Gender differences in bone conduction auditory signal processing: Communication equipment design implications

Although human air conduction (AC) and bone conduction (BC) hearing are well investigated, there is a lack of information about BC hearing in most other species, the normal BC hearing thresholds have not been established. And animal model is vital for understanding the physiology of bone conduction hearing. Hence, in our study, the hearing thresholds in the guinea pigs were estimated by a regression of the amplitude of the compound action potential (CAP) with stimulation level and was found robust and gave a high resolution of the threshold level in the frequency range between 2 kHz and 20 kHz. The reference for the BC thresholds was the cochlear promontory bone velocity. This reference enables comparison of BC hearing in animals, both intra and inter species, which is independent on the vibrator and stimulation position. According to our comparable BC threshold, we can do some further research. The vibration was measured in three orthogonal directions where the dominating vibration directions was in line with the stimulation direction, here the ventral direction. The BC thresholds lay between -10 and 3 dB re 1 μm/s. The slopes of CAP growth function were similar for AC and BC at low and high frequencies, but slightly lower for BC than AC at frequencies between 8 and 16 kHz. This was attributed to differences in the stimulus levels used for the slope estimation and not a real difference in CAP slopes between the stimulation modalities. At the same time, the effect of a middle ear lesion, here modelled by severing the ossicles (ossicular discontinuity) and gluing the ossicles to the bone (otosclerosis), is investigated for both AC and BC. Two kinds of middle ear lesions, ossicular discontinuity and stapes glued to the surrounding bone, gave threshold shifts of between 23 and 53 dB for AC while it was below 16 dB when the stimulation was by BC. Statistically different threshold shifts between the two types of lesions were found where the AC threshold shifts for a glued stapes at 2 and 4 kHz were 9 to 18 dB greater than for a severed ossicular chain, and the BC threshold shifts for a glued stapes at 4 and 12 kHz were 8 to 9 dB greater than for a severed ossicular chain. Moreover, the direction of the vibration influences BC hearing also is investigated in our study. This direction sensitivity was investigated guinea pigs by providing BC stimulation in five different directions at the vertex of the guinea pig skull. The hearing thresholds for BC stimulation was obtained in the frequency range of 2 to 20 kHz by measurements of the guinea pigs’ compound action potential. During the stimulation by BC, the vibration of the cochlear promontory was measured with a three-dimensional laser Doppler vibrometer resulting in a set of unique three-dimensional vibration combinations for each threshold estimation. The sets of three-dimensional vibration at threshold were used to investigate six different predictors of BC hearing based on cochlear promontory vibration, three single direction (x, y and z directions in isolation), one linear combination of the three-dimension vibrations, one square-rooted sum of the squared vibration magnitudes, and one sum of the weighted three-dimensional vibrations based on a restricted minimum mean square error (MMSE) estimation. The MMSE gave the best predictions of the hearing threshold based on the cochlear promontory vibration while using only a single direction gave the worst predictions of the hearing thresholds overall. According to the MMSE estimation, at frequencies up to 8 kHz the vibration direction between the right and left side gave the greatest contribution to BC hearing in the guinea pig while at the highest frequencies measured, 16 and 20 kHz, the anteroposterior direction of the guinea pig head gave the greatest contribution. We do the further research to compare the vibrational patterns of human and guinea pig cochleae accurately, we developed and validated a novel finite element model of the guinea pig, leveraging it to analyze vibrational patterns in the cochlea. This approach is mirrored in our examination of the human cochlear model, providing granular insights into the nuances of human bone conduction hearing. The comparative analysis reveals that the guinea pig cochlea mirrors human cochlear vibrational patterns, thus serving as an efficient proxy for exploring human cochlear function. The convenient and comparable sites for bone conduction stimulation are identified as the human mastoid and the upper region of the guinea pig's skull. The cochlear vibration pattern encompasses a mix of rigid, rotational, and compressive motion.

Background: Two different pathways of sound transmission to the inner ear are differentiated; air conduction (AC) and bone conduction (BC). The transmission pathway of AC, which is physiological for human hearing, implies the transmission of sound to the cochlea via the ear canal, eardrum, and middle-ear ossicles, while BC bypasses the Pinna, the external auditory canal and the middle ear. The transmission pathway by BC has not been fully understood and many aspects still remain questionable. The aim of this study is to characterize two ways of direct transmission of vibrations to the inner ear by measuring hearing thresholds and vibrations of the skull. The bone-vibrator, which is usually used to measure the BC hearing thresholds in contact with the mastoid, can also be used to simulate other contents of skull, such as the eye. Methods: Ten adults (age range of 25-40) with normal hearing and five patients (age range of 21-31) with single sided profound deafness (SSD) were included in this study. The AC audiometry by pure tones was measured using insert earphones and the BC audiometry was measured by stimulating four different locations of the skull; the forehead, the temporal region, the mastoid, and the ipsilateral eyeball with two different contact pressure magnitudes of 2N and of 5N. The vibrations of the skull bones induced by air and bone conduction stimuli were measured by an accelerometer positioned between an upper and lower front incisor tooth. Results: The BC hearing thresholds by stimulating the temporal region and the mastoid were the lowest in both of normal hearing and SSD subjects and the values by both stimulations were similar. Thresholds were significantly higher for stimulations on the forehead and the eye (p<0.05). The difference between the thresholds by stimulation at the mastoid or temporal region and at the eye was more pronounced in SSD subjects (p<0.01). The averaged BC thresholds of normal subjects by stimulation on the contralateral temporal region were significantly lower than the averaged BC thresholds of SSD subjects only at the frequency of 0.25 kHz (p<0.01). The BC thresholds by stimulation on the contralateral mastoid of the normal hearing subjects were significantly lower in 5 N headband than in 2 N headband at the whole frequency range (p<0.05). The BC thresholds by stimulation on the ipsilateral mastoid of the normal hearing subjects showed significant differences between the contact pressure forces of 5 N and 2 N at the frequencies of 1, 2, and 3 kHz (p<0.5). The stimulation on the contralateral mastoid with the 5 N headband resulted in a significantly lower BC threshold than the stimulation with 5 the 2 N headband at the entire frequency range (p<0.05). In SSD subjects, the stimulation on the ipsilateral mastoid side with the 5 N headband had a significantly lower BC thresholds than stimulation with the 2 N headband at all frequencies except for 0.5 and 4 kHz (p<0.05). The BC thresholds in normal hearing subjects were significantly lower with the ipsilateral temporal stimulation than with a corresponding contralateral stimulation for the all frequencies except for 0.5 and 1 kHz (p<0.01). For the SSD subjects, the BC thresholds with the ipsilateral temporal stimulation were significantly lower at 2, 3 and 4 kHz than those with the corresponding contralateral stimulation. Skull vibrations in the normal hearing subjects showed similar behaviors at low frequencies up to 2 kHz for all stimulations except for stimulation on the eye, where vibrations were smaller. In contrast, skull vibrations measured from stimulation at the eye were increasing with higher frequencies. Under 2 kHz skull vibrations at eye were significantly smaller than those from stimulation of the mastoid, but above 2 kHz, they were significantly bigger (p<0.05). Skull vibrations between stimulation at the ipsilateral mastoid and forehead were significantly different at 0.25, 3 and 4 kHz (p<0.05). The subjects with SSD showed similar patterns. Conclusion: The patterns of BC hearing thresholds were similar in normal subjects and subjects with SSD. Hearing thresholds in all subjects were significantly better for mastoid and temple stimulation compared to eye stimulation. One reason for that may be the different pressures applied. Skull vibrations as measured at teeth did not match the same pattern as the hearing thresholds. Eye stimulation induced low vibrations below 2 kHz, but high vibrations above 2 kHz. This finding demonstrates special acoustic properties of the living organism, the distance from stimulation might also contribute. Skull-bone vibrations decreased with increasing frequency for mastoid and temple stimulation. Stimulation of soft tissue, presumably including skull contents, seems to induce high frequency skull vibrations. That might be involved with the distance form the front teeth. The transcranial attenuation of vibration should be considered especially in high frequencies.

Bone conduction hearing in the Guinea pig and the effect of artificially induced middle ear lesions

The aim of this study is to investigate how a mastoidectomy surgery affects bone conduction (BC) sound transmission using a whole head finite element model. Air conduction (AC) and BC hearing thresholds are normally used to evaluate the effect of an ear surgery. It is then assumed that the BC hearing thresholds are unaffected by the surgery. Moreover, BC hearing aids are used in cases of unilateral or conductive hearing loss in heads that have undergone a mastoidectomy surgery. Given the invasiveness of the surgery, the BC hearing sensitivity may be altered by the surgery itself. Two types of mastoid surgery, canal wall up and canal wall down, with and without obliteration, were simulated in a whole head finite element model for BC stimulation, the LiUHead. The evaluations were conducted for two different methods of applying the BC sound, at the skin surface (B71 transducer) and directly at the bone (BC hearing aid). The results showed that a mastoidectomy surgery increased the cochlear vibration responses with BC stimulation. The increase was less than 5 dB, except for a canal wall down surgery which gave an increase of up to 8 dB at frequencies close to 10 kHz. The increase was greater at the ipsilateral cochlea compared with the contralateral cochlea. A mastoidectomy surgery increases the vibration at both cochleae for BC stimulation and the increase generally improved with frequency. Obliteration of the surgical cavity does not influence BC sound transmission.

Background: Simple or non-syndromic types of oval window (OW) or round window (RW) atresia are relatively rare in clinical. Few studies have assessed bone conduction (BC) hearing in OW or RW atresia patients, with some reporting that BC hearing lies within the normal range, whereas others observing impaired BC hearing.Aims/Objectives: This study explored the effect of blocking the OW and RW during BC in cat models.Material and Methods: Twenty-four cats were randomly divided into three immobilization groups (OW blockage, RW blockage, and OW + RW blockage) and control group. Each immobilization group also had the initial control state before blockage. Medical adhesive and ear mould glue were used to immobilise the stapes footplate and RW, respectively. Comparisons were made of the auditory brainstem response (ABR) thresholds before and after immobilization for the three immobilization groups during three different stimuli [air conduction (AC) click, BC click, and BC pure tones].Results: The AC click thresholds increased after immobilisation in three experimental groups compared to the control group (p < .05). The AC click thresholds increased compared to their initial control state after all three immobilization groups (p < .05). With an increase in frequency from 2 to 8 kHz, there was a general decrease in the difference between pre- and post-immobilization BC hearing thresholds in all three immobilization groups. The BC click threshold and BC tone thresholds at 2–4 kHz in both OW blockage and OW + RW blockage groups exceeded those in RW blockage group (p < .05).Conclusions and Significance: The use of medical adhesive and ear mould glue for the blockages of OW and RW, respectively in cats was feasible. The effect of blocking the OW and RW in BC hearing was larger at low frequencies than high frequencies between 2 and 8 kHz. OW blockage had a greater effect than RW blockage on BC hearing at 2–4 kHz range.

The purpose of this study was to measure air-conduction (AC) and bone-conduction (BC) hearing thresholds with pure-tone and filtered sound effect stimuli using standard audiometric equipment. A group of 20 young, normal-hearing listeners participated in the study. Pure-tone stimuli were 250, 500, 1000, 2000, and 4000 Hz. Sound effect stimuli were 12 natural sounds that were spectrally limited to an octave bandwidth centered at either 250, 500, 1000, 2000, or 4000 Hz. The AC and BC detection thresholds were measured using a clinical audiometer (Madsen Orbiter 922) with a B-71 bone oscillator and TDH-50 earphones. Results indicated that detection thresholds for the pure-tone and corresponding octave-band sound effect stimuli were within 3 to 4 dB of each other for both AC and BC testing. The findings support the notion that octave-filtered sound effects are a viable alternative to pure-tone stimuli for use in audiology clinics.

Air conduction (AC), bone conduction (BC), and underwater-hearing thresholds were obtained on three samples of underwater swimmers. In Sample I, AC and BC hearing levels varied over a considerable range at the higher frequencies. Underwater hearing thresholds were positively correlated with BC thresholds. The loss of sensitivity upon immersion was negatively correlated with AC hearing levels. In Sample 2, underwater hearing thresholds of three divers having depressed AC hearing levels at 6 kHz and two divers having depressed AC and BC hearing levels were compared with underwater hearing levels of eight normal-hearing divers. Depressed underwater hearing levels occurred for the divers having combined AC and BC losses. Divers exhibiting only AC losses heard as well underwater as normal hearing divers. Maximum sensitivity for the normal hearing divers over the frequency range 1–8 kHz was −20 dB/μbar at 1 kHz. In a third sample, data were obtained on threshold sensitivity over the 125-Hz to 8-kHz frequency range. Maximum sensitivity of −23 dB/μbar was observed at 1 kHz.

ObjectiveTo evaluate the clinical efficacy and safety of hydrogen inhalation in improving hearing loss in patients with long-term survival of nasopharyngeal carcinoma after radiotherapy.MethodsThe eustachian tube dysfunction score, pure tone air conduction threshold, bone conduction threshold, the score of tympanogram and otoscope were prospectively observed in patients with deafness after radiotherapy only or combined radiotherapy and chemotherapy for nasopharyngeal carcinoma. Paired t test and one-way analysis of variance were used to analyze the data before and after treatment.ResultsA total of 17 patients were observed. The median time from radiotherapy to now was 228 months, and the median time from the diagnose of deafness to now was 92 months. After 4 weeks of hydrogen inhalation, the score of eustachian tube dysfunction, air conduction and bone conduction hearing thresholds were significantly reduced, P values were 0.0293, 0.0027, 0.0404, respectively. The mean air-bone gap, the score of otoendoscopy and tympanogram were also decreased, but the differences were not significant (P = 0.2079, P = 0.0536, P = 0.1056). Patients with radiotherapy alone and concurrent chemo-radiotherapy had significantly lower air conduction hearing threshold after hydrogen absorption (P = 0.0142, P = 0.0495). The results of air and bone hearing thresholds before, 4 and 12 weeks after hydrogen inhalation showed a descending trend. The air and bone hearing thresholds before hydrogen inhalation were 74.69 ± 27.03 dB and 45.70 ± 21.58 dB, respectively. At the 12th week, the mean values of air and bone hearing thresholds were the lowest, which were 66.88 ± 20.88 dB and 40.94 ± 18.93 dB, respectively, but there was no significant difference in air and bone hearing thresholds among all groups (P = 0.6755, P = 0.7712). After hydrogen inhalation treatment, no adverse reactions such as nosebleed, chest pain, dyspnea, nausea, vomiting, dizziness, earache and allergic reaction were observed.ConclusionThis is the first prospective study on the effect of hydrogen inhalation on hearing improvement in patients with deafness after radiotherapy/chemotherapy for nasopharyngeal carcinoma, suggesting that continuous hydrogen inhalation may be an alternative rehabilitation therapy for these patients.

In order to differentiate between a conductive hearing loss (CHL) and a sensorineural hearing loss (SNHL) in the hearing-impaired individual, we compared thresholds to air conduction (AC) and bone conduction (BC) auditory stimulation. The presence of a gap between these thresholds (an air-bone gap) is taken as a sign of a CHL, whereas similar threshold elevations reflect an SNHL. This is based on the assumption that BC stimulation directly excites the inner ear, bypassing the middle ear. However, several of the classic mechanisms of BC stimulation such as ossicular chain inertia and the occlusion effect involve middle ear structures. An additional mode of auditory stimulation, called soft tissue conduction (STC; also called nonosseous BC) has been demonstrated, in which the clinical bone vibrator elicits hearing when it is applied to soft tissue sites on the head, neck, and thorax. The purpose of this study was to assess the relative contributions of threshold determinations to stimulation by STC, in addition to AC and osseous BC, to the differential diagnosis between a CHL and an SNHL. Baseline auditory thresholds were determined in normal participants to AC (supra-aural earphones), BC (B71 bone vibrator at the mastoid, with 5 N application force), and STC (B71 bone vibrator) to the submental area and to the submandibular triangle with 5 N application force) stimulation in response to 0.5, 1.0, 2.0, and 4.0 kHz tones. A CHL was then simulated in the participants by means of an ear plug. Separately, an SNHL was simulated in these participants with 30 dB effective masking. STUDY SAMPLE consisted of 10 normal-hearing participants (4 males; 6 females, aged 20-30 yr). AC, BC, and STC thresholds were determined in the initial normal state and in the presence of each of the simulations. The earplug-induced CHL simulation led to a mean AC threshold elevation of 21-37 dB (depending on frequency), but not of BC and STC thresholds. The masking-induced SNHL led to a mean elevation of AC, BC, and STC thresholds (23-36 dB, depending on frequency). In each type of simulation, the BC threshold shift was similar to that of the STC threshold shift. These results, which show a similar threshold shift for STC and for BC as a result of these simulations, together with additional clinical and laboratory findings, provide evidence that BC thresholds likely represent the threshold of the nonosseous BC (STC) component of multicomponent BC at the BC stimulation site, and thereby succeed in clinical practice to contribute to the differential diagnosis. This also provides evidence that STC (nonosseous BC) stimulation at low intensities probably does not involve components of the middle ear, represents true cochlear function, and therefore can also contribute to a differential diagnosis (e.g., in situations where the clinical bone vibrator cannot be applied to the mastoid or forehead with a 5 N force, such as in severe skull fracture).

Objective The false sensorineural loss caused by otosclerosis due to stapes fixation is known as the Carhart notch. To examine the changes in air-bone gap (ABG) and bone-conduction (BC) hearing thresholds by comparing the preoperative and postoperative audiometry results in patients with chronic otitis media (COM), to investigate the effects of air conduction (AC) on BC, to determine the effects of postoperative improvement in AC on BC, to detect the presence of the Carhart notch in COM, and to determine the effects of surgery on the Carhart notch. Material and Methods A total of 104 patients who underwent type 1 tympnoplasty between January 2012 - March 2017 in our clinic were included in this retrospective study. Parameters measured during the preoperative and postoperative sixth month audiometric evaluation comprised AC hearing thresholds at the frequencies of 250-8,000 Hz, BC hearing thresholds at 500-4,000 Hz, and ABG values at 500-4,000 Hz intervals. Results Before surgery, the Carhart notch was present in 46 (44.2%) of the 104 patients. Postoperatively, the Carhart notch was observed to have been corrected in 25 (54.3%) of these patients (p=0.029). Conclusion After tympanoplasty, significant improvement in ABG may lead to improvement in BC at 2,000 Hz in COM cases with an intact and mobile ossicular chain. The Carhart notch may also be present in COM.

This study aimed to analyze the predictability of temporal bone (TB) fracture-associated hearing loss by applying a detailed classification separating individual injury of the cochlea, vestibule, and semicircular canals (SCC). In this retrospective study, patients with otic capsule-violating (OCV) fractures were further classified as OCV-C(VS) when the cochlea was involved regardless of vestibule or SCC involvement, OCV-V(S) when the vestibule was involved regardless of SCC involvement, and OCV-S when the fracture only involved SCC. Hearing changes were compared by applying the above-mentioned classification, and TB fracture-induced facial palsy was also analyzed. A total of 119 patients were included. Patients with OCV fractures had significantly worse bone conduction (BC) and air conduction (AC) thresholds (59.1 ± 25.3 and 87.0 ± 29.5 dB) than those with otic capsule-sparing (OCS) fractures (20.1 ± 17.9 and 36.5 ± 21.9 dB; p < 0.001 for each comparison). The BC and the AC thresholds of OCV-C(VS) (77.5 ± 11.0 and 114.2 ± 14.3 dB) and OCV-V(S) (69.3 ± 27.7 and 98.0 ± 22.2 dB) were significantly higher than OCV-S (40.1 ± 22.9 and 62.1 ± 25.6 dB; p < 0.001 for each comparison). The BC hearing thresholds were not significantly improved in the last pure tone audiometry when compared for total, OCV, or OCS cases. The AC threshold significantly improved in OCS cases. In a considerable number of cases with facial palsy, causative fracture lines involved the geniculate ganglion or tympanic segment without the involvement of the otic capsule. Most cases showed significant improvement; however, recovery was limited in cases with obvious fallopian canal disruption. The cases with sole involvement of SCC had significantly better hearing thresholds than those with cochlear or vestibule involvement, even in OCV fracture cases.

Besides the normal hearing pathway known as air conduction (AC), sound can also transmit to the cochlea through the skull, known as bone conduction (BC). During BC stimulation, the cochlear walls demonstrate rigid body motion (RBM) and compressional motion (CPM), both inducing the basilar membrane traveling wave (TW). Despite numerous measuring and modeling efforts for the TW phenomenon, the mechanism remains unclear, especially in the case of BC. This paper proposes a 3D finite element cochlea model mimicking the TW under BC. The model uses a traditional "box model" form, but in a spiral shape, with two fluid chambers separated by the long and flexible BM. The cochlear fluid was enclosed by bony walls, the oval and round window membranes. Contingent boundary conditions and stimulations are introduced according to the physical basis of AC and BC. Particularly for BC, both RBM and CPM of the cochlea walls are simulated. Harmonic numerical solutions are obtained at multiple frequencies among the hearing range. The BM vibration amplitude ([Formula: see text]) and its relation with volume displacement difference between the oval and round windows [Formula: see text], as well as the pressure difference at the base of the cochlea ([Formula: see text]), are analyzed. The simulated BM response at 12mm from the base is peaked at about 3kHz, which is consistent with published experimental data. The TW properties under AC and BC are the same and have a common mechanism. (1) [Formula: see text] is proportional to [Formula: see text] at low frequencies. (2) [Formula: see text] is also proportional to [Formula: see text], within 5dB error at high frequencies such as 16kHz. This study partly reveals the common quantitative relations between the TW and related factors under AC and BC hearing.

e18069 Background: Lateral temporal bone resection (LTBR) is used to treat malignancies originating from the auricle, periauricular skin, external auditory canal, parotid gland, or temporal bone. LTBR is the workhorse of otologic cancer surgery; however, few studies have described audiologic outcomes in a large sample of patients. The current literature focuses on overall survival rates post-surgery; however, hearing loss-related outcomes after surgery and adjuvant therapy are lacking in the literature. Following surgery, patients are expected to have maximal conductive hearing loss in the affected ear which can be augmented by ototoxic effects of adjuvant treatment such as radiation and systemic therapy. This type of hearing loss significantly impacts quality of life, making it difficult to understand speech directed to the surgically closed ear, localize sounds, and understand conversational speech in noisy environments. Less is known about the rate and severity of sensorineural hearing loss (SNHL) following LTBR. Methods: A retrospective chart review was conducted among 252 patients who underwent LTBR at single tertiary care center from 2010 to 2020. We evaluated changes in ipsilateral bone conduction (BC) hearing thresholds after LTBR ± adjuvant therapy, including head and neck radiation, chemotherapy, and immunotherapy. Patients who completed at least 1 preoperative and 1 postoperative audiogram within 2 years of surgery were included. Patients who had preoperative chemotherapy, immunotherapy, or temporal bone radiation were excluded. Of 252 patients reviewed, 94 met the eligibility criteria. Audiometric data included pure tone average (PTA) for BC thresholds. A significant decline in hearing was defined as an increase in PTA ≥ 10 decibels (American Academy of Otolaryngology-Head and Neck Surgery). Three treatment subgroups were analyzed, including LTBR only, LTBR and radiation therapy, and LTBR with radiation and systemic therapy. Results: Among all patients, BC PTA increased on average by 7dB after treatment (p&lt;0.001); 30% of patients had ≥ 10dB shift. Patients undergoing LTBR with adjuvant therapy had a higher rate of hearing loss compared to patients undergoing LTBR alone (22/69, 32% vs. 5/25, 20%, respectively). Conclusions: LTBR can cause significant long-term decline in BC hearing that is worsened with the addition of adjuvant therapy. Therefore, it is critical to systematically obtain preoperative and post-treatment audiologic testing to monitor and rehabilitate hearing loss over time. The findings of this study may help patients understand realistic expectations of long-term treatment outcomes related to hearing loss, as an initial step to help improve quality of life with hearing rehabilitation such as osseointegrated bone conduction devices.

We sought to compare the long-term functional results of tympanic membrane reconstruction with temporalis fascia and cartilage shield grafting. This study includes 113 patients who had tympanoplasty type I tympanic membrane reconstruction between 1997 and 2007, 47 with tragal cartilage and 66 with temporalis fascia. Fourteen patients in the cartilage group and 9 patients in the temporalis fascia group also had mastoidectomy. The average follow-up was 3.2 years. The hearing threshold was calculated as the mean value of the thresholds for 500, 1,000, 2,000, and 3,000 Hz. A paired-samples t-test was used for comparison of the preoperative and postoperative air and bone conduction hearing thresholds and air-bone gaps. Significant recovery was found in the postoperative air conduction threshold and air-bone gap in both the temporalis fascia and cartilage groups as compared to those before surgery (p < 0.001). However, the average air and bone conduction thresholds and air-bone gap were found to be statistically different after surgery in the cartilage group as compared to those in the temporalis fascia group. There was no significant difference in hearing parameters before and after surgery in patients with or without mastoidectomy in either the cartilage group or the temporalis fascia group. The hearing gain in patients with cartilage shield grafting was better than that in those who had temporalis fascia tympanoplasty, although experimental analysis shows loss of acoustic energy for thick and large shield cartilage grafts.

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.