Normal-hearing Young Adults Research Articles

The Role of Age-Related Declines in Subcortical Auditory Processing in Speech Perception in Noise.

Older adults, even those without hearing impairment, often experience increased difficulties understanding speech in the presence of background noise. This study examined the role of age-related declines in subcortical auditory processing in the perception of speech in different types of background noise. Participants included normal-hearing young (19 – 29 years) and older (60 – 72 years) adults. Normal hearing was defined as pure-tone thresholds of 25 dB HL or better at octave frequencies from 0.25 to 4 kHz in both ears and at 6 kHz in at least one ear. Speech reception thresholds (SRTs) to sentences were measured in steady-state (SS) and 10-Hz amplitude-modulated (AM) speech-shaped noise, as well as two-talker babble. In addition, click-evoked auditory brainstem responses (ABRs) and envelope following responses (EFRs) in response to the vowel /ɑ/ in quiet, SS, and AM noise were measured. Of primary interest was the relationship between the SRTs and EFRs. SRTs were significantly higher (i.e., worse) by about 1.5 dB for older adults in two-talker babble but not in AM and SS noise. In addition, the EFRs of the older adults were less robust compared to the younger participants in quiet, AM, and SS noise. Both young and older adults showed a “neural masking release,” indicated by a more robust EFR at the trough compared to the peak of the AM masker. The amount of neural masking release did not differ between the two age groups. Variability in SRTs was best accounted for by audiometric thresholds (pure-tone average across 0.5–4 kHz) and not by the EFR in quiet or noise. Aging is thus associated with a degradation of the EFR, both in quiet and noise. However, these declines in subcortical neural speech encoding are not necessarily associated with impaired perception of speech in noise, as measured by the SRT, in normal-hearing older adults.

The development and evaluation of the Finnish digit triplet test

Objectives: The aim of the study was to develop a reliable and easily accessible screening test for primary detection of hearing impairment.Methods: Digits 0–9 were used to form quasirandom digit triplets. First, digit specific intelligibility functions and speech recognition thresholds (SRTs) were determined. To homogenize the test material digits with steep intelligibility function slopes were chosen and level correction up to ±2 dB were applied to the digits as needed. Evaluation measurements were performed to check for systematic differences in intelligibility between the test lists and to obtain normative reference function for normal-hearing listeners.Results: The mean SRT and the final slope of the test lists were −10.8 ± 0.1 dB signal-to-noise ratio (SNR) and 21.7 ± 1.8%/dB, respectively (measurements at constant level; inter-list variability). The mean SRT and slope of the test subjects were −10.8 ± 0.5 dB SNR and 23.4 ± 5.2%/dB (measurements at constant level; inter-subject variability). The mean SRT for normal-hearing young adults for a single adaptive measurement is −9.8 ± 0.9 dB SNR.Conclusion: The Finnish digit triplet test is the first self-screening hearing test in the Finnish language. It was developed according to current standards, and it provides reliable and internationally comparable speech intelligibility measurements.

On the Relationship Between Musicianship and Contralateral Suppression of Transient-Evoked Otoacoustic Emissions.

The medial olivocochlear (MOC) efferent reflex that modulates outer hair cell function has been shown to be more robust in musicians versus nonmusicians as evidenced in greater contralateral suppression of transient-evoked otoacoustic emissions (TEOAEs). All previous research comparing musical ability and MOC efferent strength has defined musicianship dichotomously (i.e., high-level music students or professional classical musicians versus nonmusicians). The objective of the study was to further explore contralateral suppression of TEOAEs among adults with a full spectrum of musicianship ranging from no history of musicianship to professional musicians. Musicianship was defined by both self-report and with an objective test to quantify individual differences in perceptual music skills. A single-factor between-subjects and correlational research designs were employed. Forty-five normal-hearing young adults participated. Participants completed a questionnaire concerning their music experience and completed the Brief Profile of Music Perception Skills (PROMS) to quantify perceptual musical skills across multiple musical domains (i.e., accent, melody, tempo, and tuning). TEOAEs were evaluated with 60 dB peak equivalent sound pressure level click stimuli with and without a contralateral 65 dB sound pressure level white noise suppressor. TEOAE suppression was expressed in two ways, absolute TEOAE suppression in dB and a normalized index of TEOAE suppression (i.e., percentage of suppression). Participants who considered themselves musicians scored significantly higher on all subscales and total Brief PROMS score (p < 0.05). There was no statistically significant difference between musicians and nonmusicians in absolute TEOAE suppression or percentage of TEOAE suppression (p > 0.05). There were no statistically significant correlations or linear predictive relationships between subscale or total Brief PROMS scores with absolute and percentage of TEOAE suppression (p > 0.05). The findings do not support the notion of a graded enhancement of MOC efferent suppression among adults with varied degrees of musicianship from nonmusicians to professional musicians.

Within- and Across-Subject Variability of Repeated Measurements of Medial Olivocochlear-Induced Changes in Transient-Evoked Otoacoustic Emissions

Measurement of changes in transient-evoked otoacoustic emissions (TEOAEs) caused by activation of the medial olivocochlear reflex (MOCR) may have clinical applications, but the clinical utility is dependent in part on the amount of variability across repeated measurements. The purpose of this study was to investigate the within- and across-subject variability of these measurements in a research setting as a step toward determining the potential clinical feasibility of TEOAE-based MOCR measurements. In 24 normal-hearing young adults, TEOAEs were elicited with 35 dB SL clicks and the MOCR was activated by 35 dB SL broadband noise presented contralaterally. Across a 5-week span, changes in both TEOAE amplitude and phase evoked by MOCR activation (MOC shifts) were measured at four sessions, each consisting of four independent measurements. Efforts were undertaken to reduce the effect of potential confounds, including slow drifts in TEOAE amplitude across time, activation of the middle-ear muscle reflex, and changes in subjects' attentional states. MOC shifts were analyzed in seven 1/6-octave bands from 1 to 2 kHz. The variability of MOC shifts was analyzed at the frequency band yielding the largest and most stable MOC shift at the first session. Within-subject variability was quantified by the size of the standard deviations across all 16 measurements. Across-subject variability was quantified as the range of MOC shift values across subjects and was also described qualitatively through visual analyses of the data. A large majority of MOC shifts in subjects were statistically significant. Most subjects showed stable MOC shifts across time, as evidenced by small standard deviations and by visual clustering of their data. However, some subjects showed within- and across-session variability that could not be explained by changes in hearing status, middle ear status, or attentional state. Simulations indicated that four baseline measurements were sufficient to predict the expected variability of subsequent measurements. However, the measured variability of subsequent MOC shifts in subjects was often larger than expected (based on the variability present at baseline), indicating the presence of additional variability at subsequent sessions. Results indicated that a wide range of within- and across-subject variability of MOC shifts was present in a group of young normal-hearing individuals. In some cases, very large changes in MOC shifts (e.g., 1.5 to 2 dB) would need to occur before one could attribute the change to either an intervention or pathology, rather than to measurement variability. It appears that MOC shifts, as analyzed in the present study, may be too variable for clinical use, at least in some individuals. Further study is needed to determine the extent to which changes in MOC shifts can be reliably measured across time for clinical purposes.

Gaps-in-Noise Measurement of the Elderly as a Function of Stimulus Level

Purpose: The gaps-in-noise (GIN) test was developed as a clinical evaluation of temporal resolution. In the GIN test, a sensation level of 50 dB SL was recommended as a standard clinical presentation level to ensure stimulus audibility. It has been reported that the stimulus level less than 30 dB SL should not be used as presentation level to verify a proper level for administration of GIN test. Given that the previous finding was based on the data of young normal-hearing adults, the present study aimed to compare the GIN results as a function of stimulus level in listener groups differing in age and hearing sensitivity. Methods: Participants were 10 young normal-hearing (YNH), 12 elderly normal-hearing, and 12 elderly hearing-impaired (EHI) listeners. GIN was administered at 20, 30, 40, and 50 dB SL. The performance was determined from both the approximate threshold and the percentage of correct gap. Results: As results, both approximate threshold and percent correct in GIN results were measured. Results showed that, overall, both the threshold as well as the percent correct in GIN improved with increasing stimulus level. Across groups, EHI showed the poorest results from GIN test, with the best performance in YNH. EHI listeners with greater hearing loss at higher frequencies (2-8 kHz) were poorer at detecting gaps in noise. Across a range of stimulus level (20-50 dB SL), the GIN performance between 40 and 50 dB SL did not differ in all listener groups. Conclusion: A sensation level of 35-50 dB may be applicable to the elderly with normal hearing or slight-to-mild degree of hearing loss, without significant change in GIN performance.

The intelligibility of interrupted and temporally altered speech: Effects of context, age, and hearing loss.

Temporal constraints on the perception of interrupted speech were investigated by comparing the intelligibility of speech that was periodically gated (PG) and subsequently either temporally compressed (PGTC) by concatenating remaining speech fragments or temporally expanded (PGTE) by doubling the silent intervals between speech fragments. Experiment 1 examined the effects of PGTC and PGTE at different gating rates (0.5 -16 Hz) on the intelligibility of words and sentences for young normal-hearing adults. In experiment 2, older normal-hearing (ONH) and older hearing-impaired (OHI) adults were tested with sentences only. The results of experiment 1 indicated that sentences were more intelligible than words. In both experiments, PGTC sentences were less intelligible than either PG or PGTE sentences. Compared with PG sentences, the intelligibility of PGTE sentences was significantly reduced by the same amount for ONH and OHI groups. Temporal alterations tended to produce a U-shaped rate-intelligibility function with a dip at 2-4 Hz, indicating that temporal alterations interacted with the duration of speech fragments. The present findings demonstrate that both aging and hearing loss negatively affect the overall intelligibility of interrupted and temporally altered speech. However, a mild-to-moderate hearing loss did not exacerbate the negative effects of temporal alterations associated with aging.

Level considerations for chimeric processing: Temporal envelope and fine structure contributions to speech intelligibility.

Chimeric processing is used to assess the respective role of the acoustic temporal envelope (ENV) and the temporal fine structure (TFS) by adding noise to either component. An acoustic analysis demonstrates that adding noise to the ENV results in noise degradation of the ENV and overall signal attenuation, whereas adding noise to the TFS results in only noise degradation of the TFS. Young normal hearing adults were then tested using a modified chimeric strategy to maintain speech levels. Results partially confirm the primary role of the ENV in determining speech intelligibility but demonstrate significant TFS contributions during selective ENV masking.

Association between auditory pathway efferent functions and genotoxicity in young adults

AbstractEfferent auditory pathways modulate outer hair cells of the cochlea, protect against noise, and improve the detection of sound sources in noisy environments. Genotoxicity is DNA damage.Aim: To study the association between auditory pathway efferent functions with genotoxic markers. The study also considered smoking and gender as two main variables.Methods: A prospective-clinical, quantitative, cross-sectional, contemporary study. The function of efferent auditory pathways and genotoxicity tests in 60 healthy young subjects were assessed.Results: The mean age of subjects was 24.86 years +/- 3.68 years; there were 30 males and 30 females, 15 of each gender smokers and 15 non-smokers. Male smokers had a higher incidence of DPOEA suppression effect at 2000 and 6000 Hz in the left ear; female smokers had a higher prevalence of complaints of difficulty to hear in noisy environments; smokers and women had a higher mean DNA damage; subjects with complaints of hearing loss and tinnitus had higher genotoxicity.Conclusions: In young normal-hearing adults that complain about efferent auditory pathways functions, such as tinnitus and hearing impairment, there are possible associations with genotoxicity; interactions between gender and smoking are considered.

Nonlinear feature extraction for objective classification of complex auditory brainstem responses to diotic perceptually critical consonant-vowel syllables.

To examine if nonlinear feature extraction method yields appropriate results in complex brainstem response classification of three different consonant vowels diotically presented in normal Persian speaking adults. Speech-evoked auditory brainstem responses were obtained in 27 normal hearing young adults by using G.tec EEG recording system. 170ms synthetic consonant-vowel stimuli /ba/, /da/, /ga/ were presented binaurally and the recurrence quantification analysis was performed on the responses. The recurrence time of second type was proposed as a suitable feature. ANOVA was also used for testing the significance of extracted feature. Post-comparison statistical method was used for showing which means are significantly different from each other. Dimension embedding and state space reconstruction were helpful for visualizing nonlinearity in auditory system. The proposed feature was successful in the objective classification of responses in window time 20.1-35.3ms, which belonged to formant transition period of stimuli. Also the p value behavior of recurrence time of second type feature as a discriminant feature was close to the nature of the response that includes transient and sustained parts. On the other hand, the /ba/ and /ga/ classification period was wider than the others. The extracted feature shown in this paper is helpful for the objective of distinguishing individuals with auditory processing disorders in the structurally similar voices. On the other hand, differing nonlinear feature is meaningful in a special region of response, equal to formant transition period, and this feature is related to the state space changes of brainstem response. It can be assumed that more information is within this region of signal and it is a sign of processing role of brainstem. The state changes of system are dependent on input stimuli, so the existence of top down feedback from cortex to brainstem forces the system to act differently.

Temporal integration reflected by frequency following response in auditory brainstem.

Auditory temporal integration (ATI) has been widely described in psychoacoustic studies, especially for loudness perception. Loudness increases with increasing sound duration for durations up to a time constant about 100 ~ 200 ms, and then loudness becomes saturated with more duration increase. However, the electrophysiological mechanism underlying the ATI phenomenon has not been well understood. To investigate ATI at the brainstem level of auditory system and its relationship to cortical and behavioral ATI, frequency follow response (FFR) was acquired in our study. Simultaneously, ATI in auditory cortex was evaluated by cortical response P1. Behavioral loudness and electrophysiological measures were estimated from normal-hearing young adults for vowel /a/ whose durations varied from 50 ms to 175 ms. Significant effects of stimulus duration were found both on FFR and P1 amplitudes. Linear regression analysis revealed that as stimulus duration increased, brainstem FFR amplitude was significantly associated with cortical P1 amplitude and behavioral loudness, which confirmed the existence of temporal integration in auditory brainstem. Moreover, behavioral loudness ATI was better predicted using brainstem and cortical measures together than merely using each one separately, indicating an interplay and coordination for ATI across the three levels along auditory pathway.

Indexical properties influence time-varying amplitude and fundamental frequency contributions of vowels to sentence intelligibility

The present study investigated how non-linguistic, indexical information about talker identity interacts with contributions to sentence intelligibility by the time-varying amplitude (temporal envelope) and fundamental frequency (F0). Young normal-hearing adults listened to sentences that preserved the original consonants but replaced the vowels with a single vowel production. This replacement vowel selectively preserved amplitude or F0 cues of the original vowel, but replaced cues to phonetic identity. Original vowel duration was always preserved. Three experiments investigated indexical contributions by replacing vowels with productions from the same or different talker, or by acoustically morphing the original vowel. These stimulus conditions investigated how vowel suprasegmental and indexical properties interact and contribute to intelligibility independently from phonetic information. Results demonstrated that indexical properties influence the relative contribution of suprasegmental properties to sentence intelligibility. F0 variations are particularly important in the presence of conflicting indexical information. Temporal envelope modulations significantly improve sentence intelligibility, but are enhanced when either indexical or F0 cues are available. These findings suggest that F0 and other indexical cues may facilitate perceptually grouping suprasegmental properties of vowels with the remainder of the sentence. Temporal envelope modulations of vowels may contribute to intelligibility once they are successfully integrated with the preserved signal.

Discrimination of Stochastic Frequency Modulation by Cochlear Implant Users.

Past work has shown that low-rate frequency modulation (FM) may help preserve signal coherence, aid segmentation at word and syllable boundaries, and benefit speech intelligibility in the presence of a masker. This study evaluated whether difficulties in speech perception by cochlear implant (CI) users relate to a deficit in the ability to discriminate among stochastic low-rate patterns of FM. This is a correlational study assessing the association between the ability to discriminate stochastic patterns of low-rate FM and the intelligibility of speech in noise. Thirteen postlingually deafened adult CI users participated in this study. Using modulators derived from 5-Hz lowpass noise applied to a 1-kHz carrier, thresholds were measured in terms of frequency excursion both in quiet and with a speech-babble masker present, stimulus duration, and signal-to-noise ratio in the presence of a speech-babble masker. Speech perception ability was assessed in the presence of the same speech-babble masker. Relationships were evaluated with Pearson product-moment correlation analysis with correction for family-wise error, and commonality analysis to determine the unique and common contributions across psychoacoustic variables to the association with speech ability. Significant correlations were obtained between masked speech intelligibility and three metrics of FM discrimination involving either signal-to-noise ratio or stimulus duration, with shared variance among the three measures accounting for much of the effect. Compared to past results from young normal-hearing adults and older adults with either normal hearing or a mild-to-moderate hearing loss, mean FM discrimination thresholds obtained from CI users were higher in all conditions. The ability to process the pattern of frequency excursions of stochastic FM may, in part, have a common basis with speech perception in noise. Discrimination of differences in the temporally distributed place coding of the stimulus could serve as this common basis for CI users.

Isolating informational masking in both pure and complex tone sequences.

Interference between a target and simultaneous maskers occurs both at the cochlear level through energetic masking and more centrally through informational masking (IM). Hence, quantifying the amount of IM requires a strict control of the energetic component. Presenting target and maskers on different sides (i.e., dichotically) reduces energetic masking but provides listeners with important lateralization cues that also drastically reduce IM. The main purpose of this study (Experiment 1) was to evaluate a "switch" manipulation aiming at restoring most of the IM despite dichotic listening. Experiment 2 was designed to investigate the source of the difficulty induced by this switching dichotic condition. In Experiment 1, the authors presented 60 normal-hearing young adults with a detection task in which a regularly repeating target was embedded in a randomly varying background masker. The authors evaluated spatial masking release induced by three different dichotic listening conditions in comparison with a diotic baseline. Dichotic stimuli were presented in either a nonswitching or a switching condition. In the latter case, the presentation sides of dichotic target and maskers alternated several times throughout 10 sec sequences. The impact of the number of switches on IM was investigated parametrically, with both pure and complex tone sequences. In Experiment 2, the authors compared performance of 13 young, normal-hearing listeners in a monotic and dichotic version of the rapidly switching condition, using pure-tone sequences. When target and maskers switched rapidly within sequences, IM was significantly stronger than in nonswitching dichotic sequences and was comparable with the masking effect induced by diotic sequences. Furthermore, Experiment 2 suggests that rapidly switching target and maskers prevent listeners from relying on lateralization cues inherent to the dichotic condition, hence preserving important amounts of IM. This paradigm thus provides an original tool to isolate IM in signal and maskers having overlapping spectra.

The influence of cochlear spectral processing on the timing and amplitude of the speech-evoked auditory brain stem response

The speech-evoked auditory brain stem response (speech ABR) is widely considered to provide an index of the quality of neural temporal encoding in the central auditory pathway. The aim of the present study was to evaluate the extent to which the speech ABR is shaped by spectral processing in the cochlea. High-pass noise masking was used to record speech ABRs from delimited octave-wide frequency bands between 0.5 and 8 kHz in normal-hearing young adults. The latency of the frequency-delimited responses decreased from the lowest to the highest frequency band by up to 3.6 ms. The observed frequency-latency function was compatible with model predictions based on wave V of the click ABR. The frequency-delimited speech ABR amplitude was largest in the 2- to 4-kHz frequency band and decreased toward both higher and lower frequency bands despite the predominance of low-frequency energy in the speech stimulus. We argue that the frequency dependence of speech ABR latency and amplitude results from the decrease in cochlear filter width with decreasing frequency. The results suggest that the amplitude and latency of the speech ABR may reflect interindividual differences in cochlear, as well as central, processing. The high-pass noise-masking technique provides a useful tool for differentiating between peripheral and central effects on the speech ABR. It can be used for further elucidating the neural basis of the perceptual speech deficits that have been associated with individual differences in speech ABR characteristics.

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

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. 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. 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). 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.

Perceptual factors contribute more than acoustical factors to sound localization abilities with virtual sources.

Human sound localization abilities rely on binaural and spectral cues. Spectral cues arise from interactions between the sound wave and the listener's body (head-related transfer function, HRTF). Large individual differences were reported in localization abilities, even in young normal-hearing adults. Several studies have attempted to determine whether localization abilities depend mostly on acoustical cues or on perceptual processes involved in the analysis of these cues. These studies have yielded inconsistent findings, which could result from methodological issues. In this study, we measured sound localization performance with normal and modified acoustical cues (i.e., with individual and non-individual HRTFs, respectively) in 20 naïve listeners. Test conditions were chosen to address most methodological issues from past studies. Procedural training was provided prior to sound localization tests. The results showed no direct relationship between behavioral results and an acoustical metrics (spectral-shape prominence of individual HRTFs). Despite uncertainties due to technical issues with the normalization of the HRTFs, large acoustical differences between individual and non-individual HRTFs appeared to be needed to produce behavioral effects. A subset of 15 listeners then trained in the sound localization task with individual HRTFs. Training included either visual correct-answer feedback (for the test group) or no feedback (for the control group), and was assumed to elicit perceptual learning for the test group only. Few listeners from the control group, but most listeners from the test group, showed significant training-induced learning. For the test group, learning was related to pre-training performance (i.e., the poorer the pre-training performance, the greater the learning amount) and was retained after 1 month. The results are interpreted as being in favor of a larger contribution of perceptual factors than of acoustical factors to sound localization abilities with virtual sources.

Adaptive tests of temporal resolution: Comparison with the gaps-in-noise test in normal-hearing young adults

Objective: Auditory processing disorder patients may have deficits in auditory temporal resolution. This study explored: (1) the ear specific norms for young adults using the adaptive tests of temporal resolution (ATTR); (2) the reliability of ATTR using two different modes of stimuli presentation; and (3) the concurrent validity of ATTR with reference to the gaps-in-noise (GIN) test. Design: GIN and ATTR were administered through a standard audiometer and headphones. As ATTR can also be completed using a computer with commercially available headphones, thresholds from these two variants were compared. Study sample: Thirty normal-hearing young adults were recruited. Results: The mean ATTR gap detection thresholds (GDTs) derived under audiometer administration were 4.60 ms (SD 1.49) and 4.97 ms (SD 1.98) for the left and right ear, respectively. The approximated threshold (A. th.), an equivalent measure to the GDT in the GIN, mean values were 5.37 ms (SD 0.98) and 5.33 ms (SD 1.07) for left and right ears, respectively. No significant threshold difference was found between the ATTR variants. A positive, moderate correlation was found, and Bland-Altman plot analysis revealed good agreement, between GDT and A.th. Conclusions: ATTR and GIN results were moderately associated. Moreover, the ATTR was found to have high test-retest reliability and high specificity for the current participants.

Estimates of cochlear compression using distortion product otoacoustic emissions and growth of forward masking.

The authors investigated the relationship between behavioral and physiologic estimates of cochlear compression. Cochlear compression was estimated in distortion product otoacoustic emission (DPOAE) fine structure minima and maxima near 4 kHz. The composite DPOAE response and separated generator and reflection components yielded three estimates in four young adults with normal hearing. DPOAE estimates were compared to behavioral compression estimates derived using a growth of forward masking (GOFM) paradigm. The DPOAE primary tone f2 and GOFM signal were identical and selected individually based on placement in a DPOAE fine structure minimum. Across participants, DPOAE compression estimates derived from the generator component were most similar to estimates derived from the GOFM paradigm and did not vary with DPOAE fine structure. These results suggest that the generator component may provide a quick, reliable estimate of cochlear compression in humans. This may prove useful in populations that cannot give behavioral responses.

Effects of consecutive trials and test-retest reliability of 1000-Hz tympanometry in adults

Objective: To investigate the effect of consecutive 1000-Hz tympanometry testing on admittance measures, and examine test-retest reliability. Design: Repeated measures with eight trials of 1000-Hz Ya and Ba/Ga tympanometry, respectively, in two ears of each subject, followed by repeated 226-Hz tympanometry. Study sample: Twenty-seven normal-hearing young adults. Results: For single-peak tympanograms, peak Ytm and Gtm systematically increased across trials with a mean change of 8% and 15% at Trial 8, respectively, whereas Btm increased marginally. For notched tympanograms, peak Ytm and Btm decreased by 23% and 162% at Trial 8, and Gtm in two cases also decreased (10% on average). Trial 2 and 3 contributed 50% to 70% of the total changes. Test-retest differences of subsequently acquired 1000- and 226-Hz tympanograms were smaller than previously reported. Conclusions: Consecutive testing significantly alters middle-ear admittance in 1000-Hz tympanometry. The outcome is contingent on tympanogram pattern and admittance component: Increase of peak Ytm and Gtm in single-peak tympanograms and decrease of all measures in notched tympanograms. The present results complement previous studies on our understanding of the mechanism underlying this effect: a decrease of middle-ear stiffness. The effect of repetitive tympanometry should be accounted for in research involving sequential testing.

Binaural interaction in the auditory brainstem response: A normative study

ObjectiveBinaural interaction can be investigated using auditory evoked potentials. A binaural interaction component can be derived from the auditory brainstem response (ABR–BIC) and is considered evidence for binaural interaction at the level of the brainstem. Although click ABR–BIC has been investigated thoroughly, data on 500Hz tone-burst (TB) ABR–BICs are scarce. In this study, characteristics of click and 500Hz TB ABR–BICs are described. Furthermore, reliability of both click and 500Hz TB ABR–BIC are investigated. MethodsEighteen normal hearing young adults (eight women, ten men) were included. ABRs were recorded in response to clicks and 500Hz TBs. ABR–BICs were derived by subtracting the binaural response from the sum of the monaural responses measured in opposite ears. ResultsGood inter-rater reliability is obtained for both click and 500Hz TB ABR–BICs. The most reliable peak in click ABR–BIC occurs at a mean latency of 6.06ms (SD 0.354ms). Reliable 500Hz TB ABR–BIC are obtained with a mean latency of 9.47ms (SD 0.678ms). Amplitudes are larger for 500Hz TB ABR–BIC than for clicks. ConclusionThe most reliable peak in click ABR–BIC occurs at the downslope of wave V. Five hundred Hertz TB ABR–BIC is characterized by a broad positivity occurring at the level of wave V. SignificanceThe ABR–BIC is a useful technique to investigate binaural interaction in certain populations. Examples are bilateral hearing aid users, bilateral cochlear implant users and bimodal listeners. The latter refers to the combination of unilateral cochlear implantation and contralateral residual hearing. The majority of these patients have residual hearing in the low frequencies. The current study suggests that 500Hz TB ABR–BIC may be a suitable technique to assess binaural interaction in this specific population of cochlear implant users.