Semi-implantable transcutaneous bone conduction hearing devices

The aim of this study was to evaluate the performance and limits of an adhesive bone conduction hearing aid in patients implanted with an active transcutaneous bone conduction implant. Therefore, hearing performance and subjective benefit of patients with mixed and conductive hearing loss were assessed with both bone conduction devices. This cohort study was conducted at a tertiary care center. Fifteen subjects, who had been implanted with an active transcutaneous device previously, were included and used the adhesive hearing device for 3 weeks instead of the implant. Subjects underwent two sets of audiological tests as well as assessments of quality of life at the beginning and at the end of the testing period. Audiological results showed a significantly greater improvement in regards to functional hearing gain and word recognition scores with the transcutaneous bone conduction device than the nonimplantable adhesive device. Regression analysis showed a trend toward greater improvement with the transcutaneous device compared with the adhesive device in patients with an increasing bone conduction threshold. Hearing-specific and general quality-of-life questionnaires revealed no significant difference between the two devices. Patients with mixed or conductive hearing loss experience hearing gain with both, the adhesive device and the active transcutaneous device. The adhesive device may be a valuable alternative to the active transcutaneous device, depending on the individual bone conduction threshold.

Objective: To develop an algorithm that prescribes targets for bone conduction frequency response shape, compression, and output limiting, along with a clinical method that ensures accurate transforms between assessment and verification stages of the clinical workflow. Design: Technical report of target generation and validation. Study sample: We recruited 39 adult users of unilateral percutaneous bone conduction hearing aids with a range of unilateral, bilateral, mixed and conductive hearing losses across the sample. Results: The initial algorithm over-prescribed output compared to the user’s own settings in the low frequencies, but provided a good match to user settings in the high frequencies. Corrections to the targets were derived and implemented as a low-frequency cut aimed at improving acceptance of the wearer’s own voice during device use. Conclusions: The DSL-BCD prescriptive algorithm is compatible with verification of devices and fine-tuning to target for percutaneous bone conduction hearing devices that can be coupled to a skull simulator. Further study is needed to investigate the appropriateness of this prescriptive algorithm for other input levels, and for other clinical populations including those with single-sided deafness, bilateral devices, children and users of transcutaneous bone conduction hearing aids.

Patients with air-bone-gaps that cannot be corrected successfully by tympanoplasty or with mixed hearing loss may be treated with bone conducting hearing aids. Their disadvantages are the obvious external fixation components or the biological and psychosocial problems of open implants. We have developed a new partially implantable Bone Conduction Hearing Device (BCHD) without a percutaneous abutment and have been using them clinically for over 6 years. The principle of these BCHD is a magnetic coupling and acoustic transmission between implanted and external magnets. The goal of this study was to evaluate its clinical and audiologic results in patients with unilateral or bilateral congenital aural atresia. Magnets are implanted into shallow bone beds in a 1-step procedure. The skin above the magnets is slightly thinned. The external device fixed with counter magnets in a base plate. Twenty-one patients who have been implanted due to congenital atresia showed up for this follow-up study. The follow-up period was 19.3 ± 12.2 months, with a range of 0.2 to 46.6 months. The average age of the patients at the time of implantation was 12.4 years with a wide range from 6.0 to 50.0 years. The average hearing gain was 31 ± 8 dB, and the suprathreshold word recognition tests increased by 57% ± 23%. Strength of the magnetic force that the patients had chosen themselves measured 0.9 ± 0.4 N with a range from 0.3 to 1.8 N. Skin thickness over the implants measured sonographically was 3.9 ± 0.8 mm (range, 2.5-5.6 mm). This new bone conducting hearing device only needs one operation, has a very low risk for complication, and a hearing gain similar to other bone conducting hearing aids. We have found high comfort and safety of this system and conclude that it could be a valuable alternative to other conventional or percutaneous bone conducting hearing solutions.

The present study evaluated early auditory localization abilities of cochlear implant (CI) recipients with normal or near-normal hearing (NH) in the contralateral ear. The goal of the study was to better understand the effect of CI listening experience on localization in this population. Twenty participants with unilateral hearing loss enrolled in a prospective clinical trial assessing outcomes of cochlear implantation (ClinicalTrials.gov Identifier: NCT02203305). All participants received the MED-EL Standard electrode array, were fit with an ear-level audio processor, and listened with the FS4 coding strategy. Localization was assessed in the sound field using an 11-speaker array with speakers uniformly positioned on a horizontal, semicircular frame. Stimuli were 200-msec speech-shaped noise bursts. The intensity level (52, 62, and 72 dB SPL) and sound source were randomly interleaved across trials. Participants were tested preoperatively, and 1, 3, and 6 months after activation of the audio processor. Performance was evaluated in two conditions at each interval: (1) unaided (NH ear alone [NH-alone] condition), and (2) aided, with either a bone conduction hearing aid (preoperative interval; bone conduction hearing aid + NH condition) or a CI (postoperative intervals; CI + NH condition). Performance was evaluated by comparing root-mean-squared (RMS) error between listening conditions and between measurement intervals. Mean RMS error for the soft, medium, and loud levels were 66°, 64°, and 69° in the NH-alone condition and 72°, 66°, and 70° in the bone conduction hearing aid + NH condition. Participants experienced a significant improvement in localization in the CI + NH condition at the 1-month interval (38°, 35°, and 38°) as compared with the preoperative NH-alone condition. Localization in the CI + NH condition continued to improve through the 6-month interval. Mean RMS errors were 28°, 25°, and 28° in the CI + NH condition at the 6-month interval. Adult CI recipients with normal or near-normal hearing in the contralateral ear experienced significant improvement in localization after 1 month of device use, and continued to improve through the 6-month interval. The present results show that binaural acclimatization in CI users with unilateral hearing loss can progress rapidly, with marked improvements in performance observed after only 1 month of listening experience.

Children with permanent unilateral hearing loss (UHL) are an understudied population, with limited data to inform the guidelines on clinical management. There is a funding gap in healthcare provision for the children with UHL in the United Kingdom, where genetic screening, support services, and devices are not consistently provided or fully funded in all areas. They are a disparate population with regard to aetiology and their degree of hearing loss, and hence their device choice and use. Despite having one "good ear", some children with UHL can have similar outcomes, socially, behaviourally, and academically, to children with bilateral hearing loss, highlighting the importance of understanding this population. In this longitudinal cohort study, we aimed to characterise the management of the children with UHL and the gaps in the support services that are provided for the children in Nottingham, United Kingdom. A cohort study was conducted collecting longitudinal data over 17 years (2002-2019) for 63 children with permanent congenital confirmed UHL in a large tertiary regional referral centre for hearing loss in Nottingham, United Kingdom. The cases of UHL include permanent congenital, conductive, mixed, or sensorineural hearing loss, and the degree of hearing loss ranges from mild to profound. The data were taken from their diagnostic auditory brainstem responses and their two most recent hearing assessments. Descriptors were recorded of the devices trialled and used and the diagnoses including aetiology of UHL, age of first fit, degree of hearing loss, when and which type of device was used, why a device was not used, the support services provided, concerns raised, and who raised them. Most children (45/63; 71%) trialled a device, and the remaining 18 children had no device trial on record. Most children (20/45; 44%) trialled a bone-conduction device, followed by contralateral routing of signal aid (15/45; 33%) and conventional hearing aids (9/45; 20%). Most children (36/45; 80%) who had a device indicated that they wore their device "all day" or every day in school. Few children (8/45; 18%) reported that they wore their device rarely, and the reasons for this included bullying (3/8), feedback from the device (2/8), and discomfort from the device (2/8). Only one child reported that the device was not helping with their hearing. The age that the children were first fitted with their hearing device varied a median of 2.5 years for hearing aids and bone-conduction devices and 7 years for a contralateral routing of signal aid. The length of time that the children had the device also varied widely (median of 26 months, range 3-135 months); the children had their bone-conduction hearing aid for the longest period of time (median of 32.5 months). There was a significant trend where more recent device fittings were happening for children at a younger age. Fifty-one children were referred by the paediatric audiologist to a support service, 72.5% (37/51) were subsequently followed up by the referred service with no issue, whilst the remaining 27.5% (14/51) encountered an issue leading to an unsuccessful provision of support. Overall, most children (65%, 41/63) had no reported concerns, and 28.5% (18/63) of the children went on to have a documented concern at some point during their audiological care: five with hearing aid difficulties, five with speech issues, four with no improvement in hearing, three facing self-image or bullying issues, and one case of a child struggling to interact socially with friends. Three of these children had not trialled a device. We documented every concern reported from the parents, clinicians, teachers of the deaf, and from the children themselves. Where concerns were raised, more than half (58.6%, 10/18) were by schools and teachers, the remaining four concerns were raised by the family, and further four concerns were raised by the children themselves. To discover what management will most benefit which children with permanent UHL, we first must characterise their treatment, their concerns, and the support services available for them. Despite the children with UHL being a highly disparate population-in terms of their aetiology, their device use, the degree of hearing loss, and the age at which they trial a device-the majority report they use their device mostly in school. In lieu of available data and in consideration of the devices that are available to them, it could be useful to support families and clinicians in understanding the devices which are most used and where they are used. Considering the reasons for cessation of regular device use counselling and support services would be vital to support the children with UHL.

A new intraoral bone-conduction device has advantages over existing bone-conduction devices for reducing the auditory deficits associated with single-sided deafness (SSD). Existing bone-conduction devices effectively mitigate auditory deficits from single-sided deafness but have suboptimal microphone locations, limited frequency range, and/or require invasive surgery. A new device has been designed to improve microphone placement (in the ear canal of the deaf ear), provide a wider frequency range, and eliminate surgery by delivering bone-conduction signals to the teeth via a removable oral appliance. Forces applied by the oral appliance were compared with forces typically experienced by the teeth from normal functions such as mastication or from other appliances. Tooth surface changes were measured on extracted teeth, and transducer temperature was measured under typical use conditions. Dynamic operating range, including gain, bandwidth, and maximum output limits, were determined from uncomfortable loudness levels and vibrotactile thresholds, and speech recognition scores were measured using normal-hearing subjects. Auditory performance in noise (Hearing in Noise Test) was measured in a limited sample of SSD subjects. Overall comfort, ease of insertion, and removal and visibility of the oral appliance in comparison with traditional hearing aids were measured using a rating scale. The oral appliance produces forces that are far below those experienced by the teeth from normal functions or conventional dental appliances. The bone-conduction signal level can be adjusted to prevent tactile perception yet provide sufficient gain and output at frequencies from 250 to 12,000 Hz. The device does not damage tooth surfaces nor produce heat, can be inserted and removed easily, and is as comfortable to wear as traditional hearing aids. The new microphone location has advantages for reducing the auditory deficits caused by SSD, including the potential to provide spatial cues introduced by reflections from the pinna, compared with microphone locations for existing devices. A new approach for SSD has been proposed that optimizes microphone location and delivers sound by bone conduction through a removable oral appliance. Measures in the laboratory using normal-hearing subjects indicate that the device provides useful gain and output for SSD patients, is comfortable, does not seem to have detrimental effects on oral function or oral health, and has several advantages over existing devices. Specifically, microphone placement is optimized for reducing the auditory deficit caused by SSD, frequency bandwidth is much greater, and the system does not require surgical placement. Auditory performance in a small sample of SSD subjects indicated a substantial advantage compared with not wearing the device. Future studies will involve performance measures on SSD patients wearing the device for longer periods.

Surgical Considerations for an Osseointegrated Steady State Implant (OSIA2®) in Children.

There is a lack of high level of evidence studies comparing the effect of different treatment options for single-sided deafness (SSD). To determine the effect of a cochlear implant (CI), bone conduction device (BCD), contralateral routing of signals hearing aid (CROS), and no treatment on speech perception in noise outcomes in patients with SSD. In this single-center randomized clinical trial, adult patients with SSD were randomized into 3 groups: CI; a trial period with first a BCD on a headband and then a CROS; or a trial period with first a CROS and then a BCD on a headband. After the trial periods, patients opted for a BCD, CROS, or no treatment. Measurements were completed at baseline and at 3, 6, 12, and 24 months of follow-up. Data were collected from July 2014 to October 2021, and data were analyzed from December 2022 to May 2023. CI, BCD then CROS, or CROS then BCD. The primary outcome was the speech reception threshold in noise (SRTn), measured with speech and noise from the front (S0N0), speech directed to the poor ear and noise to the better ear (SpeNbe), and vice versa (SbeNpe). The secondary outcome was disease-specific quality of life (QOL). Of 120 included patients, 60 (50.0%) were female, and the mean (SD) age at inclusion was 53.0 (12.1) years. At the start of follow-up, 28 patients received a CI, 25 a BCD, 34 a CROS, and 26 chose no treatment. At 24 months, the CI group had significantly better speech perception in noise scores than the BCD group (difference in SRTn: SbeNpe, -4.7 dB; 95% confidence interval, -6.6 to -3.0; SpeNbe, -2.2 dB; 95% confidence interval, -4.6 to -1.1), the CROS group (difference in SRTn: S0N0, -1.3 dB; 95% confidence interval, -1.7 to -0.2; SbeNpe, -5.3 dB; 95% confidence interval, -6.0 to -3.1), and the no treatment group (difference in SRTn: SpeNbe, -6.3 dB; 95% confidence interval, -7.5 to -4.9). Compared with the no treatment group, the BCD and CROS groups showed significantly better (difference in SRTn for SpeNbe, -4.1 dB [95% confidence interval, -5.2 to -1.5] and -4.1 dB [95% confidence interval, -6.1 to -3.3], respectively) or worse (difference for SbeNpe, 4.0 dB [95% confidence interval, 2.6 to 6.2] and 4.6 dB [95% confidence interval, 2.8 to 5.7], respectively) speech perception in noise. Self-reported speech perception abilities were significantly better for the CI group compared with the BCD, CROS, and no treatment groups. In this randomized clinical trial, the CI group outperformed the BCD, CROS, and no treatment groups in terms of speech perception in noise and disease-specific QOL in patients with SSD after 24 months of follow-up. These results indicate that patients with SSD can partially regain the advantages of binaural hearing after treatment. trialregister.nl Identifier: NL4457.

SUMMARYObjectiveTo assess the hearing benefit with a unilateral bone conduction hearing aid in a cohort of children with unilateral aural atresia.MethodsCross-sectional case series pilot study involving 7 children (median age: 10 years, range 6-11). All patients underwent pure-tone, speech, aided sound field and aided speech audiometry and Simplified Italian Matrix Test (SIMT) with and without bone conduction hearing aid (Baha 5® CochlearTM). Cognitive abilities were assessed in 5 patients.ResultsThe mean air conduction pure-tone average (PTA) of the atretic ear was 63.2 ± 6.9 dB, while the bone conduction PTA was 12.6 ± 4.7 dB. Speech discrimination score of the atretic ear was 88.6 ± 3.8 dB, while with the hearing aid it was 52.8 ± 1.9 dB. In the contralateral ear, there was no significant air-bone gap, and PTAs for air and bone conduction thresholds were within normal range (PTA ≤ 25 dB). The mean aided air conduction hearing threshold was 26.2 ± 7.97. Mean speech recognition threshold without the hearing aid was -5.1 ± 1.9 dB, and -6.0 ± 1.7 dB with the hearing aid tested with the SIMT. The mean score of the cognitive test was 46.8 ± 42.8.ConclusionsThese preliminary findings should encourage clinicians in proposing a unilateral bone conduction hearing aid in children with unilateral atresia.

The purpose of this study is to evaluate binaural hearing ability in adults with normal hearing when bone conduction (BC) stimulation is bilaterally applied at the bone conduction hearing aid (BCHA) implant position as well as at the audiometric position on the mastoid. The results with BC stimulation are compared with bilateral air conduction (AC) stimulation through earphones. Binaural hearing ability is investigated with tests of spatial release from masking and binaural intelligibility level difference using sentence material, binaural masking level difference with tonal chirp stimulation, and precedence effect using noise stimulus. In all tests, results with bilateral BC stimulation at the BCHA position illustrate an ability to extract binaural cues similar to BC stimulation at the mastoid position. The binaural benefit is overall greater with AC stimulation than BC stimulation at both positions. The binaural benefit for BC stimulation at the mastoid and BCHA position is approximately half in terms of decibels compared with AC stimulation in the speech based tests (spatial release from masking and binaural intelligibility level difference). For binaural masking level difference, the binaural benefit for the two BC positions with chirp signal phase inversion is approximately twice the benefit with inverted phase of the noise. The precedence effect results with BC stimulation at the mastoid and BCHA position are similar for low frequency noise stimulation but differ with high-frequency noise stimulation. The results confirm that binaural hearing processing with bilateral BC stimulation at the mastoid position is also present at the BCHA implant position. This indicates the ability for binaural hearing in patients with good cochlear function when using bilateral BCHAs.

ObjectivesExperimental investigation of the contribution of the middle ear to bone conduction (BC) hearing sensation. MethodsExperiments were conducted on 6 fresh cadaver whole head specimens. The electromagnetic actuators from a commercial bone conduction hearing aid (BCHA), Baha® 5 SuperPower and BoneBridge (BB), were used to provide stepped sine stimulus in the range of 0.1–10 kHz. The middle ear transfer function (METF) of each cadaver head was checked against the ASTM F2504-05 standard. In a first step, the stapes stimulus into the cochlea, under BC, was estimated based on the differential velocity between the stapes footplate and the promontory. This was based on sequential measurements of the 3D velocity of the stapes footplate and the promontory. In parallel, the differential tympanic membrane (TM) pressure was recorded by measuring sound pressure in the middle ear and in the external auditory canal each measured 1–2 mm from the TM. The measurement procedure was then sequentially repeated, after: a) opening the middle ear cavity; b) ISJ interruption; c) closing the middle ear cavity. At the end, the velocity at each actuator is measured for comparison purposes. Stapes footplate and promontory motion was quantified as the 3D motion at a single measurement point via a three-dimensional laser Doppler vibrometer (3D LDV) system. The combined motion was used for all motion parameters. ResultsThe METF, based on the combined motion, matches better to the ASTM standard, making the measurements resilient to oblique measurement directions. The Baha actuator produced ∼10 dB SPL more output than the BB above 2 kHz. This resulted in 2–5 dB increase in the differential pressure across the TM, after middle ear cavity opening, for Baha stimulation, and up to 9 dB drop (around 2 kHz) for BB stimulation. The differential stapes motion follows linearly the level of motion of the stimulation area, however, it is affected by actuator resonances in a more complex way. Interruption of the ISJ, reduces the differential motion of the stapes with 1–5 dB, only at 1–3 kHz. ConclusionCombined velocity more objectively describes the stapes and skull motion, than any individual motion component. The state of the ME cavity and the ISJ affect the cochlear input of the stapes, however, the effect is limited in frequency and magnitude.

The Bonebridge hearing aid (Med-EL, Innsbruck, Austria) is a semi-implantable hearing system with transcutaneous bone conduction that was implemented in Europe in 2012. It is indicated for patients with conductive and mixed hearing loss or unilateral profound sensorineural hearing loss, who do not obtain adequate benefits with conventional hearing aids and are not candidates for middle ear reconstructive surgery. The Bonebridge device, being an active transcutaneous bone conduction implant, can overcome the disadvantages of percutaneous bone conduction devices. The Vibrant Soundbridge hearing aid (Med-EL, Innsbruck, Austria) was implemented in Europe in 1996 as an implantable hearing device in the middle ear in patients with mild to severe sensorineural, conductive or mixed hearing loss with medical and audiological contraindications for the use of conventional hearing aids or with rapidly progressive sensorineural hearing loss. The Bonebridge and Vibrant Soundbridge devices, used in patients with the same indication criteria, had similar audiological results – adequate hearing rehabilitation with improvement of subjective hearing (perception of silent and noisy speech, spatial hearing, hearing quality, sound localization), a significant increase in perceived quality of life and patients’ satisfaction with the hearing aid (comfort, sound quality, cosmetic appearance). Because the Vibrant Soundbridge device requires the floating mass transducer to be coupled to the ossicles, round window, or oval window, this surgery carries a higher risk of inner ear injury than surgery with the Bonebridge device. The advantages of the Vibrant Soundbridge system, compared to the Bonebridge device, are the potential for greater stimulation power, especially at high frequencies, unilaterally stimulating the affected ear without influencing the contralateral ear through bone conduction.

Single-sided deafness (SSD) is often accompanied by tinnitus, resulting in a decreased quality of life. Currently, there is a lack of high level of evidence studies comparing different treatment options for SSD regarding tinnitus reduction. This randomized controlled trial (RCT) evaluated the effect of a cochlear implant (CI), bone conduction device (BCD), contralateral routing of sound (CROS), and no treatment on tinnitus outcomes in SSD patients, with follow-up extending to 24 months. A total of 120 adult SSD patients were randomized to three groups: CI, a trial period with first a BCD on a headband, then a CROS, or vice versa. After the trial periods, patients opted for a BCD, CROS, or no treatment. At the start of follow-up, 28 patients were implanted with a CI, 25 patients with a BCD, 34 patients had a CROS, and 26 patients chose no treatment. The Tinnitus Handicap Inventory (THI), Tinnitus Questionnaire (TQ), the Visual Analog Scale (VAS), and the Hospital Anxiety and Depression Scale (HADS) were completed at baseline and at 3, 6, 12, and 24 months of follow-up. The CI and BCD groups showed significantly decreased tinnitus impact scores. The CI group showed the largest decrease, which was already observed at 3 months of follow-up. Compared to the baseline, the median THI score decreased by 23 points, the TQ score by 17 points, and the VAS score by 60 points at 24 months. In the BCD group, the TQ score decreased by 9 points, and the VAS decreased by 25 points at 24 months. The HADS anxiety and depression subscale showed no indication for anxiety or depression at baseline, nor at 24 months, for all groups. In this RCT, SSD patients treated with a CI or BCD showed an overall decrease in tinnitus impact scores up to 24 months compared to baseline. The CI group reported a stable and the largest reduction. Cochlear implants appear to be superior to BCD and CROS, and no treatment for achieving partial or complete resolution of tinnitus in patients with SSD. Netherlands Trial Register, www.onderzoekmetmensen.nl/nl/trial/26952, NTR4457, CINGLE trial.

The maximum output provided by a bone conduction (BC) device is one of the main factors that determines the success when treating patients with conductive or mixed hearing loss. Different approaches such as sound pressure measurements using a probe microphone in the external auditory canal or a surface microphone on the forehead have been previously introduced to determine the maximum output of active transcutaneous BC devices that are not directly accessible after implantation. Here, we introduce a method to determine the maximum output hearing level (MOHL) of a transcutaneous active BC device using patients' audiometric data. We determined the maximum output in terms of hearing level MOHL (dB HL) of the Bonebridge using the audiometric and direct BC threshold of the patient together with corresponding force levels at hearing threshold and the maximum force output of the device. Seventy-one patients implanted with the Bonebridge between 2011 and 2020 (average age 45 ± 19 years ranging from 5 to 84 years) were included in this study. The analyses of MOHLs were performed by (1) dividing patients into two groups with better or worse average audiometric BC threshold (0.5, 1, 2, 4 kHz), on the ipsilateral side or (2) by separating the MOHLs based on better or worse frequency-by-frequency specific audiometric BC thresholds on the ipsilateral (implanted) side. When using a frequency-by-frequency analysis obtained average ipsilateral MOHLs were in the range between 51 and 73 dB HL for frequencies from 0.5 to 6 kHz in the group with better audiometric BC threshold on the ipsilateral ears. The average contralateral MOHLs in the group with better contralateral hearing were in the range from 43 to 67 dB HL. The variability of the data was approximately 6 to 11 dB (SDs) across measured frequencies (0.5 to 6 kHz). The average MOHLs were 4 to 8 dB higher across frequencies in the group with better audiometric BC threshold on the ipsilateral ears than in the group with better audiometric BC threshold on the contralateral ears. The differences between groups were significant across measured frequencies ( t test; p < 0.05). Our proposed method demonstrates that the individual frequency-specific MOHL on the ipsilateral and contralateral side of individual patients with a transcutaneous BC device can be determined mainly using direct and audiometric BC threshold data of the patients from clinical routine. The average MOHL of the implant was found 4 to 8 dB higher on the ipsilateral (implanted) side than on the contralateral side.

To improve understanding of normal responses in infants by comparing air conduction (AC) and bone conduction (BC) auditory thresholds using both the auditory steady state response (ASSR) and behavioral testing methods in normal-hearing infants (6 to 18 months of age) and adults. At present, there are no correction factors available for estimating BC behavioral thresholds from BC ASSR thresholds, which is a barrier to clinical implementation of the ASSR. In addition, previous studies have reported infant-adult differences in AC and BC sensitivity, which suggest a "maturational" air-bone gap (ABG) that is not attributable to a conductive pathology; no study has yet compared AC and BC thresholds for either ASSR or behavioral methods in the same individuals. The objectives of the present study are: (1) to compare BC thresholds between methods and provide the initial step toward positing correction factors to predict BC behavioral thresholds, (2) to directly compare AC and BC thresholds to provide an accurate estimate of the maturational ABG, (3) to determine preliminary normal levels for BC and AC ASSRs to exponentially amplitude modulated stimuli, and (4) to investigate infant-adult differences in AC and BC thresholds using ASSRs and behavioral assessment tools. Participants were 23 infants (6.5 to 19.0 months of age) and 12 adults (17 to 50 years of age) with normal hearing. Thresholds were estimated at 500, 1000, 2000, and 4000 Hz using air- and bone-conducted stimuli for ASSRs and behavioral testing. The ASSR stimuli were exponential envelope modulated (amplitude modulation [AM]) at modulation frequencies of 78, 85, 93, and 101 Hz for 500, 1000, 2000, and 4000 Hz, respectively, presented simultaneously. Frequency-modulated (warble tone) stimuli were used for behavioral testing for both infants and adults, respectively. All stimuli were calibrated in dB HL. Thresholds were compared across frequency and between stimulus presentation modes, between age groups and assessment method. Normal levels for AC and BC ASSRs to AM stimuli were also calculated. The findings indicated that BC thresholds were, on average, 7 to 16 dB poorer for ASSR compared with visual reinforcement audiometry (VRA), but varied widely across infants. For infants, mean ABGs of 14 to 17 dB were found for low-frequency ASSR thresholds but mean ABGs for VRA thresholds were less than 10 dB. The preliminary normal levels for ASSR AM stimuli at 500, 1000, 2000, and 4000 Hz, respectively, were: (i) AC: 30, 30, 20, and 20 dB HL, and (ii) BC: 20, 20, 30, and 30 dB HL. There was a tendency for infant and adult ASSR thresholds to differ for BC, but not for AC. Behavioral thresholds for AC and BC were similar between infants and adults and across frequency. Infant-adult and AC-BC threshold differences are greater for ASSRs compared with behavioral measures. The results support the presence of a clinically significant maturational ABG in the low frequencies for infant ASSRs but not for VRA. The findings also show a significant offset between BC ASSR and BC VRA thresholds and large intersubject variability.