Monaural temporal integration and temporally selective listening in children and adults

Effects of Self-Generated Noise on Quiet Threshold by Transducer Type in School-Age Children and Adults

Purpose Low-frequency detection thresholds in quiet vary across transducers. This experiment tested the hypothesis that transducer effects are larger in young children than adults, due to higher levels of self-generated noise in children. Method Listeners were normal-hearing 4.6- to 11.7-year-olds and adults. Warble-tone detection was measured at 125, 250, 500, and 1000 Hz with a sound-field speaker, insert earphones, and supra-aural headphones. Probe microphone recordings measured self-generated noise levels. Results Thresholds were similar across ages for speaker measurements. Transducer effects were larger for children than adults, with mean child-adult threshold differences at 125 Hz of 3.4 dB (insert earphones) and 6.6 dB (supra-aural headphones). Age effects on threshold were broadly consistent with noise levels measured in the ear canal. Conclusions Self-generated noise appears to elevate children's low-frequency thresholds measured with occluding transducers. These effects could be particularly relevant to the diagnosis of minimal and mild hearing loss in children.

The development of auditory functions

Typical development and maturation of the auditory system, at both the peripheral and central levels, is essential for the acquisition of speech, language, and auditory skills. The peripheral system generally encodes three basic parameters associated with auditory stimuli-time, frequency, and intensity. These acoustic cues are subsequently processed by the central auditory structures to reach and be perceived by the cerebral cortex. Observations of the human fetal and neonatal ear indicate that the peripheral auditory system is structurally and functionally adult-like at birth. In contrast, the central auditory system exhibits progressive anatomical and physiologic changes until early adulthood. Enriched experience with sound is fundamental and critical to auditory development. The absence of early and prolonged acoustic stimulation delays neuronal maturation, affecting the central auditory nervous system, in particular, and leading to atypical development. The present chapter reviews the various stages of development of the auditory system structures, especially the embryology of the human ear, before briefly presenting the trajectories of typical development of auditory abilities from infants to school-aged children.

Late maturation of backward masking in auditory cortex

Speech perception relies on the accurate resolution of brief, successive sounds that change rapidly over time. Deficits in the perception of such sounds, indicated by a reduced ability to detect signals during auditory backward masking, strongly relate to language processing difficulties in children. Backward masking during normal development has a longer maturational trajectory than many other auditory percepts, implicating the involvement of central auditory neural mechanisms with protracted developmental time courses. Despite the importance of this percept, its neural correlates are not well described at any developmental stage. We therefore measured auditory cortical responses to masked signals in juvenile and adult Mongolian gerbils and quantified the detection ability of individual neurons and neural populations in a manner comparable with psychoacoustic measurements. Perceptually, auditory backward masking manifests as higher thresholds for detection of a short signal followed by a masker than for the same signal in silence. Cortical masking was driven by a combination of suppressed responses to the signal and a reduced dynamic range available for signal detection in the presence of the masker. Both coding elements contributed to greater masked threshold shifts in juveniles compared with adults, but signal-evoked firing suppression was more pronounced in juveniles. Neural threshold shifts were a better match to human psychophysical threshold shifts when quantified with a longer temporal window that included the response to the delayed masker, suggesting that temporally selective listening may contribute to age-related differences in backward masking. NEW & NOTEWORTHY In children, auditory detection of backward masked signals is immature well into adolescence, and detection deficits correlate with problems in speech processing. Our auditory cortical recordings reveal immature backward masking in adolescent animals that mirrors the prolonged development seen in children. This is driven by both signal-evoked suppression and dynamic range reduction. An extended window of analysis suggests that differences in temporally focused listening may contribute to late maturing thresholds for backward masked signals.

The development of perceptual averaging: Efficiency metrics in children and adults using a multiple-observation sound-localization task

This study examined the ability of older children to integrate spatial information across sequential observations of bandpass noise. In experiment I, twelve adults and twelve 8-14 yr olds localized 1-5 sounds, all presented at the same location along a 34° speaker array. Rate of gain in response precision (as a function of N observations) was used to measure integration efficiency. Children were no worse at localizing a single sound than adults, and-unexpectedly-were no less efficient at integrating information across observations. Experiment II repeated the task using a Reverse Correlation paradigm. The number of observations was fixed (N = 5), and the location of each sound was independently randomly jittered. Relative weights were computed for each observation interval. Distance from the ideal weight-vector was used to index integration efficiency. The data showed that children were significantly less efficient integrators than adults: only reaching adult-like performance by around 11 yrs. The developmental effect was small, however, relative to the amount of individual variability, with some younger children exhibiting greater efficiency than some adults. This work indicates that sensory integration continues to mature into late childhood, but that this development is relatively gradual.

Effects of Self-Generated Noise on Estimates of Detection Threshold in Quiet for School-Age Children and Adults

OBJECTIVES

Detection thresholds in quiet become adult-like earlier in childhood for high than low frequencies. When adults listen for sounds near threshold, they tend to engage in behaviors that reduce physiologic noise (e.g., quiet breathing), which is predominantly low frequency. Children may not suppress self-generated noise to the same extent as adults, such that low-frequency self-generated noise elevates thresholds in the associated frequency regions. This possibility was evaluated by measuring noise levels in the ear canal simultaneous with adaptive threshold estimation.

DESIGN

Listeners were normal-hearing children (4.3 to 16.0 years) and adults. Detection thresholds were measured adaptively for 250-, 1000-, and 4000-Hz pure tones using a three-alternative forced-choice procedure. Recordings of noise in the ear canal were made while the listeners performed this task, with the earphone and microphone routed through a single foam insert. Levels of self-generated noise were computed in octave-wide bands. Age effects were evaluated for four groups: 4- to 6-year olds, 7- to 10-year olds, 11- to 16-year olds, and adults.

RESULTS

Consistent with previous data, the effect of child age on thresholds was robust at 250 Hz and fell off at higher frequencies; thresholds of even the youngest listeners were similar to adults' at 4000 Hz. Self-generated noise had a similar low-pass spectral shape for all age groups, although the magnitude of self-generated noise was higher in younger listeners. If self-generated noise impairs detection, then noise levels should be higher for trials associated with the wrong answer than the right answer. This association was observed for all listener groups at the 250-Hz signal frequency. For adults and older children, this association was limited to the noise band centered on the 250-Hz signal. For the two younger groups of children, this association was strongest at the signal frequency, but extended to bands spectrally remote from the 250-Hz signal. For the 1000-Hz signal frequency, there was a broadly tuned association between noise and response only for the two younger groups of children. For the 4000-Hz signal frequency, only the youngest group of children demonstrated an association between responses and noise levels, and this association was particularly pronounced for bands below the signal frequency.

CONCLUSIONS

These results provide evidence that self-generated noise plays a role in the prolonged development of low-frequency detection thresholds in quiet. Some aspects of the results are consistent with the possibility that self-generated noise elevates thresholds via energetic masking, particularly at 250 Hz. The association between behavioral responses and noise spectrally remote from the signal frequency is also consistent with the idea that self-generated noise may also reflect contributions of more central factors (e.g., inattention to the task). Evaluation of self-generated noise could improve diagnosis of minimal or mild hearing loss.

Gap Detection in School-Age Children and Adults: Center Frequency and Ramp Duration

PURPOSE

The age at which gap detection becomes adultlike differs, depending on the stimulus characteristics. The present study evaluated whether the developmental trajectory differs as a function of stimulus frequency region or duration of the onset and offset ramps bounding the gap.

METHOD

Thresholds were obtained for wideband noise (500-4500 Hz) with 4- or 40-ms raised-cosine ramps and for a 25-Hz-wide low-fluctuation narrowband noise centered on either 500 or 5000 Hz with 40-ms ramps. Stimuli were played continuously at 70 dB SPL, and the task was to indicate which of 3 intervals contained a gap. Listeners were 5.2- to 15.1-year-old children (n = 40) and adults (n = 10) with normal hearing.

RESULTS

Regardless of listener age, gap detection thresholds for the wideband noise tended to be lower when gaps were shaped using 4-ms rather than 40-ms ramps. Thresholds also tended to be lower for the low-fluctuation narrowband noise centered on 5000 Hz than 500 Hz. Performance reached adult levels after 11 years of age for all 4 stimuli. Maturation was not uniform across individuals, however; a subset of young children performed like adults, including some 5-year-olds.

CONCLUSION

For these stimuli, the developmental trajectory was similar regardless of narrowband noise center frequency or wideband noise onset and offset ramp duration.

Development of the auditory system

Auditory development involves changes in the peripheral and central nervous system along the auditory pathways, and these occur naturally, and in response to stimulation. Human development occurs along a trajectory that can last decades, and is studied using behavioral psychophysics, as well as physiologic measurements with neural imaging. The auditory system constructs a perceptual space that takes information from objects and groups, segregates sounds, and provides meaning and access to communication tools such as language. Auditory signals are processed in a series of analysis stages, from peripheral to central. Coding of information has been studied for features of sound, including frequency, intensity, loudness, and location, in quiet and in the presence of maskers. In the latter case, the ability of the auditory system to perform an analysis of the scene becomes highly relevant. While some basic abilities are well developed at birth, there is a clear prolonged maturation of auditory development well into the teenage years. Maturation involves auditory pathways. However, non-auditory changes (attention, memory, cognition) play an important role in auditory development. The ability of the auditory system to adapt in response to novel stimuli is a key feature of development throughout the nervous system, known as neural plasticity.

Gap detection in school-age children and adults: effects of inherent envelope modulation and the availability of cues across frequency

PURPOSE

The present study evaluated the effects of inherent envelope modulation and the availability of cues across frequency on behavioral gap detection with noise-band stimuli in school-age children.

METHOD

Listeners were 34 normal-hearing children (ages 5.2-15.6 years) and 12 normal-hearing adults (ages 18.5-28.8 years). Stimuli were continuous bands of noise centered on 2000 Hz, either 1000- or 25-Hz wide. In addition to Gaussian noise at these bandwidths, there were conditions using 25-Hz-wide noise bands modified to either accentuate or minimize inherent envelope modulation (staccato and low-fluctuation noise, respectively).

RESULTS

Within the 25-Hz-wide conditions, adults' gap detection thresholds were highest in the staccato, lower in the Gaussian, and lowest in the low-fluctuation noise. Similar trends were evident in children's thresholds, although inherent envelope modulation had a smaller effect on children than on adults. Whereas adults' thresholds were comparable for the 1000-Hz-wide Gaussian and 25-Hz-wide low-fluctuation stimulus, children's performance converged on adults' performance at a younger age for the 1000-Hz-wide Gaussian stimulus.

CONCLUSIONS

Results are consistent with the idea that children are less susceptible to the disruptive effects of inherent envelope modulation than adults when detecting a gap in a narrow-band noise. Further, the ability to use spectrally distributed gap detection cues appears to mature relatively early in childhood.

The monaural temporal window based on masking period pattern data in school-aged children and adults

Several lines of evidence indicate that auditory temporal resolution improves over childhood, whereas other data implicate the development of processing efficiency. The present study used the masking period pattern paradigm to examine the maturation of temporal processing in normal-hearing children (4.8 to 10.7 yrs) compared to adults. Thresholds for a brief tone were measured at 6 temporal positions relative to the period of a 5-Hz quasi-square-wave masker envelope, with a 20-dB modulation depth, as well as in 2 steady maskers. The signal was a pure tone at either 1000 or 6500 Hz, and the masker was a band of noise, either spectrally wide or narrow (21.3 and 1.4 equivalent rectangular bandwidths, respectively). Masker modulation improved thresholds more for wide than narrow bandwidths, and adults tended to receive more benefit from modulation than young children. Fits to data for the wide maskers indicated a change in window symmetry with development, reflecting relatively greater backward masking for the youngest listeners. Data for children >6.5 yrs of age appeared more adult-like for the 6500- than the 1000-Hz signal. Differences in temporal window asymmetry with listener age cannot be entirely explained as a consequence of a higher criterion for detection in children, a form of inefficiency.

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.

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.