Loud Music Exposure and Cochlear Synaptopathy in Young Adults: Isolated Auditory Brainstem Response Effects but No Perceptual Consequences.

The purpose of this study was to test the hypothesis that listeners with frequent exposure to loud music exhibit deficits in suprathreshold auditory performance consistent with cochlear synaptopathy. Young adults with normal audiograms were recruited who either did ( n = 31) or did not ( n = 30) have a history of frequent attendance at loud music venues where the typical sound levels could be expected to result in temporary threshold shifts. A test battery was administered that comprised three sets of procedures: (a) electrophysiological tests including distortion product otoacoustic emissions, auditory brainstem responses, envelope following responses, and the acoustic change complex evoked by an interaural phase inversion; (b) psychoacoustic tests including temporal modulation detection, spectral modulation detection, and sensitivity to interaural phase; and (c) speech tests including filtered phoneme recognition and speech-in-noise recognition. The results demonstrated that a history of loud music exposure can lead to a profile of peripheral auditory function that is consistent with an interpretation of cochlear synaptopathy in humans, namely, modestly abnormal auditory brainstem response Wave I/Wave V ratios in the presence of normal distortion product otoacoustic emissions and normal audiometric thresholds. However, there were no other electrophysiological, psychophysical, or speech perception effects. The absence of any behavioral effects in suprathreshold sound processing indicated that, even if cochlear synaptopathy is a valid pathophysiological condition in humans, its perceptual sequelae are either too diffuse or too inconsequential to permit a simple differential diagnosis of hidden 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.

Effect of response context and masker type on word recognition in school-age children and adults.

In adults, masked speech recognition improves with the provision of a closed set of response alternatives. The present study evaluated whether school-age children (5-13 years) benefit to the same extent as adults from a forced-choice context, and whether this effect depends on masker type. Experiment 1 compared masked speech reception thresholds for disyllabic words in either an open-set or a four-alternative forced-choice (4AFC) task. Maskers were speech-shaped noise or two-talker speech. Experiment 2 compared masked speech reception thresholds for monosyllabic words in two 4AFC tasks, one in which the target and foils were phonetically similar and one in which they were dissimilar. Maskers were speech-shaped noise, amplitude-modulated noise, or two-talker speech. For both experiments, it was predicted that children would not benefit from the information provided by the 4AFC context to the same degree as adults, particularly when the masker was complex (two-talker) or when audible speech cues were temporally sparse (modulated-noise). Results indicate that young children do benefit from a 4AFC context to the same extent as adults in speech-shaped noise and amplitude-modulated noise, but the benefit of context increases with listener age for the two-talker speech masker.

Cochlear hearing loss and the detection of sinusoidal versus random amplitude modulation.

This study assessed the effect of cochlear hearing loss on detection of random and sinusoidal amplitude modulation. Listeners with hearing loss and normal-hearing listeners (eight per group) generated temporal modulation transfer functions (TMTFs) for envelope fluctuations carried by a 2000-Hz pure tone. TMTFs for the two groups were similar at low modulation rates but diverged at higher rates presumably because of differences in frequency selectivity. For both groups, detection of random modulation was poorer than for sinusoidal modulation at lower rates but the reverse occurred at higher rates. No evidence was found that cochlear hearing loss, per se, affects modulation detection.

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.

Factors affecting the development of speech recognition in steady and modulated noise.

This study used a checkerboard-masking paradigm to investigate the development of the speech reception threshold (SRT) for monosyllabic words in synchronously and asynchronously modulated noise. In asynchronous modulation, masker frequencies below 1300 Hz were gated off when frequencies above 1300 Hz were gated on, and vice versa. The goals of the study were to examine development of the ability to use asynchronous spectro-temporal cues for speech recognition and to assess factors related to speech frequency region and audible speech bandwidth. A speech-shaped noise masker was steady or was modulated synchronously or asynchronously across frequency. Target words were presented to 5-7 year old children or to adults. Overall, children showed higher SRTs and smaller masking release than adults. Consideration of the present results along with previous findings supports the idea that children can have particularly poor masked SRTs when the speech and masker spectra differ substantially, and that this may arise due to children requiring a wider speech bandwidth than adults for speech recognition. The results were also consistent with the idea that children are relatively poor in integrating speech cues when the frequency regions with the best signal-to-noise ratios vary across frequency as a function of time.

The Effects of Sensorineural Hearing Impairment on Asynchronous Glimpsing of Speech.

In a previous study with normal-hearing listeners, we evaluated consonant identification masked by two or more spectrally contiguous bands of noise, with asynchronous square-wave modulation applied to neighboring bands. Speech recognition thresholds were 5.1-8.5 dB better when neighboring bands were presented to different ears (dichotic) than when all bands were presented to one ear (monaural), depending on the spectral width of the frequency bands. This dichotic advantage was interpreted as reflecting masking release from peripheral spread of masking from neighboring frequency bands. The present study evaluated this effect in listeners with sensorineural hearing loss, a population more susceptible to spread of masking. Speech perception (vowel-consonant-vowel stimuli, as in /aBa/) was measured in the presence of fluctuating noise that was either modulated synchronously across frequency or asynchronously. Hearing-impaired listeners (n = 9) and normal-hearing controls were tested at either the same intensity (n = 7) or same sensation level (n = 8). Hearing-impaired listeners had mild-to-moderate hearing loss and symmetrical, flat audiometric thresholds. While all groups of listeners performed better in the dichotic than monaural condition, this effect was smaller for the hearing-impaired (3.5 dB) and equivalent-sensation-level controls (3.3 dB) than controls tested at the same intensity (11.0 dB). The present study is consistent with the idea that dichotic presentation can improve speech-in-noise listening for hearing-impaired listeners, and may be enhanced when combined with amplification.

The effect of noise fluctuation and spectral bandwidth on gap detection.

Experiment 1 investigated gap detection for random and low-fluctuation noise (LFN) markers as a function of bandwidth (25-1600 Hz), level [40 or 75 dB sound pressure level (SPL)], and center frequency (500-4000 Hz). Gap thresholds for random noise improved as bandwidth increased from 25 to 1600 Hz, but there were only minor effects related to center frequency and level. For narrow bandwidths, thresholds were lower for LFN than random markers; this difference extended to higher bandwidths at the higher center frequencies and was particularly large at high stimulus level. Effects of frequency and level were broadly consistent with the idea that peripheral filtering can increase fluctuation in the encoded LFN stimulus. Experiment 2 tested gap detection for 200-Hz-wide noise bands centered on 2000 Hz, using high-pass maskers to examine spread of excitation effects. Such effects were absent or minor for random noise markers and the 40-dB-SPL LFN markers. In contrast, some high-pass maskers substantially worsened performance for the 75-dB-SPL LFN markers. These results were consistent with an interpretation that relatively acute gap detection for the high-level LFN gap markers resulted from spread of excitation to higher-frequency auditory filters where the magnitude and phase characteristics of the LFN stimuli are better preserved.

Temporal Processing Deficits in Middle Age.

PURPOSE: The purpose of this brief report is to provide a synopsis of recent work, primarily from the authors' laboratory, that points to the emergence of temporal processing deficits relatively early in the aging process. METHOD: The approach taken was to provide a descriptive summary of selected published and current experiments focusing on the processing of temporal envelopes and fine structure. CONCLUSION: Deficits in both temporal envelope and temporal fine structure processing are evident during middle age even while audiometric hearing sensitivity remains normal.

Effect of stimulus bandwidth and duration on monaural envelope correlation perception.

Monaural envelope correlation perception is the ability to discriminate between stimuli composed of two or more bands of noise based on envelope correlation. Sensitivity decreases as stimulus bandwidth is reduced below 100 Hz. The present study manipulated stimulus bandwidth (25-100 Hz) and duration (25-800 ms) to evaluate whether performance of highly trained listeners is limited by the number of inherent modulation periods in each presentation. Stimuli were two bands of noise, separated by a 500-Hz gap centered on 2250 Hz. Performance improved reliably with increasing numbers of envelope modulation periods, although there were substantial individual differences.

Masked sentence recognition assessed at ascending target-to-masker ratios: modest effects of repeating stimuli.

OBJECTIVES: Masked sentence recognition is typically evaluated by presenting a novel stimulus on each trial. As a consequence, experiments calling for replicate estimates in multiple conditions require large corpora of stimuli. The present study evaluated the consequences of repeating sentence-plus-masker pairs at ascending target-to-masker ratios (TMRs). The hypothesis was that performance on each trial would be consistent with the cues available to the listener at the associated TMR, resulting in similar estimates of threshold and slope for procedures using novel versus repeated sentences within an ascending-TMR block of trials. DESIGN: A group of 37 normal-hearing young adults participated. Each listener was tested in the presence of one of three maskers: a multitalker babble, a speech-shaped noise, or an amplitude-modulated speech-shaped noise. There were two data collection procedures, both proceeding in blocks of trials with ascending TMRs. The novel-stimulus procedure used five lists of AzBio sentences, one presented at each of five TMRs, with a novel sentence and masker sample on each trial. The repeated-stimulus procedure used a single list of AzBio sentences, with each sentence presented at multiple TMRs, progressing from low to high; each sentence was paired with a single masker sample, such that only the TMR changed within blocks of repeated stimuli. Listeners completed one run with the novel-stimulus procedure and five runs with the repeated-stimulus procedure. The resulting values of percent correct at each TMR were fitted with a logit function to estimate threshold and psychometric function slope. RESULTS: The novel- and repeated-stimulus procedures resulted in generally similar data patterns. After controlling for effects related to the order in which listeners completed the six data collection runs, mean thresholds were slightly higher (<0.5 dB) for the repeated-stimulus procedure than the novel-stimulus procedure in all three maskers. Function slopes for the multitalker babble and amplitude-modulated noise maskers were slightly shallower using the repeated-stimulus than the novel-stimulus procedure, but slopes were comparable for the speech-shaped noise. The quality of psychometric function fits was significantly better for the repeated-stimulus than the novel-stimulus procedure, even when comparing a single run of the repeated-stimulus procedure (using one list) to a run of the novel-stimulus procedure (using five lists). CONCLUSIONS: Repeating sentences at ascending TMRs is an efficient method for estimating thresholds and psychometric function slopes, both in terms of the number of sentences and the number of trials.

Development of speech glimpsing in synchronously and asynchronously modulated noise.

This study investigated development of the ability to integrate glimpses of speech in modulated noise. Noise was modulated synchronously across frequency or asynchronously such that when noise below 1300 Hz was "off," noise above 1300 Hz was "on," and vice versa. Asynchronous masking was used to examine the ability of listeners to integrate speech glimpses separated across time and frequency. The study used the Word Intelligibility by Picture Identification (WIPI) test and included adults, older children (age 8-10 yr) and younger children (5-7 yr). Results showed poorer masking release for the children than the adults for synchronous modulation but not for asynchronous modulation. It is possible that children can integrate cues relatively well when all intervals provide at least partial speech information (asynchronous modulation) but less well when some intervals provide little or no information (synchronous modulation). Control conditions indicated that children appeared to derive less benefit than adults from speech cues below 1300 Hz. This frequency effect was supported by supplementary conditions where the noise was unmodulated and the speech was low- or high-pass filtered. Possible sources of the developmental frequency effect include differences in frequency weighting, effective speech bandwidth, and the signal-to-noise ratio in the unmodulated noise condition.

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.

Effects of linguistic experience on the ability to benefit from temporal and spectral masker modulation.

Masked speech perception can often be improved by modulating the masker temporally and/or spectrally. These effects tend to be larger in normal-hearing listeners than hearing-impaired listeners, and effects of temporal modulation are larger in adults than young children [Hall et al. (2012). Ear Hear. 33, 340-348]. Initial reports indicate non-native adult speakers of the target language also have a reduced ability to benefit from temporal masker modulation [Stuart et al. (2010). J. Am. Acad. Aud. 21, 239-248]. The present study further investigated the effect of masker modulation on English speech recognition in normal-hearing adults who are non-native speakers of English. Sentence recognition was assessed in a steady-state baseline masker condition and in three modulated masker conditions, characterized by spectral, temporal, or spectro-temporal modulation. Thresholds for non-natives were poorer than those of native English speakers in all conditions, particularly in the presence of a modulated masker. The group differences were consistent across maskers when assessed in percent correct, suggesting that a single factor may limit the performance of non-native listeners similarly in all conditions.

Across-frequency envelope correlation discrimination and masked signal detection.

This study compared the dependence of comodulation masking release (CMR) and monaural envelope correlation perception (MECP) on the degree of envelope correlation for the same narrowband noise stimuli. Envelope correlation across noise bands was systematically varied by mixing independent bands with a base set of comodulated bands. The magnitude of CMR fell monotonically with reductions in envelope correlation, and CMR varied over a range of envelope correlations that were not discriminable from each other in the MECP paradigm. For complexes of 100-Hz-wide noise bands, discrimination thresholds in the MECP task were similar whether the standard was a comodulated set of noise bands or a completely independent set of noise bands. This was not the case for 25-Hz-wide noise bands. Although the data demonstrate that CMR and MECP exhibit different dependencies on the degree of envelope correlation, some commonality across the two phenomena was observed. Specifically, for 25-Hz-wide bands of noise, there was a robust relationship between individual listeners' sensitivity to decorrelation from an otherwise comodulated set of noise bands and the magnitude of CMR measured for those same comodulated noise bands.

Wideband monaural envelope correlation perception.

This study investigated monaural envelope correlation perception (Richards 1987) for noise bandwidths ranging from 25 to 1,600 Hz. The high-frequency side of the low band was fixed at 3,000 Hz and the low-frequency side of the high band was fixed at 3,500 Hz. When comodulated, the magnitude spectra of the pair of noise bands were either identical or reflected around the midpoint. Six listeners with normal hearing participated. Listeners showed similar performance for identical and reflected-spectrum conditions, with best performance usually occurring for bandwidths between 200 and 800 Hz. Results were considered in terms of envelope comparisons of waveforms at the outputs of multiple peripheral filters or envelope comparisons of waveforms at the outputs of central filters set to the bandwidths of the noise stimuli. Some aspects of the results were incompatible with the account based on multiple peripheral filters. However, the results of a supplementary condition involving the gating of band subregions indicated that this incompatibility could be accounted for by nonoptimal weighting of peripheral filter outputs.

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.

Monaural envelope correlation perception for bands narrower or wider than a critical band.

Monaural envelope correlation perception concerns the ability of listeners to discriminate stimuli based on the degree of correlation between the temporal envelopes of two or more frequency-separated bands of noise [Richards, J. Acoust. Soc. Am. 82, 1621-1630 (1987)]. Previous work has examined this ability for relatively narrow bandwidths, generally 100 Hz or less. The present experiment explored a wide range of bandwidths, from 25 to 1600 Hz, which included bands narrower and wider than a critical bandwidth. Stimuli were pairs of noise bands separated by a 500-Hz-wide spectral gap centered on 2250 Hz. The magnitude spectra of the pair of comodulated bands were either identical or reflected around the midpoint of the band, and performance was assessed with and without a low-pass noise masker. Although discrimination was best for intermediate bandwidths, mean performance was above chance for all bandwidths tested. Data were similar for stimuli with identical and reflected magnitude spectra, and for stimuli with and without the low-pass masker. The one exception was particularly good performance for intermediate-bandwidth stimuli with identical spectra, for which some listeners reported hearing a tonal cue. Results indicate that listeners are flexible in selecting spectral regions upon which to base across-frequency comparisons.

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.

Effects of masker envelope irregularities on tone detection in narrowband and broadband noise maskers.

Introducing coherent masker envelope modulation to frequency regions neighboring the signal frequency can reduce detection thresholds for a pure-tone signal. Verhey and Ernst (2009) reported that irregular masker modulation conferred greater benefit than regular modulation when the masker was broadband, but that there was no difference when the masker was narrowband. The present study evaluated two possible explanations for this result: one based on modulation adaptation and the other based on the introduction of relatively long-duration modulation minima in the irregular masker modulation condition. The first experiment replicated the results of Verhey and Ernst (2009), but also included conditions in which a 12.5-ms signal was presented in a 12.5-ms modulation minimum, which was exempted from envelope jitter. The second experiment used a continuous masker and suspended jitter during epochs associated with either a 12.5- or 87.5-ms signal. No benefit of masker envelope irregularity before or after the signal was observed in either experiment. These findings are inconsistent with an explanation based on modulation adaptation, implicating instead the introduction of relatively long-duration modulation minima in the large masking release obtained for a long-duration signal in an irregularly modulated masker.