Northwestern University-Children's Perception of Speech (NU-CHIPs) stimuli was evaluated with an open-set response mode in quiet and in backgrounds of competing continuous steady-state and interrupted noise at S/Ns of 10, 0, -10, and -20 dB. Both noises were essentially identical in their spectral content and differed only in their temporal continuity.

RESULTS

Performance was better in the interrupted noise at poorer S/Ns, increased with increasing S/N, and improved with increasing age. Younger listeners were more susceptible to noise. They did not experience an equivalent perceptual advantage (i.e., a release from masking) in the interrupted noise at poorer S/Ns (i.e., < 10 dB) and generally required more favorable S/Ns to perform the same as the adult participants. These trends were less pronounced with increasing age. By 8 yr of age, children's performance in quiet equated that of adult levels, but it did not do so in noise until after 11 yr of age.

CONCLUSIONS

As revealed by their NU-CHIPs word recognition performance in continuous and interrupted noises, children's temporal resolving abilities improve in their early school years and reach adult performance levels after 11 yr of age. It was speculated that these changes reflect maturation in their central auditory system.

Infant discrimination of rapid auditory cues predicts later language impairment

The etiology and mechanisms of specific language impairment (SLI) in children are unknown. Differences in basic auditory processing abilities have been suggested to underlie their language deficits. Studies suggest that the neuropathology, such as atypical patterns of cerebral lateralization and cortical cellular anomalies, implicated in such impairments likely occur early in life. Such anomalies may play a part in the rapid processing deficits seen in this disorder. However, prospective, longitudinal studies in infant populations that are critical to examining these hypotheses have not been done. In the study described, performance on brief, rapidly-presented, successive auditory processing and perceptual-cognitive tasks were assessed in two groups of infants: normal control infants with no family history of language disorders and infants from families with a positive family history for language impairment. Initial assessments were obtained when infants were 6-9 months of age (M=7.5 months) and the sample was then followed through age 36 months. At the first visit, infants' processing of rapid auditory cues as well as global processing speed and memory were assessed. Significant differences in mean thresholds were seen in infants born into families with a history of SLI as compared with controls. Examination of relations between infant processing abilities and emerging language through 24 months-of-age revealed that threshold for rapid auditory processing at 7.5 months was the single best predictor of language outcome. At age 3, rapid auditory processing threshold and being male, together predicted 39-41% of the variance in language outcome. Thus, early deficits in rapid auditory processing abilities both precede and predict subsequent language delays. These findings support an essential role for basic nonlinguistic, central auditory processes, particularly rapid spectrotemporal processing, in early language development. Further, these findings provide a temporal diagnostic window during which future language impairments may be addressed.

Children's detection of pure-tone signals with random multitone maskers

Preschoolers and adults were asked to detect a 1000-Hz signal, which was masked by a multitone complex. The frequencies and amplitudes of the components in the complex varied randomly and independently on each presentation. A staircase, cued two-interval, forced-choice procedure disguised as a "listening game" was used to obtain signal thresholds in quiet and in the presence of the multitone maskers. The number of components in the masker was fixed within an experimental condition and varied from 2 to 906 across experimental conditions. Thresholds were also measured with a broadband noise masker. Eight preschool children and eight adults were tested. Although individual differences were large, among both adults and children, there was little difference between the groups in the mean amount of masking produced by the maskers with large numbers of components (400 and 906). There was also a small but significant difference between adults and children in the mean amount of masking produced by the broadband noise. The difference between the groups was much larger with smaller numbers of components. Data obtained from the adults were basically similar to that previously reported [cf. Neff and Green, Percept. Psychophys. 41, 409-415 (1987); Oh and Lutfi, J. Acoust. Soc. Am. 104, 3489-3499 (1998)]: maskers comprised of 10-40 components produced as much as 30 to 60 dB of masking in some, but not all listeners. Those same maskers produced larger amounts of masking (70-83 dB) in many of the preschool children, although, as in the adult group, individual differences were large. The component-relative-entropy (CoRE) model [Lutfi, J. Acoust. Soc. Am. 94, 748-758 (1993)] was used to describe the differences in performance between the children and adults. According to this model the average child appears to integrate information over a larger number of auditory filters than the average adult.

The relation between stimulus context, speech audibility, and perception for normal-hearing and hearing-impaired children

In this study, the influence of stimulus context and audibility on sentence recognition was assessed in 60 normal-hearing children, 23 hearing-impaired children, and 20 normal-hearing adults. Performance-intensity (PI) functions were obtained for 60 semantically correct and 60 semantically anomalous sentences. For each participant, an audibility index (AI) was calculated at each presentation level, and a logistic function was fitted to rau-transformed percent-correct values to estimate the SPL and AI required to achieve 70% performance. For both types of sentences, there was a systematic age-related shift in the PI functions, suggesting that young children require a higher AI to achieve performance equivalent to that of adults. Improvement in performance with the addition of semantic context was statistically significant only for the normal-hearing 5-year-olds and adults. Data from the hearing-impaired children showed age-related trends that were similar to those of the normal-hearing children, with the majority of individual data falling within the 5th and 95th percentile of normal. The implications of these findings in terms of hearing-aid fitting strategies for young children are discussed.

Noise increment detection in children 1 to 3 years of age

Studies using burst comparison procedures to examine age-related changes in intensity discrimination have reported that the ability to discriminate differences in intensity does not reach maturity until late childhood. In the present study, developmental changes in intensity discrimination were examined in 1- to 3-year-old children, using an increment detection paradigm. Children and adults detected increments in a continuous standard presented at three levels ranging from 35 to 55 dB SPL. Adults were also tested at lower levels of the standard in order to permit age comparisons at equivalent sensation levels. Standard stimuli were two-octave bands of noise centered at either 400 or 4000 Hz, and increments were 200 msec in duration. Discrimination performance improved significantly with both age and level of the standard. For all age groups, performance was significantly better for high- than for low-frequency stimuli, but frequency-dependent differences in increment thresholds did not vary reliably with age. Age differences were largest at low levels of the standard. At the highest level (approximately 30 dB nHL), children's difference limens for both low- and high-frequency noise bands were adultlike by 3 years of age. These results suggest that the developmental time course of increment detection is more rapid than that previously reported in burst comparison studies.

Speech-sound discrimination in school-age children: psychophysical and neurophysiologic measures

This study measured behavioral speech-sound discrimination and a neurophysiologic correlate of discrimination in normal school-age children (ages 6 to 15) to determine if developmental effects exist. Just noticeable differences (JNDs) and mismatch responses (MMNs) were assessed for synthetic syllables that differed in third-formant onset frequency (/da-ga/) and formant transition duration (/ba-wa/). These stimuli were selected because children with learning problems often find it difficult to discriminate rapid spectrotemporal changes like /da-ga/, whereas the ability to distinguish /ba-wa/ is relatively unimpaired. Results indicate that JNDs for /da-ga/ show no developmental effects and that JNDs for /ba-wa/ decrease slightly with age (although likely for task-related reasons). MMNs elicited by two /da-ga/ stimulus pairs (onset frequency differences = 20 Hz, 280 Hz) and three /ba-wa/ stimulus pairs (transition duration differences = 3, 5, 15 ms) showed no systematic or significant differences for onset latency, duration, or area as a function of age. Normative JND and MMN data are provided. These norms provide a metric against which children with suspected central auditory processing difficulties or auditory-based language disorders can be compared.

Brief-tone frequency discrimination by children

This study investigated maturational changes in children's ability to discriminate the frequency of short-duration tone pulses. Frequency difference limens (DLs) were measured for digitally generated 1000-Hz tones with pulse durations of 200, 50, and 20 ms using a two-alternative, two-interval, forced-choice procedure. Participants were 16 5-year-old children; 10 children each in the age categories of 7, 9, and 11 years; and a control group of 10 young adults. Eleven of the 5-year-old children were unable to learn the experimental task. All children in the three older groups and the adults successfully completed the study. The five 5-year-old children who completed the task performed similarly to the 7-year-old children. All groups of participants showed an inverse relationship between duration of the signal and the size of the DL. The DLs at all three tone durations were significantly larger for the 7-year-old children than they were for the older children and adults. There were no significant differences in DL size among the 9-year-old, 11-year-old, and adult subjects at any tone duration. These findings suggest that the sensory and/or cognitive skills required to discriminate the frequency of brief-duration tones may not reach maturity until after age 7 years.

Central deafness in a young child with Moyamoya disease: paternal linkage in a Caucasian family: two case reports and a review of the literature

A case of 'central deafness' is presented in a 3-year-old male Caucasian child with Moyamoya disease (MMD); a rare, progressive and occlusive cerebrovascular disorder predominantly affecting the carotid artery system. Documentation of normal peripheral auditory function and brainstem pathway integrity is provided by acoustic admittance, otoacoustic emission and brainstem auditory evoked potential measurements. The lack of behavioral response to sound, and absent middle and long latency auditory evoked potentials suggest thalamo-cortical dysfunction. Magnetic resonance imaging showed diffuse ischemic damage in subcortical white matter including areas of the temporal lobes. In addition, there were multiple and focal cortical infarctions in both cerebral hemispheres, focused primarily in the frontal, parietal and temporal areas. Taken together, these structural and functional abnormalities in addition to severely delayed speech and language development are consistent with the diagnosis of central deafness and suggest a disconnection between higher brainstem and cortical auditory areas. The child's father also has MMD, but was diagnosed only recently. The presence of paternal linkage is informative since it rules out x-linked recessive and maternal inheritance. To our knowledge, this represents the first documented case of paternal linkage in MMD with central deafness in a Caucasian child with no apparent Japanese ancestry. Herein, we focus on central auditory dysfunction and consider how lesion-induced changes have contributed to a deficit in basic auditory responsiveness, including a severe disturbance in receptive and expressive auditory-based speech and language skills.

Forward masking among infant and adult listeners

Psychophysical forward-masked thresholds were estimated for 3- and 6-month-old infants and for adults. Listeners detected a repeated 1000-Hz probe, with 16-ms rise time, no steady-state duration, and 16-ms fall time. Unmasked thresholds were determined for one group of listeners who were trained to respond when they heard the probe but not at other times. In the masking conditions, each tone burst was preceded by a 100-ms broadband noise masker at 65 dB SPL. Listeners were trained to respond when they heard the probe and masker, but not when they heard the masker alone. The masker-probe interval, delta t, was either 5, 10, 25, or 200 ms. Four groups of subjects listened in the masked conditions, each at one value of delta t. Each listener attempted to complete a block of 32 trials including four probe levels chosen to span the range of expected thresholds. "Group" thresholds, based on average psychometric functions, as well as thresholds for individual listeners, were estimated. Both group and individual thresholds declined with delta t, as expected, for both infants and adults. Infants' masked thresholds were higher than those of adults, and comparison of masked to unmasked thresholds suggested that infants demonstrate more forward masking than adults, particularly at short delta t. Forward masking appeared to have greater effects on 3-month-olds' detection than on either 6-month-olds' or adults'. Compared to adults, 6-month-olds demonstrated more forward masking only for delta t of 5 ms. Thus, susceptibility to forward masking may be nearly mature by 6 months of age.

The role of level, spectral, and temporal cues in children's detection of masked signals

Preschool-aged children and adults were asked to detect masked signals in four conditions that evaluated the role of level, spectral, and temporal cues on performance. Psychometric functions fitted to percent correct data at several signal-to-noise ratios showed higher thresholds and shallower slopes for the children in all conditions. Performance was similar in fixed and roving level conditions for both age groups suggesting use of level-invariant cues. When the signal was moved to the spectral edge of the masker the performance of the adults improved but that of the children did not. This suggested that children did not benefit from the additional cues provided by the off-center signal. Children's performance worsened when the signal was a narrow-band noise rather than a pure tone but the adults' did not, suggesting children's reliance on temporal changes in the masker with the introduction of the signal. Analyses of the stimuli suggested that the children's thresholds corresponded to signal-to-noise ratios at which multiple cues were present at magnitudes that were great enough to be discriminable.

Examining the role of auditory sensitivity in the developmental weighting shift

Studies comparing children's and adults' labeling of speech stimuli have repeatedly shown that children's phonological decisions are more strongly related to portions of the signal that involve rapid spectral change (i.e., formant transitions) and less related to other signal components than are adults' decisions. Such findings have led to a model termed the Developmental Weighting Shift, which suggests that children initially assign particularly strong weight to formant transitions to help delimit individual words in the continuous speech stream but gradually modify these strategies to be more like those of adults as they learn about word-internal structure. The goal of the current study was to test a reasonable alternative: that these apparent age-related differences in perceptual weighting strategies for speech are instead due to age-related differences in auditory sensitivity. To this end, difference limens (DLs) were obtained from children (ages 5 and 7 years) and adults for three types of acoustic properties: dynamic-spectral, static-spectral, and temporal. Two testable hypotheses were offered: Labeling results could reflect either absolute differences in sensitivity between children and adults or relative differences in sensitivity within each group. Empirical support for either hypothesis would indicate that apparent developmental changes in perceptual weighting strategies are actually due to developmental changes in auditory sensitivity to acoustic properties. Results of this study contradicted predictions of both hypotheses, sustaining the suggestion that children's perceptual weighting strategies for speech-relevant acoustic properties change as they gain experience with a native language.

Infants' detection of increments in low- and high-frequency noise

A visually reinforced operant paradigm was employed to examine the relationship between the difference limen (DL) for intensity and level of the standard during infancy. In Experiment 1, 7-month-old infants and adults detected increments in continuous noise presented via headphones at each of four levels ranging from 28 to 58 dB SPL. Noise stimuli were 2-octave bands centered at either 400 or 4000 Hz, and increments were 10 and 100 msec in duration. Infants' DLs were significantly larger than those of adult subjects and significantly larger for low- than for high-frequency stimuli. For the high-frequency noise band, infants' DLs were generally consistent with Weber's law, remaining essentially constant for standards higher than 28 dB SPL (3 dB SL) for 100-msec increments and 38 dB SPL (13 dB SL) for 10-msec increments. For low-frequency noise, infants' absolute thresholds were exceptionally high, and sensation levels of the standards were too low to adequately describe the relationship. In Experiment 2, 7-month-old infants detected 10- and 100-msec increments in 400-Hz noise stimuli presented in sound field. Infants' low-frequency DLs were large at low intensities and decreased with increases in level of the standard up to at least 30 dB SL. For both low- and high-frequency noise, the difference between DLs for 10- and 100-msec increments tended to be large at low levels of the standard and to decrease at higher levels. These results suggest that the relationship between the DL and level of the standard varies with both stimulus frequency and duration during infancy. However, stimulus-dependent immaturities in increment detection may be most evident at levels within approximately 30 dB of absolute threshold.

Binaural additivity of loudness in children and adults

Thirty-six different binaural noises were formed by crossing six right-ear intensities of a broadband noise with the same six intensities in the left ear in a 6 X 6 factorial design. Children (6-7 years of age) and adults were presented with 2 of these 36 binaural noises on a trial and asked to indicate which noise was louder. In Experiment 1, the left- and right-ear noises were in phase and differed only in intensity. In Experiment 2, the left- and right-ear noises were in opposite phase. For both the children and adults in Experiments 1 and 2, the paired comparison judgments of binaural loudness were shown to satisfy the testable axioms of conjoint measurement (transitivity and double cancellation), permitting the determination of interval scales of loudness for the left ear, right ear, and the sum of the two ears. Power functions provided a good description of the relation between loudness and sound pressure for the left and right ears of both children and adults. For both adults and children, an examination of the pattern of differences in judgments between Experiments 1 and 2 indicated that, when the noises were in phase, the contribution of the right ear to fused loudness was greater than when the noises were presented in counterphase.

A theory of neurolinguistic development

This article offers a developmental theory of language and the neural systems that lead to and subserve linguistic capabilities. Early perceptual experience and discontinuities in linguistic development suggest that language develops in four phases that occur in a fixed, interdependent sequence. In each phase of language, a unique ontogenetic function is accomplished. These functions have proprietary neural systems that vary in their degree of specialization. Of particular interest is an analytical mechanism that is responsible for linguistic grammar. This mechanism is time-locked and can only be turned on in the third phase. Confirming evidence is provided by children who are delayed in the second phase of the language learning process. These children store insufficient lexical material to activate their analytic mechanism. Inactivation behaves like damage, shifting language functions to homologous mechanisms in the nondominant hemisphere, thereby increasing functional and anatomical symmetry across the hemispheres. This atypical assembly of neurolinguistic resources produces functional but imperfect command of spoken language and may complicate learning of written language. The theory thus offers a different role for genetics and early experience, and a different interpretation of neuroanatomic findings, from those entertained in most other proposals on developmental language disorders.

Temporal resolution in infancy and subsequent language development

The MacArthur Communicative Development Inventory, a parent-report measure of vocabulary and syntax, was administered to 103 children (M = 23 months) who had participated in a study of temporal resolution when they were 6 months (n = 55) or 12 months (n = 48) of age. Children who performed above the median on the temporal resolution task in infancy were subsequently reported to have larger productive vocabularies, greater numbers of irregular word forms, and longer and more complex sentences than those who had performed below the median. Whether these findings reflect specific links between temporal resolution and language or whether they reflect general developmental factors remains to be determined.

The development of auditory behavior (or what the anatomists and physiologists have to explain)

OBJECTIVE

Infants' and children's performance in detecting and discriminating between sounds is often poorer than that of adults. Behavioral immaturity often coexists with mature-looking morphology and physiological responses from the peripheral and brain stem structures that limit performance among adults. One interpretation of this pattern of results is that "hearing" is mature but some unnamed central process is immature.

DESIGN

The approach to the problem taken here is to view auditory behavior as the process to be explained and physiological or anatomical measurements as giving us clues about the underlying processes. The development of four aspects of hearing-frequency resolution, detection, temporal resolution, and intensity resolution-is reviewed in this paper, and new data addressing these topics are presented.

RESULTS

Frequency resolution, detection, temporal resolution, and intensity resolution all undergo development during infancy and childhood, although the mechanisms underlying development vary across capacity and developmental period.

CONCLUSIONS

A coherent argument can be made that both primary auditory pathway maturation and maturation of specific central processes are involved in development. Both types of maturation continue into childhood, and both types of maturation can influence hearing directly.

Discriminability and perceptual weighting of some acoustic cues to speech perception by 3-year-olds

Studies of children's speech perception have shown that young children process speech signals differently than adults. Specifically, the relative contributions made by various acoustic parameters to some linguistic decisions seem to differ for children and adults. Such findings have led to the hypothesis that there is a developmental shift in the perceptual weighting of acoustic parameters that results from experience with a native language (i.e., the Developmental Weighting Shift). This developmental shift eventually leads the child to adopt the optimal perceptual weighting strategy for the native language being learned (i.e., one that allows the listener to make accurate decisions about the phonemic structure or his or her native language). Although this proposal has intuitive appeal, there is at least one serious challenge that can be leveled against it: Perhaps age-related differences in speech perception can appropriately be explained by age-related differences in basic auditory-processing abilities. That is, perhaps children are not as sensitive as adults to subtle differences in acoustic structure and so make linguistic decisions based on the acoustic information that is most perceptually salient. The present study tested this hypothesis for the acoustic cues relevant to fricative identity in fricative-vowel syllables. Results indicated that 3-year-olds were not as sensitive to changes in these acoustic cues as adults are, but that these age-related differences in auditory sensitivity could not entirely account for age-related differences in perceptual weighting strategies.

Developmental patterns of duration discrimination

The purpose of this study was to determine whether the auditory perceptual abilities of children are characterized by an age-related improvement in duration discrimination. Forty children, ages 4 to 10 years, and 10 adults served as subjects. Difference limens were obtained using a 350-msec broadband noise burst as the standard stimulus in a three-interval forced-choice paradigm. Data were characterized by significant differences between the performances of the 4-, 6-, and 8-year-olds and those of the adults. Acquisition of adult-like discrimination performance was demonstrated between the ages of 8 and 10 years.