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Auditory steady-state responses (ASSRs) recorded with simultaneous presentation of multiple tones modulated from 77-105 Hz exhibit frequency specificity and can be acquired with monotic or dichotic stimulation. This study examined the frequency specificity and dichotic characteristics of 40 Hz ASSRs recorded with amplitude-modulated (AM) probe tones and unmodulated (UM) or AM interfering tones in 27 normal-hearing adults. The effects on ASSR amplitudes of monotically or dichotically presented interfering tones of various frequency, modulation depth, and modulation rate were studied. Significant decreases in ASSR amplitudes occurred when the UM interfering tone was monotic, higher in frequency, and approximately within an octave of the probe tone. ASSR amplitudes were also reduced when the AM interfering tone was monotic and modulated at a lower depth and was an octave above the probe tone. Probe and interfering AM tones modulated at different rates produced similar reductions in amplitude for ASSRs acquired with monotic and dichotic stimulation. The findings of this study contribute to clarifying the carrier and temporal envelope interactions between tonal stimuli. Description of the effects of these stimulus parameters on 40 Hz ASSRs can benefit clinical applications of this technique, including evaluating auditory function in adults not capable of participating in behavioral audiometric tests. [ABSTRACT FROM AUTHOR]

In the present study, hexagonal structured borate phosphors BaLaB 9 O 16 were prepared using a combustion method with colour-tunable emission properties achieved by varying the doping concentration of Eu 3+ and Tb 3+ in the cluster. The as-prepared materials were analyzed for structural and morphological parameters through X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) studies. Tuning of colour was predicted through the photoluminescence and photoluminescence excitation spectra of the materials that showed good green and red emissions when doped with Tb 3+ and Eu 3+ , respectively, whereas the emission of the co-doped sample (Eu 3+ and Tb 3+ ) can be varied from the green region to red region by varying the excitation range from 207 to 254  nm., (© 2021 John Wiley & Sons, Ltd.)

Purpose: Compared to photon-based radiotherapy, protons deliver less radiation to healthy tissue resulting in the potential reduction of late complications such as sensorineural hearing loss (SNHL). We report early auditory outcomes in children treated with proton radiotherapy (PRT) for craniopharyngioma., Method: Conventional frequency (CF = 0.25-8.0 kHz) audiometry, extended high-frequency (EHF = 9.0-16.0 kHz) audiometry, distortion product otoacoustic emission (DPOAE) testing, and speech-in-noise (SIN) assessments were prospectively and longitudinally conducted on 74 children with a median of 2 post-PRT evaluations (range, 1-5) per patient. The median age at PRT initiation was 10 years, and median follow-up time was 2 years. Ototoxicity was classified using the Chang Ototoxicity Grading Scale (Chang & Chinosornvatana, 2010) and the American Speech-Language-Hearing Association (ASHA) criteria (ASHA, 1994). Comparisons were made between baseline and most recent DPOAE levels, with evidence of ototoxicity based on criterion reductions of ≥ 6 dB. The critical difference values for comparing SIN scores between two conditions (i.e., pre- and post-PRT) were used to determine a significant change between test scores., Results: At last evaluation, no patients had SNHL in the CF range, and 2 patients had SNHL (Chang Grade 1a) in the EHF range. Based on the ASHA criteria, a decrease in hearing was observed in 0 patients in the CF range alone, in 9 patients in the EHF range alone, and in 15 patients in both the CF and EHF ranges. DPOAE levels decreased at a faster rate at higher versus lower frequencies. For 41 evaluable patients, SIN perception did not decline over time (p = .6463)., Conclusion: At a median follow-up time of 2 years post-PRT, normal hearing was maintained within the CF range. However, subclinical decreases in hearing were observed, particularly in the EHF range and in the DPOAE level; thus, long-term follow-up is recommended to monitor for potential auditory late effects from PRT.

Human hearing sensitivity is easily compromised with overexposure to excessively loud sounds, leading to permanent hearing damage. Consequently, finding activities and/or experiential factors that distinguish "tender" from "tough" ears (i.e., acoustic vulnerability) would be important for identifying people at higher risk for hearing damage. To regulate sound transmission and protect the inner ear against acoustic trauma, the auditory system modulates gain control to the cochlea via biological feedback of the medial olivocochlear (MOC) efferents, a neuronal pathway linking the lower brainstem and cochlear outer hair cells. We hypothesized that a salient form of auditory experience shown to have pervasive neuroplastic benefits, namely musical training, might act to fortify hearing through tonic engagement of these reflexive pathways. By measuring MOC efferent feedback via otoacoustic emissions (cochlear emitted sounds), we show that dynamic ipsilateral and contralateral cochlear gain control is enhanced in musically-trained individuals. Across all participants, MOC strength was correlated with the years of listeners' training suggested that efferent gain control is experience dependent. Our data provide new evidence that intensive listening experience(s) (e.g., musicianship) can strengthen the ipsi/contralateral MOC efferent system and sound regulation to the inner ear. Implications for reducing acoustic vulnerability to damaging sounds are discussed., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Auditory filter theory posits a tradeoff in time-frequency analysis: high temporal precision is achievable only at the expense of poorer frequency resolution and vice versa. Here, we examined the hierarchy of brain mechanisms of these spectrotemporal tradeoffs through a series of physiological and behavioral measures aimed to tap temporal and spectral acuity at different levels of the auditory neuroaxis (cochlea→brainstem→percept). Cochlear and behavioral frequency selectivity was measured by stimulus-frequency otoacoustic emissions (SFOAE) and psychophysical tuning curves; temporal acuity was measured physiologically and behaviorally by paired click recovery of auditory brainstem responses (ABRs) and gap detection thresholds (GDTs), respectively. Comparison of physiological and behavioral estimates of temporal acuity and frequency tuning showed high consistency between measurement domains with temporal thresholds of ∼3-4 ms and filter tuning Q3≈10 across brain and behavioral measures. Cochlear SFOAE estimates of tuning inversely predicted listeners' temporal acuity estimated from both brainstem ABRs and behavioral GDTs. The high predictive power of cochlear responses on temporal thresholds and similarity between time-frequency tradeoffs measured at progressively higher levels of the processing hierarchy (brainstem, behavior) suggest that the temporal resolution of human hearing established in the cochlea might be inherited at progressively higher levels of the hearing pathway.

The mammalian cochlea functions as a filter bank that performs a spectral, Fourier-like decomposition on the acoustic signal. While tuning can be compromised (e.g., broadened with hearing impairment), whether or not human cochlear frequency resolution can be sharpened through experiential factors (e.g., training or learning) has not yet been established. Previous studies have demonstrated sharper psychophysical tuning curves in trained musicians compared to nonmusicians, implying superior peripheral tuning. However, these findings are based on perceptual masking paradigms, and reflect engagement of the entire auditory system rather than cochlear tuning, per se. Here, by directly mapping physiological tuning curves from stimulus frequency otoacoustic emissions (SFOAEs)-cochlear emitted sounds-we show that estimates of human cochlear tuning in a high-frequency cochlear region (4 kHz) is further sharpened (by a factor of 1.5×) in musicians and improves with the number of years of their auditory training. These findings were corroborated by measurements of psychophysical tuning curves (PTCs) derived via simultaneous masking, which similarly showed sharper tuning in musicians. Comparisons between SFOAE and PTCs revealed closer correspondence between physiological and behavioral curves in musicians, indicating that tuning is also more consistent between different levels of auditory processing in trained ears. Our findings demonstrate an experience-dependent enhancement in the resolving power of the cochlear sensory epithelium and the spectral resolution of human hearing and provide a peripheral account for the auditory perceptual benefits observed in musicians. Both local and feedback (e.g., medial olivocochlear efferent) mechanisms are discussed as potential mechanisms for experience-dependent tuning., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Purpose: Patients treated with cranial radiation therapy (RT) are at risk for sensorineural hearing loss (SNHL). Although SNHL is often characterized as a delayed consequence of anticancer therapy, longitudinal reports of SNHL in childhood cancer survivors treated with contemporary RT are limited. We report the incidence, onset, severity, and long-term trajectory of SNHL among children receiving RT. Potential risk factors for SNHL were also identified., Patients and Methods: Serial audiologic testing was conducted on 235 pediatric patients who were treated with conformal or intensity-modulated RT as part of an institutional phase II trial for localized primary brain tumors, including craniopharyngioma, ependymoma, and juvenile pilocytic astrocytoma. All but one patient had measurable cochlear radiation dose (CRD) greater than 0 Gy. The median follow-up from RT initiation to latest audiogram was 9 years with a median of 11 post-RT audiograms per patient. Audiograms were classified by the Chang Ototoxicity Grading Scale. Progression was defined by an increase in Chang grade from SNHL onset to the most recent evaluation., Results: At last evaluation, SNHL was prevalent in 14% of patients: 2.1% had mild and 11.9% had significant SNHL requiring hearing aids. Median time from RT to SNHL onset was 3.6 years (range, 0.4 to 13.2 years). Among 29 patients with follow-up evaluations after SNHL onset, 65.5% experienced continued decline in hearing sensitivity in either ear and 34.5% had no change. Younger age at RT initiation (hazard ratio [HR], 2.32; 95% CI, 1.21 to 4.46), higher CRD (HR, 1.07; 95% CI, 1.03 to 1.11), and cerebrospinal fluid shunting (HR, 2.02; 95% CI, 1.07 to 3.78) were associated with SNHL., Conclusion: SNHL is a late effect of RT that likely worsens over time. Long-term audiologic follow-up for a minimum of 10 years post-RT is recommended., (© 2016 by American Society of Clinical Oncology.)

Objective: Recently, we developed a metric to objectively detect human auditory evoked potentials based on the mutual information (MI) between neural responses and stimulus spectrograms. Here, the MI algorithm is evaluated further for validity in testing the auditory steady-state response (ASSR), a sustained potential used in objective audiometry., Design: MI was computed between spectrograms of ASSRs and their evoking stimuli to quantify the shared time-frequency information between neuroelectric activity and stimulus acoustics. MI was compared against two traditional ASSR detection metrics: F-test and magnitude-squared coherence (MSC)., Study Sample: Using an empirically derived threshold (⊖MI=1.45), MI was applied as a binary classifier to distinguish actual biological responses recorded in human participants (n=11) from sham recordings, containing only EEG noise (i.e., non-stimulus-control condition)., Results: MI achieved high overall accuracy (>90%) in identifying true ASSRs from sham recordings, with true positive/true negative rates of 82/100%. During online averaging, comparison with two other indices (F-test, MSC) indicated that MI could detect ASSRs in roughly half the number of trials (i.e., ∼400 sweeps) as the MSC and performed comparably to the F-test, but showed slightly better signal detection performance., Conclusions: MI provides an alternative, more flexible metric for efficient and automated ASSR detection.

The mammalian cochlea receives feedback from the brainstem medial olivocochlear (MOC) efferents, whose putative 'antimasking' function is to adjust cochlear amplification and enhance peripheral signal detection in adverse listening environments. Human studies have been inconsistent in demonstrating a clear connection between this corticofugal system and behavioral speech-in-noise (SIN) listening skills. To elucidate the role of brainstem efferent activity in SIN perception, we measured ear-specific contralateral suppression of transient-evoked otoacoustic emissions (OAEs), a proxy measure of MOC activation linked to auditory learning in noisy environments. We show that suppression of cochlear emissions is stronger with a more basal cochlear bias in the right ear compared with the left ear. Moreover, a strong negative correlation was observed between behavioral SIN performance and right-ear OAE suppression magnitudes, such that lower speech reception thresholds in noise were predicted by larger amounts of MOC-related activity. This brain-behavioral relation was not observed for left ear SIN perception. The rightward bias in contralateral MOC suppression of OAEs, coupled with the stronger association between physiological and perceptual measures, is consistent with left-hemisphere cerebral dominance for speech-language processing. We posit that corticofugal feedback from the left cerebral cortex through descending MOC projections sensitizes the right cochlea to signal-in-noise detection, facilitating figure-ground contrast and improving degraded speech analysis. Our findings demonstrate that SIN listening is at least partly driven by subcortical brain mechanisms; primitive stages of cochlear processing and brainstem MOC modulation of (right) inner ear mechanics play a critical role in dictating SIN understanding.

Background: Basilar membrane input/output (I/O) functions in mammalian animal models are characterized by linear and compressed segments when measured near the location corresponding to the characteristic frequency. A method of studying basilar membrane compression indirectly in humans involves measuring distortion-product otoacoustic emission (DPOAE) I/O functions. Previous research has linked compression estimates from behavioral growth-of-masking functions to hearing thresholds., Purpose: The aim of this study was to compare compression estimates from DPOAE I/O functions and hearing thresholds at 1 and 2 kHz., Research Design: A prospective correlational research design was performed. The relationship between DPOAE I/O function compression estimates and hearing thresholds was evaluated with Pearson product-moment correlations., Study Sample: Normal-hearing adults (n = 16) aged 22-42 yr were recruited., Data Collection and Analysis: DPOAE I/O functions (L₂ = 45-70 dB SPL) and two-interval forced-choice hearing thresholds were measured in normal-hearing adults. A three-segment linear regression model applied to DPOAE I/O functions supplied estimates of compression thresholds, defined as breakpoints between linear and compressed segments and the slopes of the compressed segments. Pearson product-moment correlations between DPOAE compression estimates and hearing thresholds were evaluated., Results: A high correlation between DPOAE compression thresholds and hearing thresholds was observed at 2 kHz, but not at 1 kHz. Compression slopes also correlated highly with hearing thresholds only at 2 kHz., Conclusions: The derivation of cochlear compression estimates from DPOAE I/O functions provides a means to characterize basilar membrane mechanics in humans and elucidates the role of compression in tone detection in the 1-2 kHz frequency range., (American Academy of Audiology.)

Background: Platinum-based chemotherapy and cranial radiation are effective treatment options commonly prescribed for a variety of childhood cancers. These therapies can, and often do, result in early- and late-onset adverse health effects such as hearing loss. Undetected hearing loss is particularly concerning in young children developing speech and language skills and can negatively affect academic achievement and the psychosocial well-being of both young and older children. Early detection of hearing loss in pediatric oncology patients and early intervention are critical to help these patients succeed in achieving these developmental milestones., Purpose: The primary goal of this study was to create a tutorial for audiologists concerning the monitoring of ototoxicity in the pediatric oncology population. Monitoring hearing for children receiving potentially ototoxic cancer treatments presents special issues and challenges for audiologists. This tutorial will orient the reader to these special issues and challenges, and potential solutions will be proposed., Design: This tutorial is organized into sections, including an overview of platinum compound and cranial radiation treatments commonly used to treat pediatric cancer, modifications of the test battery required to appropriately monitor for ototoxic hearing loss in children, a proposal for a monitoring protocol, and descriptions of the grading scales that are frequently used by oncologists to determine the severity of ototoxic hearing loss., Conclusions: Identification of ototoxicity is crucial in children receiving cancer treatments because of the impact that acquired hearing loss has on social and educational outcomes in the developing child. Monitoring hearing in children presents challenges that are unique to this population. Much effort has been put forth in developing and validating the International Society of Pediatric Oncology ototoxicity grading scale for international use in reporting auditory outcomes in clinical trials. In the future, the development of standardized monitoring protocols will assist audiologists in providing optimal care to children treated for cancer., (American Academy of Audiology.)

Musicianship confers enhancements to hearing at nearly all levels of the auditory system from periphery to percept. Musicians' superior psychophysical abilities are particularly evident in spectral discrimination and noise-degraded listening tasks, achieving higher perceptual sensitivity than their nonmusician peers. Greater spectral acuity implies that musicianship may increase auditory filter selectivity. This hypothesis was directly tested by measuring both forward- and simultaneous-masked psychophysical tuning curves. Sharper filter tuning (i.e., higher Q10) was observed in musicians compared to nonmusicians. Findings suggest musicians' pervasive listening benefits may be facilitated, in part, by superior spectral processing/decomposition as early as the auditory periphery.

Background: Reporting ototoxicity is frequently complicated by use of various ototoxicity criteria. The International Society of Pediatric Oncology (SIOP) ototoxicity grading scale was recently proposed for standardized use in reporting hearing loss outcomes across institutions. The aim of this study was to evaluate the concordance between the Chang and SIOP ototoxicity grading scales. Differences between the two scales were identified and the implications these differences may have in the clinical setting were discussed., Procedures: Audiological evaluations were reviewed for 379 patients with newly diagnosed medulloblastoma (ages 3-21 years). Each patient was enrolled on one of two St. Jude clinical protocols that included craniospinal radiation therapy and four courses of 75 mg/m(2) cisplatin chemotherapy. The latest audiogram conducted 5.5-24.5 months post-protocol treatment initiation was graded using the Chang and SIOP ototoxicity criteria. Clinically significant hearing loss was defined as Chang grade ≥2a and SIOP ≥2. Hearing loss was considered serious (requiring a hearing aid) at the level of Chang grade ≥2b and SIOP ≥3., Results: A strong concordance was observed between the Chang and SIOP ototoxicity scales (Stuart's tau-c statistic = 0.89, 95% CI: 0.86, 0.91). Among those patients diagnosed with serious hearing loss, the two scales were in good agreement. However, the scales deviated from one another in classifying patients with less serious or no hearing loss., Conclusions: Although discrepancies between the Chang and SIOP ototoxicity scales exist primarily for patients with no or minimal hearing loss, the scales share a strong concordance overall., (© 2013 Wiley Periodicals, Inc.)

The existence of efferent feedback from cortical and subcortical brain centers to the hair cells of the cochlea has been recognized for many years, but the role that efferent neurons play in hearing is not completely known. Stimulation of medial olivocochlear (MOC) efferent neurons suppresses sound-evoked basilar membrane responses and changes the tuning of single auditory nerve fibers in animal models. Both of these effects are linked to a MOC-induced reduction in the gain of the cochlear amplification provided by outer hair cells. To non-invasively examine the link between cochlear suppression and tuning in humans, stimulus-frequency otoacoustic emissions (SFOAEs) were recorded in conditions with and without contralateral acoustic stimulation (CAS) from 28 normal-hearing participants. SFOAEs were measured using clusters of closely-spaced probe-tone frequencies centered near 1.4 and 2.0kHz. An index of cochlear tuning, QERB, was calculated based on measures of SFOAE group delay at both 1.4 and 2.0kHz. A statistically significant (p<0.01) decrease in SFOAE levels acquired during CAS was detected only for the SFOAE cluster centered at 2kHz. No statistically significant differences in QERB were found between conditions with and without CAS at 1.4 and 2.0kHz. These findings suggest that in humans, tuning based on SFOAE group delay estimates is not appreciably altered at cochlear locations with MOC efferent-induced reductions in cochlear gain., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Several lines of evidence suggest that medial olivocochlear (MOC) efferent neurons modify cochlear output to improve signal detection in noise. In animal models, stimulation of MOC efferents reduces the amount of compression in basilar membrane (BM) growth functions. Linearization of BM growth functions may assist in extending the neural response to the signal above that of noise, leading to a decrease in masking. In order to test this hypothesis, effects of MOC efferent neurons on BM compression were studied indirectly in humans by examining the effects of contralateral noise on distortion-product otoacoustic emission (DPOAE) input-output functions at 1.0 and 2.0kHz. Compression threshold estimates from a three-segment linear regression model applied to the DPOAE functions were derived in order to determine correlations with psychophysical measurements of masking of tones at 1.0 and 2.0kHz. Contralateral noise shifted the DPOAE compression threshold to a significantly higher level at 1.0kHz, but not at 2.0kHz. A significant negative correlation between the change in DPOAE compression threshold and the amount of masking at 1.0kHz was observed, but no correlation between these variables was detected at 2.0kHz. The results of this experiment at the lower test frequency indicated that contralateral noise linearized DPOAE input-output functions, and individuals with larger DPOAE compression threshold shifts tended to exhibit less masking. Under certain conditions, decreases in cochlear compression induced by MOC efferent neurons may lead to unmasking of tones presented in noise., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

Objective: Carboplatin is a common chemotherapy agent with potential ototoxic side effects that is used to treat a variety of pediatric cancers, including retinoblastoma. Retinoblastoma is a malignant tumor of the retina that is usually diagnosed in young children. Distortion-product otoacoustic emission tests offer an effective method of monitoring for ototoxicity in young children. This study was designed to compare measurements of distortion-product otoacoustic emissions obtained before and after several courses of carboplatin chemotherapy in order to examine if (a) mean distortion-product otoacoustic emission levels were significantly different; and (b) if criterion reductions in distortion-product otoacoustic emission levels were observed in individual children., Methods: A prospective repeated measures study. Ten children with a median age of 7.6 months (range, 3-72 months) diagnosed with unilateral or bilateral retinoblastoma were examined. Distortion-product otoacoustic emissions were acquired from both ears of the children with 65/55 dB SPL primary tones (f(2)=793-7996 Hz) and a frequency resolution of 3 points/octave. Distortion-product otoacoustic emission levels in dB SPL were measured before chemotherapy treatment (baseline measurement) and after 3-4 courses of chemotherapy (interim measurement). Comparisons were made between baseline and interim distortion-product otoacoustic emission levels (collapsed across ears). Evidence of ototoxicity was based on criterion reductions (≥ 6 dB) in distortion-product otoacoustic emission levels., Results: Significant differences between baseline and interim mean distortion-product otoacoustic emission levels were only observed at f(2) = 7996 Hz. Four children exhibited criterion reductions in distortion-product otoacoustic emission levels., Conclusions: Mean distortion-product otoacoustic emission levels at most frequencies were not changed following 3-4 courses of carboplatin chemotherapy in children with retinoblastoma. However, on an individual basis, children receiving higher doses of carboplatin exhibited criterion reductions in distortion-product otoacoustic emission level at several frequencies. These findings suggest that higher doses of carboplatin affect outer hair cell function, and distortion-product otoacoustic emission tests can provide useful information when monitoring children at risk of developing carboplatin ototoxicity., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

The purpose of this study was to examine if a pre-determined exposure level and duration of MP3 player music would result in significant changes in cochlear function when measured with audiometric and physiological methods. Distortion-product otoacoustic emissions (DPOAEs), synchronized spontaneous otoacoustic emissions (SSOAEs), and hearing thresholds were measured in 20 normal-hearing adults before and after a 30-minute MP3 player music exposure. DPOAEs were acquired with 65/45 dB SPL primary tones (f(2)=0.842-7.996 kHz) with a frequency resolution of 8 points/octave. A probe microphone system recorded ear-canal music levels and was used to equalize levels at approximately 85 dBC across individuals during the music presentation. Comparison of pre- and post-exposure measurements revealed no significant differences in hearing thresholds, but DPOAE levels in half-octave bands centered from 1.4-6.0 kHz were significantly reduced following the music exposure. Post-exposure shifts in SSOAE frequency and level were highly variable in individuals identified with SSOAEs. The results for the exposure conditions explored in this study indicate that changes in otoacoustic emissions may precede the development of music-induced hearing threshold shifts.

This study investigated the effects of irrelevant sounds on the serial recall performance of visually presented digits in a sample of children diagnosed with (central) auditory processing disorders [(C)APD] and age- and span-matched control groups. The irrelevant sounds used were samples of tones and speech. Memory performance was significantly disrupted in the presence of irrelevant sounds in all three groups of children. While irrelevant speech was more disruptive than irrelevant tones in the two control groups, children diagnosed with (C)APD did not show larger disruption from irrelevant speech compared to irrelevant tones. Children diagnosed with (C)APD appear to process speech differently from their typically developing peers, and this may be remediated with auditory training procedures and the placement of these children in smaller classes.

The purpose of this investigation was to compare the effects of monaural and binaural stimulation on unilaterally-measured vestibular evoked myogenic potential (VEMP) magnitude and latency. The subjects were eighteen normal-hearing adults with no history of vestibular disease. Monaural VEMPs were acquired with air-conducted (AC) and bone-conducted (BC) 500 Hz tone bursts presented at 95 dB nHL and 70 dB nHL, respectively. These stimuli were simultaneously paired with 95 dB nHL contralateral tone bursts at 250, 500, 750, or 1000 Hz during acquisition of binaural VEMPs. Results indicated that AC-VEMP relative magnitudes decreased in each of the binaural conditions compared to the monaural condition. However, no changes in relative magnitude between conditions occurred for BC-VEMPs. Similar latencies were observed for monaural and binaural VEMPs. Differences in bilateral interaction seen between the AC-VEMP and BC-VEMP conditions are consistent with modification of sound transmission through the ear during presentations of binaural sound.

During the simultaneous monaural presentation of two primary tones, distortion products can be measured acoustically in the ear canal (DPOAEs) and electrically as auditory evoked potentials (DPAEPs). The purpose of this investigation was to elucidate the sources of nonlinearity within the human auditory system responsible for generating quadratic (QDT) and cubic (CDT) difference tones. Measurements of DPOAEs and DPAEPs were obtained from 24 normal-hearing adults (12 male) in conditions with and without presentation of a 60 dB SPL contralateral noise. The effects of primary-tone signal duration and mode of presentation on measurements of DPAEPs were also examined. Results indicated that overall, both acoustic and electric distortion products were suppressed during presentation of a contralateral noise. Increases in the duration of the primary tones caused increases in DPAEP amplitudes. A greater proportion of individuals exhibited DPAEPs with monotic compared to dichotic presentation of the primary tones. The findings of the investigation supported the conjecture that a cochlear nonlinearity produced CDT acoustic and electric distortion products. Evidence concerning the origin of the QDT DPAEP was inconclusive, and contributions from both cochlear and neural nonlinear sources could not be ruled out.