Temporal Fine Structure Sensitivity Research Articles

The relationship between interaural delay in binaural gap detection and sensitivity to temporal fine structure in young adults with or without musical training experience.

Humans can detect the presence of a break in interaural correlation (BIC, also called binaural gap) even if a large interaural time delay (ITD) is introduced, which is important for detecting, recognizing, and localizing sounds in everyday environments. To investigate the relationship between interaural delay in binaural gap detection and the sensitivity of temporal fine structure (TFS), 40 young college students with normal hearing took the BIC delay threshold test, the TFS1 test (the test of monaural TFS sensitivity), and the TFS-AF test (the test of binaural TFS sensitivity). All participants were asked whether they had any musical training experience in their childhood. Results showed that the BIC delay threshold was significantly correlated with the TFS1 test (r =−0.426, p = 0.006), but not with the TFS-AF performance (r =−0.005, p = 0.997). The correlation between BIC delay threshold and monaural TFS sensitivity was observed in the non-music training group (r =−0.508, p = 0.010), but not in the music training group (r =−0.290, p = 0.295). These findings suggest that the interaural delay in binaural gap detection is related to the monaural sensitivity of TFS, this significant correlation was mainly found in young adults without musical training experience.

Speech in Noise: Implications of Age, Hearing Loss, and Cognition

Introduction: Individuals with hearing loss have reduced hearing sensitivity and may not adequately process the temporal cues in acoustic signals. Cognitive skills that decrease with aging and hearing loss contribute negatively on the ability to understand speech. Hence, they may experience communication problems in noisy environments. The aim of the study was to investigate the effect of sloping high-frequency hearing loss on speech perception in noise and to examine the impact of temporal and cognitive processing in young and middle-age adults. Methods: Speech in noise (SIN), temporal processing, and cognitive tests were conducted to hearing loss and normal hearing individuals aged 18–59 years. The measurements included the matrix sentence test, binaural temporal fine structure sensitivity (TFS) test, Visual Aural Digit Span (VADS), and Auditory Verbal Learning Test (AVLT). Twenty participants with normal hearing were recruited in the control group, whereas 20 participants with hearing loss at high frequencies were composed of the study group. Results: Hierarchical regression analysis for SIN was performed by entering 3 separate blocks of independent variables. We entered age and hearing loss into the first block, which explained a significant amount of variability in SIN (R2 = 0.72, p < 0.001). Block 2 was comprised of scores from TFS sensitivity test, and this independent variable characterized temporal processing (R2 change = 0.002, p < 0.001). Block 3 was consisted of scores from VADS test and AVLT; these variables characterized cognitive processing and accounted for a good portion of SIN variance (R2 change = 0.04, p < 0.001). The age, hearing loss, and VADS contributed independently in the presence of all independent variables. Conclusion: The final model accounted for 76.2% of the variance in SIN. The results suggested that sloping hearing loss, aging, and cognitive decline affected auditory performance, and the poor performance starts from an early age. Additionally, the findings indicated that a more comprehensive approach might be recommended to evaluate the listening skills and identify communication problems.

Relationships Among Temporal Fine Structure Sensitivity, Transient Storage Capacity, and Ultra-High Frequency Hearing Thresholds in Tinnitus Patients and Normal Adults of Different Ages.

BackgroundElderlies and tinnitus patients often find it challenging to process acoustic signals in noisy environments. The sensitivity to temporal fine structure (TFS), the transient storage capacity for TFS, and the ultra-high frequency (UHF) thresholds are all associated with aging-related damage, evidenced by speech-in-noise perception deficits. In the present study, we aimed to investigate the relationships among TFS sensitivity, transient storage capacity, and UHF thresholds in tinnitus patients and normal adults of different ages.MethodsIn the present study, 38 tinnitus patients (age ranging from 21 to 65) and 23 non-tinnitus adults (age ranging from 22 to 56) were enrolled, and some of their auditory indicators were examined, including the TFS-adaptive frequency (TFS-AF), break in interaural correlation (BIAC) delay threshold, and UHF thresholds.ResultsWe found no significant difference in TFS-AF thresholds and BIAC delay thresholds between the tinnitus group and normal group, while their relationships with age were more evident in the tinnitus group. Moreover, these two tests were only significantly correlated in the tinnitus group. UHF thresholds were significantly correlated with TFS-AF thresholds only in the tinnitus group, suggesting that the UHF hearing was positively associated with the TFS sensitivity.ConclusionThese findings indicated that the influencing factors, such as tinnitus and UHF thresholds, should be fully considered when examining age-related hearing decline, because the combination of tinnitus and poor UHF hearing might play a role in affecting hearing ability, such as TFS sensitivity.

Traditional Martial Arts and Shooting Training Have Different Effects on Auditory Fine Structure Processing Ability - Evidence from Behavioral Tests and fMRI

In this work, we explore the influence of traditional martial arts and shooting training on the ability of auditory Temporal Fine Structure (TFS) processing. Twenty-five college students participated in the experiment, including 8 traditional martial arts practitioners, 8 high-level shooting athletes, and 9 control groups without any regular exercise habits. The BIC (break in interaural correlation) delay threshold and TFS1 test were used to evaluate the transient storage capacity and sensitivity of TFS, respectively. An fMRI test was performed after the behavioral tests. The results found that the traditional martial arts group had stronger TFS sensitivity, while the shooting group had stronger TFS storage capacity and the performance of the behavioral tests of the shooting group is related to the fALFF value of the brain areas of interest. The effects of exercise training on hearing ability may have a specific neural basis and can be used for early intervention in potential hearing impairment.

Comparison of temporal fine structure sensitivity and concurrent vowel perception between children with and without reading disability

Background: Children with reading disabilities (RD) exhibit difficulty in perceiving speech in background noise due to poor auditory stream segregation. There is a dearth of literature on measures of temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities to assess auditory stream segregation in children with reading disabilities. Hence the present study compared temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities between children with and without reading deficits. Method: The present research consisted of a total number of 30 participants, 15 children with reading disabilities (RD) and fifteen typically developing (TD) children within the age range of 7-14 years and were designated as Group 1 and Group 2 respectively. Both groups were matched for age, grade, and classroom curricular instructions. The groups were evaluated for TFS and concurrent vowel perception abilities and the performance was compared using independent ‘t’ test and repeated measure ANOVA respectively. Results: Results revealed that the children with RD performed significantly (p &lt; 0.001) poorer than TD children on both TFS and concurrent vowel identification task. On concurrent vowel identification tasks, there was no significant interaction found between reading ability and F0 difference suggesting that the trend was similar in both the groups. Conclusion: The study concludes that the children with RD show poor temporal fine structure sensitivity and concurrent vowel identification scores compared to age and grade matched TD children owing to poor auditory stream segregation in children with RD.

Comparison of temporal fine structure sensitivity and concurrent vowel perception between children with and without reading disability

Background: Children with reading disabilities (RD) exhibit difficulty in perceiving speech in background noise due to poor auditory stream segregation. There is a dearth of literature on measures of temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities to assess auditory stream segregation in children with reading disabilities. Hence the present study compared temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities between children with and without reading deficits. Method: The present research consisted of a total number of 30 participants, 15 children with reading disabilities (RD) and fifteen typically developing (TD) children within the age range of 7-14 years and were designated as Group 1 and Group 2 respectively. Both groups were matched for age, grade, and classroom curricular instructions. The groups were evaluated for TFS and concurrent vowel perception abilities and the performance was compared using independent ‘t’ test and repeated measure ANOVA respectively. Results: Results revealed that the children with RD performed significantly (p < 0.001) poorer than TD children on both TFS and concurrent vowel identification task. On concurrent vowel identification tasks, there was no significant interaction found between reading ability and F0 difference suggesting that the trend was similar in both the groups. Conclusion: The study concludes that the children with RD show poor temporal fine structure sensitivity and concurrent vowel identification scores compared to age and grade matched TD children owing to poor auditory stream segregation in children with RD.

Development of binaural temporal fine structure sensitivity in children.

The highest frequency for which the temporal fine structure (TFS) of a sinewave can be compared across ears varies between listeners with an upper limit of about 1400 Hz for young normal-hearing adults (YNHA). In this study, binaural TFS sensitivity was investigated for 63 typically developing children, aged 5 years, 6 months to 9 years, 4 months using the temporal fine structure-adaptive frequency (TFS-AF) test of Füllgrabe, Harland, Sęk, and Moore [Int. J. Audiol. 56, 926-935 (2017)]. The test assesses the highest frequency at which an interaural phase difference (IPD) of ϕ° can be distinguished from an IPD of 0°. The values of ϕ were 30° and 180°. The starting frequency was 200 Hz. The thresholds for the children were significantly lower (worse) than the thresholds reported by Füllgrabe, Harland, Sęk, and Moore [Int. J. Audiol. 56, 926-935 (2017)] for YNHA. For both values of ϕ, the median age at which children performed above chance level was significantly higher (p < 0.001) than for those who performed at chance. For the subgroup of 40 children who performed above chance for ϕ = 180°, the linear regression analyses showed that the thresholds for ϕ = 180° increased (improved) significantly with increasing age (p < 0.001) with adult-like thresholds predicted to be reached at 10 years, 2 months of age. The implications for spatial release from masking are discussed.

Comparison of temporal fine structure sensitivity and concurrent vowel perception between children with and without reading disability.

Background: Children with reading deficits (RD) exhibit difficulty in perceiving speech in background noise due to poor auditory stream segregation. There is a dearth of literature on measures of temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities to assess auditory stream segregation in children with reading deficits. Hence the present study compared temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities between children with and without reading deficits. Method: The present research consisted of a total number of 30 participants, 15 children with reading deficits (RD) and fifteen typically developing (TD) children within the age range of 7-14 years and were designated as Group 1 and Group 2 respectively. Both groups were matched for age, grade, and classroom curricular instructions. The groups were evaluated for TFS and concurrent vowel perception abilities and the performance was compared using independent 't' test and repeated measure ANOVA respectively. Results: Results revealed that the children with RD performed significantly (p < 0.001) poorer than TD children on both TFS and concurrent vowel identification task. On concurrent vowel identification tasks, there was no significant interaction found between reading ability and F0 difference suggesting that the trend was similar in both the groups. Conclusion: The study concludes that the children with RD show poor temporal fine structure sensitivity and concurrent vowel identification scores compared to age and grade matched TD children owing to poor auditory stream segregation in children with RD.

Binaural sensitivity and release from speech-on-speech masking in listeners with and without hearing loss.

Listeners with sensorineural hearing loss routinely experience less spatial release from masking (SRM) in speech mixtures than listeners with normal hearing. Hearing-impaired listeners have also been shown to have degraded temporal fine structure (TFS) sensitivity, a consequence of which is degraded access to interaural time differences (ITDs) contained in the TFS. Since these "binaural TFS" cues are critical for spatial hearing, it has been hypothesized that degraded binaural TFS sensitivity accounts for the limited SRM experienced by hearing-impaired listeners. In this study, speech stimuli were noise-vocoded using carriers that were systematically decorrelated across the left and right ears, thus simulating degraded binaural TFS sensitivity. Both (1) ITD sensitivity in quiet and (2) SRM in speech mixtures spatialized using ITDs (or binaural release from masking; BRM) were measured as a function of TFS interaural decorrelation in young normal-hearing and hearing-impaired listeners. This allowed for the examination of the relationship between ITD sensitivity and BRM over a wide range of ITD thresholds. This paper found that, for a given ITD sensitivity, hearing-impaired listeners experienced less BRM than normal-hearing listeners, suggesting that binaural TFS sensitivity can account for only a modest portion of the BRM deficit in hearing-impaired listeners. However, substantial individual variability was observed.

Investigating the role of temporal fine structure in everyday hearing

Human listeners can derive substantial masking release when there are discrepancies in pitch or spatial location between the target and masking sounds. While the temporal fine-structure (TFS) in low-frequency sounds can convey information about both pitch and location, a nuanced debate exists in the literature about the role of these TFS cues in masking release. The long-term goal of the present study is to leverage individual differences to understand the role of TFS in everyday hearing. As a first step, we sought to measure individual TFS sensitivity using monaural frequency modulation (FM) and binaural interaural time difference (ITD) detection tasks. Preliminary data show large individual differences in these measures. Moreover, individual differences in ITD sensitivity were correlated with monaural FM sensitivity suggesting that monaural TFS coding can be a primary bottleneck determining binaural sensitivity. Alternately, both FM and ITD sensitivity variations could be reflecting common non-sensory factors (e.g., attention). To disambiguate between these hypotheses, we designed two passive EEG metrics of TFS coding. Follow-up experiments will compare individual differences in these perceptual and EEG measures to each other, and to speech-in-noise perception in complex environments.

Temporal Fine Structure Processing, Pitch, and Speech Perception in Adult Cochlear Implant Recipients.

The aim of the study was to investigate the link between temporal fine structure (TFS) processing, pitch, and speech perception performance in adult cochlear implant (CI) recipients, including bimodal listeners who may benefit better low-frequency (LF) temporal coding in the contralateral ear. The study participants were 43 adult CI recipients (23 unilateral, 6 bilateral, and 14 bimodal listeners). Two new LF pitch perception tests-harmonic intonation (HI) and disharmonic intonation (DI)-were used to evaluate TFS sensitivity. HI and DI were designed to estimate a difference limen for discrimination of tone changes based on harmonic or inharmonic pitch glides. Speech perception was assessed using the newly developed Italian Sentence Test with Adaptive Randomized Roving level (STARR) test where sentences relevant to everyday contexts were presented at low, medium, and high levels in a fluctuating background noise to estimate a speech reception threshold (SRT). Although TFS and STARR performances in the majority of CI recipients were much poorer than those of hearing people reported in the literature, a considerable intersubject variability was observed. For CI listeners, median just noticeable differences were 27.0 and 147.0 Hz for HI and DI, respectively. HI outcomes were significantly better than those for DI. Median STARR score was 14.8 dB. Better performers with speech reception thresholds less than 20 dB had a median score of 8.6 dB. A significant effect of age was observed for both HI/DI tests, suggesting that TFS sensitivity tended to worsen with increasing age. CI pure-tone thresholds and duration of profound deafness were significantly correlated with STARR performance. Bimodal users showed significantly better TFS and STARR performance for bimodal listening than for their CI-only condition. Median bimodal gains were 33.0 Hz for the HI test and 95.0 Hz for the DI test. DI outcomes in bimodal users revealed a significant correlation with unaided hearing thresholds for octave frequencies lower than 1000 Hz. Median STARR scores were 17.3 versus 8.1 dB for CI only and bimodal listening, respectively. STARR performance was significantly correlated with HI findings for CI listeners and with those of DI for bimodal listeners. LF pitch perception was found to be abnormal in the majority of adult CI recipients, confirming poor TFS processing of CIs. Similarly, the STARR findings reflected a common performance deterioration with the HI/DI tests, suggesting the cause probably being a lack of access to TFS information. Contralateral hearing aid users obtained a remarkable bimodal benefit for all tests. Such results highlighted the importance of TFS cues for challenging speech perception and the relevance to everyday listening conditions. HI/DI and STARR tests show promise for gaining insights into how TFS and speech perception are being limited and may guide the customization of CI program parameters and support the fine tuning of bimodal listening.

Binaural sensitivity to temporal fine structure and lateralization ability in children with suspected (central) auditory processing disorder

ObjectivePrevious studies have shown that a subgroup of children with suspected (central) auditory processing disorder (SusCAPD) have insufficient ability to use binaural cues to benefit from spatial processing. Thus, they experience considerable listening difficulties in challenging auditory environments, such as classrooms. Some researchers have also indicated the probable role of binaural temporal fine structure (TFS) in the perceptual segregation of target signal from noise and hence in speech perception in noise. Therefore, in the present study, in order to further investigate the underlying reason for listening problems against background noise in this group of children, their performance was measured using binaural TFS sensitivity test (TFS-LF) as well as behavioral auditory lateralization in noise test, both of which are based on binaural temporal cues processing. MethodsParticipants in this analytical study included 91 children with normal hearing and no listening problems and 41 children (9–12 years old) with SusCAPD who found it challenging to understand speech in noise. Initially, the ability to use binaural TFS was measured at three frequencies (250, 500 and 750Hz) in both the groups, and the results of preliminary evaluations were compared between normal children and those with SusCAPD who participated in the study. Thereafter, the binaural performance of the 16 children with SusCAPD who had higher thresholds than the normal group at all three frequencies tested in TFS-LF test was examined using the lateralization test in 7 spatial locations. ResultsTotal 16 of the 41 children with SusCAPD who participated in this study (39%) showed poor performance on the TFS-LF test at all three frequencies, compared to both normal children and other children in the APD group (p<0.05). Furthermore, children in the APD group with binaural TFS coding deficits at all three frequencies revealed significant differences in the lateralization test results compared to normal children (p<0.05). ConclusionFindings of the current study demonstrated that one of the underlying causes for the difficulty understanding speech in noisy environments experienced by a subgroup of children with SusCAPD can be the reduced ability to benefit from binaural TFS information. This study also showed that a reduced ability to use binaural TFS cues in the group of children with SusCAPD was accompanied by reduced binaural processing abilities in the lateralization test which also admit the presence of binaural temporal processing deficits in this group of children.

A two-path model of auditory modulation detection using temporal fine structure and envelope cues.

A model using temporal-envelope cues was previously developed to explain perceptual interference effects between amplitude modulation and frequency modulation (FM). As that model could not accurately predict FM sensitivity and the interference effects, temporal fine structure (TFS) cues were added to the model. Thus, following the initial stage of the model consisting of a linear filter bank simulating cochlear filtering, processing was split into an 'envelope path' based on envelope power cues and a 'TFS path' based on a measure of the distribution of time intervals between successive zero-crossings. This yielded independent detectability indices for envelope and TFS cues, which were optimally combined to produce a single decision statistic. Independent internal noises in the envelope and TFS paths were adjusted to match the data. Simulations indicate that TFS cues are required to account for FM data for young normal-hearing listeners and that TFS processing is impaired for both older normal-hearing and hearing-impaired listeners. The role of TFS was further assessed by relating the monaural FM sensitivity to measures of interaural phase difference, commonly assumed to rely on binaural TFS sensitivity. The model demonstrates that binaural TFS sensitivity is considerably lower than monaural TFS sensitivity. Similar to FM thresholds, interaural phase difference sensitivity declined with age and hearing loss, although higher degradations were observed in binaural temporal processing compared to monaural processing. Overall, this model provides a novel tool to explore the mechanisms involved in FM processing in the normal auditory system and the degradations in FM sensitivity with ageing and hearing loss.

The Association Between the Processing of Binaural Temporal-Fine-Structure Information and Audiometric Threshold and Age: A Meta-Analysis.

The ability to process binaural temporal fine structure (TFS) information, which influences the perception of speech in spatially distributed soundscapes, declines with increasing hearing loss and age. Because of the relatively small sample sizes used in previous studies, and the population-unrepresentative distribution of hearing loss and ages within study samples, it has been difficult to determine the relative and combined contributions of hearing loss and age. The aim of this study was to survey published and unpublished studies that assessed binaural TFS sensitivity using the TFS-low frequency (LF) test. Results from 19 studies were collated, yielding sample sizes of 147 to 648, depending on the test frequency. At least for the test frequency of 500 Hz, there were at least 67 listeners in each of four adult age groups and the distribution of audiometric thresholds at the test frequency within each group was similar to that for the population as a whole. Binaural TFS sensitivity declined with increasing age across the adult lifespan and with increasing hearing loss in old adulthood. For all test frequencies, both audiometric threshold and age were significantly negatively correlated with TFS-LF sensitivity (r ranging from −0.19 to −0.64) but the correlation was always significantly higher for age than for audiometric threshold. Regression analyses showed that the standardized regression coefficient was greater for age than for audiometric threshold, and that there was a significant interaction; the effect of increasing age among older listeners was greater when the hearing loss was ≥30 dB than when it was < 30 dB.

Evaluation of a Method for Determining Binaural Sensitivity to Temporal Fine Structure (TFS-AF Test) for Older Listeners With Normal and Impaired Low-Frequency Hearing.

The ability to process binaural temporal fine structure (TFS) information was assessed using the TFS-AF test (where AF stands for adaptive frequency) for 26 listeners aged 60 years or more with normal or elevated low-frequency audiometric thresholds. The test estimates the highest frequency at which a fixed interaural phase difference (IPD) of ϕ (varied here between 30° and 180°) can be discriminated from an IPD of 0°, with higher thresholds indicating better performance. A sensation level of 30 dB was used. All listeners were able to perform the task reliably, giving thresholds well above the lowest allowed frequency of 30 Hz. The duration of a run averaged 5 min. Repeated testing of the normal-hearing listeners showed no significant practice effects. Thresholds varied markedly across listeners, but their ranking was fairly consistent across values of ϕ. Thresholds decreased (worsened) with decreasing ϕ and were lower than for a group of young listeners tested in an earlier study. There were weak to moderate, negative correlations between TFS-AF thresholds and audiometric thresholds at low frequencies (125–1000 Hz) but not at high frequencies (4000–8000 Hz). In conclusion, the TFS-AF test yielded a graded measure of binaural TFS sensitivity for all listeners. This contrasts with the TFS-LF (low-frequency) test, which measures the smallest detectable shift in IPD for a fixed frequency. The absence of practice effects and a reasonably short administration time make the TFS-AF test a good candidate for the assessment of sensitivity to changes in binaural TFS for older listeners without or with hearing loss.

Development of a method for determining binaural sensitivity to temporal fine structure

Objective: To develop and evaluate a test of the ability to process binaural temporal-fine-structure (TFS) information. The test was intended to provide a graded measure of TFS sensitivity for all listeners. Design: Sensitivity to TFS was assessed at a sensation level of 30 dB using the established TFS-LF test at centre frequencies of 250, 500 and 750 Hz, and using the new TFS-AF test, in which the interaural phase difference (IPD) was fixed and the frequency was adaptively varied. IPDs varied from 30 to 180°. Study Sample: Nine young (19–25 years) and 23 older (47–84 years) listeners with normal hearing over the tested frequency range. Results: For the young listeners, thresholds on the TFS-AF test did not improve significantly with repeated testing. The rank-ordering of performance across listeners was independent of the size of the IPD, and moderate-to-strong correlations were observed between scores for the TFS-LF and TFS-AF tests. Older listeners who were unable to complete the TFS-LF test were all able to complete the TFS-AF test. Conclusions: No practice effects and strong correlations with an established test of binaural TFS sensitivity make the TFS-AF test a good candidate for the assessment of supra-threshold binaural processing.

The effect of tone-vocoding on spatial release from masking for old, hearing-impaired listeners

Old, hearing-impaired listeners generally benefit little from lateral separation of multiple talkers when listening to one of them. This study aimed to determine how spatial release from masking (SRM) in such listeners is affected when the interaural time differences (ITDs) in the temporal fine structure (TFS) are manipulated by tone-vocoding (TVC) at the ears by a master hearing aid system. Word recall was compared, with and without TVC, when target and masker sentences from a closed set were played simultaneously from the front loudspeaker (co-located) and when the maskers were played 45° to the left and right of the listener (separated). For 20 hearing-impaired listeners aged 64 to 86, SRM was 3.7 dB smaller with TVC than without TVC. This difference in SRM correlated with mean audiometric thresholds below 1.5 kHz, even when monaural TFS sensitivity (discrimination of frequency-shifts in identically filtered complexes) was partialed out, suggesting that low-frequency audiometric thresholds may be a good indicator of candidacy for hearing aids that preserve ITDs. The TVC difference in SRM was not correlated with age, pure-tone ITD thresholds, nor fundamental frequency difference limens, and only with monaural TFS sensitivity before control for low-frequency audiometric thresholds.

Relation Between Cochlear Mechanics and Performance of Temporal Fine Structure-Based Tasks.

This study examined whether the mechanical characteristics of the cochlea could influence individual variation in the ability to use temporal fine structure (TFS) information. Cochlear mechanical functioning was evaluated by swept-tone evoked otoacoustic emissions (OAEs), which are thought to comprise linear reflection by micromechanical impedance perturbations, such as spatial variations in the number or geometry of outer hair cells, on the basilar membrane (BM). Low-rate (2Hz) frequency modulation detection limens (FMDLs) were measured for carrier frequency of 1000Hz and interaural phase difference (IPD) thresholds as indices of TFS sensitivity and high-rate (16Hz) FMDLs and amplitude modulation detection limens (AMDLs) as indices of sensitivity to non-TFS cues. Significant correlations were found among low-rate FMDLs, low-rate AMDLs, and IPD thresholds (R=0.47-0.59). A principal component analysis was used to show a common factor that could account for 81.1, 74.1, and 62.9% of the variance in low-rate FMDLs, low-rate AMDLs, and IPD thresholds, respectively. An OAE feature, specifically a characteristic dip around 2-2.5kHz in OAE spectra, showed a significant correlation with the common factor (R=0.54). High-rate FMDLs and AMDLs were correlated with each other (R=0.56) but not with the other measures. The results can be interpreted as indicating that (1) the low-rate AMDLs, as well as the IPD thresholds and low-rate FMDLs, depend on the use of TFS information coded in neural phase locking and (2) the use of TFS information is influenced by a particular aspect of cochlear mechanics, such as mechanical irregularity along the BM.

Heritability of non-speech auditory processing skills.

Recent insight into the genetic bases for autism spectrum disorder, dyslexia, stuttering, and language disorders suggest that neurogenetic approaches may also reveal at least one etiology of auditory processing disorder (APD). A person with an APD typically has difficulty understanding speech in background noise despite having normal pure-tone hearing sensitivity. The estimated prevalence of APD may be as high as 10% in the pediatric population, yet the causes are unknown and have not been explored by molecular or genetic approaches. The aim of our study was to determine the heritability of frequency and temporal resolution for auditory signals and speech recognition in noise in 96 identical or fraternal twin pairs, aged 6-11 years. Measures of auditory processing (AP) of non-speech sounds included backward masking (temporal resolution), notched noise masking (spectral resolution), pure-tone frequency discrimination (temporal fine structure sensitivity), and nonsense syllable recognition in noise. We provide evidence of significant heritability, ranging from 0.32 to 0.74, for individual measures of these non-speech-based AP skills that are crucial for understanding spoken language. Identification of specific heritable AP traits such as these serve as a basis to pursue the genetic underpinnings of APD by identifying genetic variants associated with common AP disorders in children and adults.

Age-Dependent Changes in Temporal-Fine-Structure Processing in the Absence of Peripheral Hearing Loss

In this study, the author sought to investigate if and when the ability to process temporal-fine-structure (TFS) cues deteriorates with age in adults with audiometrically normal hearing sensitivity. Using a cross-sectional design, the author assessed TFS sensitivity in 102 normal-hearing adults sampled from across the entire range of adulthood (ages 18-90 years), using 2 psychophysical tests for the assessment of within- and across-ear TFS processing. Both types of TFS sensitivity (monaural and binaural) declined gradually starting in young adulthood, with the earliest significant deficit already apparent in early midlife (i.e., between ages 40 and 49 years). TFS sensitivity was not correlated with absolute sensitivity at the test frequency. Some suprathreshold auditory processing abilities decline throughout adulthood, even when an individual's peripheral hearing is clinically normal. These deficits are not captured by a conventional, audiometric hearing assessment but may contribute to the increasing difficulties with age to identify speech in noisy environments. From a methodological point of view, the existence of such age effects warrants the use of age-matched participant groups when comparing normal and impaired peripheral hearing.