Air-conducted Stimuli Research Articles

BAER Testing in a Dog with Bilateral External Ear Canal Atresia

A 3 yr old male castrated Labrador retriever presented for evaluation and treatment of bilateral atresia of the external ear canals. The owners reported that the dog could hear only loud and high-pitched noises. Computed tomography of the head revealed intact vertical and horizontal ear canals filled with debris and a debris-filled right tympanic bulla. Air- and bone-conducted brainstem auditory evoked response (BAER) testing revealed an elevated response threshold to air-conducted stimuli and greater amplitude waveforms evoked by bone-conducted stimuli. The ear canals were surgically corrected via lateral ear canal resection. BAER testing postoperatively revealed a decrease in the air-conducted BAER threshold. This case is an example of the use of bone-conducted BAER testing to aid in the diagnosis of conductive deafness, and in determining prognosis for normal hearing after surgical treatment of external ear canal atresia.

Effects of Stimulus and Recording Parameters on the Air Conduction Ocular Vestibular Evoked Myogenic Potential

Vestibular evoked myogenic potentials (VEMPs) have been recorded from the sternocleidomastoid muscle (cervical VEMP or cVEMP) and more recently from the eye muscles (ocular VEMP or oVEMP) in response to air conduction and bone conduction stimuli. Both cVEMPs and oVEMPs are mediated by the otoliths and thereby provide diagnostic information that is complementary to videonystagmography and rotational chair tests. In contrast to the air conduction cVEMP, which originates from the saccule/inferior vestibular nerve, recent evidence suggests the possibility that the air conduction oVEMP may be mediated by the utricle/superior vestibular nerve. The oVEMP, therefore, may provide complementary diagnostic information relative to the cVEMP. There are relatively few studies, however, that have quantified the effects of stimulus and recording parameters on the air conduction oVEMP, and there is a paucity of normative data. To evaluate the effects of several stimulus and recording parameters on the air conduction oVEMP and to establish normative data for clinical use. A prospective repeated measures design was utilized. Forty-seven young adults with no history of neurologic disease, hearing loss, middle ear pathology, open or closed head injury, cervical injury, or audiovestibular disorder participated in the study. The effects of stimulus frequency, stimulus level, gaze elevation, and recording electrode location on the amplitude and latency of the oVEMP for monaural air conduction stimuli were assessed using repeated measures analyses of variance in an initial group of 17 participants. The optimal stimulus and recording parameters obtained in the initial group were used subsequently to obtain oVEMPs from 30 additional participants. The effects of stimulus frequency, stimulus level, gaze elevation, and electrode location on the response prevalence, amplitude, and latency of the oVEMP for monaural air conduction stimuli were significant. The maximum N1-P1 amplitude and response prevalence were obtained for contralateral oVEMPs using a 500 Hz tone burst presented at 125 dB peak SPL during upward gaze at an elevation of 30°. The optimal stimulus and recording parameters quantified in this study were used to establish normative data that may be useful for the clinical application of the air conduction oVEMP.

Multiple Auditory Steady State Response Thresholds to Bone Conduction Stimuli in Adults With Normal and Elevated Thresholds

Auditory steady state responses (ASSRs) to multiple air conduction (AC) stimuli modulated at ∼80 Hz have been shown to provide reasonable estimates of the behavioral audiogram. To distinguish the type of hearing loss (i.e., conductive, sensorineural, or mixed), bone conduction (BC) results are necessary. There are few BC-ASSR data, especially for individuals with hearing loss. The present studies aimed to (1) determine multiple ASSR thresholds to BC stimuli in adults with normal hearing, masker-simulated hearing loss, and sensorineural hearing loss (SNHL) and (2) determine how well BC-ASSR distinguishes normal versus elevated thresholds to BC stimuli in adults with normal hearing or SNHL. Multiple ASSR and behavioral thresholds for BC stimuli were determined in two studies. Study A assessed 16 normal-hearing adults with relatively flat threshold elevations produced by 50, 60, and 70 dB SPL AC masking noise, as well as no masking. Study B assessed 10 adults with normal hearing and 40 adults with SNHL. In both studies, the multiple (500 to 4000 Hz) ASSR stimuli were modulated between 77 and 101 Hz and varied in intensity from 0 to 50 dB HL in 10-dB steps. Stimuli were presented using a B71 bone oscillator held on the temporal bone by an elastic band while participants relaxed or slept. Study A: Correlations (r) between behavioral and ASSR thresholds for all conditions combined were 0.77, 0.87, 0.90, and 0.87 for 500, 1000, 2000, and 4000 Hz, respectively. ASSR minus behavioral threshold difference scores for all frequencies combined for the no-masker, 50, 60, and 70 dB SPL masker conditions were 14.3 ± 9.2, 12.1 ± 10.4, 12.7 ± 7.7, and 11.4 ± 8.1 dB, respectively. Study B: The difference scores for 500, 1000, 2000, and 4000 Hz were, on average, 15.7 ± 12.3, 10.3 ± 10.7, 9.7 ± 10.3, and 5.7 ± 7.9 dB, respectively, with correlations of 0.73, 0.84, 0.87, and 0.94 for the normal-hearing and SNHL groups combined. The ASSR minus behavioral difference scores were significantly larger for 500 Hz and significantly smaller for 4000 Hz compared with 1000 and 2000 Hz. Across all frequencies, the BC-ASSR correctly classified 89% of thresholds as "normal" or "elevated" (92% correct for 1000, 2000, and 4000 Hz). The threshold difference scores and correlations in individuals with SNHL are similar to those in normal listeners with simulated SNHL. These difference scores are also similar to those shown by previous studies for the AC-ASSR in individuals with SNHL, at least for 1000 to 4000 Hz. The BC-ASSR provides a reasonably good estimate of BC behavioral threshold in adults, especially between 1000 and 4000 Hz. Further research is required in infants with hearing loss.

Normal Characteristics of the Ocular Vestibular Evoked Myogenic Potential

Stimulus-evoked electromyographic changes can be recorded from the extraocular muscles. These short-latency negative-polarity evoked myogenic potentials are called ocular vestibular evoked myogenic potentials (oVEMPs). To date there has not yet been a large-scale study examining the effects of age on the amplitude, latency, threshold, and interaural differences of the oVEMP to air-conducted stimuli. Further, before the oVEMP can become a useful clinical tool, the test-retest reliability of the response must be established. The oVEMP response, once more completely understood, may provide diagnostic information that is complementary to the cervical vestibular evoked myogenic potential (cVEMP; i.e., sternocleidomastoid muscle). To describe the normal characteristics of oVEMP in a cohort of age-stratified subjects, to assess the test-retest reliability of the oVEMP, and to determine if reference contamination occurs using a common recommended infraorbital reference electrode derivation. A prospective, descriptive study design was used for an investigation with a threefold purpose in which oVEMP recordings were made from the extraocular muscles (e.g., inferior oblique muscle). Fifty otologically and neurologically normal adults and children served as subjects. Subjects ranged in age from 8 to 88 yr. In Investigation 1, oVEMPs were recorded from the ipsilateral and contralateral inferior oblique muscles for all subjects. The stimulus was a 95 dB nHL 500 Hz tone burst. Next, oVEMP thresholds were obtained. Amplitude, latency, and thresholds were tabulated, and descriptive statistics were used to calculate normative values. Age-related differences in oVEMP component latencies, amplitudes, interaural amplitude asymmetries (IAAs), and thresholds were determined using an analysis of variance. In Investigation 2, oVEMPs were recorded twice in 10 subjects, once (test) and once approximately 10 weeks later (retest). Test-retest reliability for the oVEMP peak-to-peak amplitude, n1 latency, p1 latency, n1 threshold, and IAA were assessed with intraclass correlation coefficients (ICCs) calculated using a two-way random-effects, absolute-agreement model. In Investigation 3, a four-channel oVEMP recording was conducted in 10 subjects. Both observational methods and paired-sample t-tests were used to evaluate the effect that reference electrode location had on the oVEMP. oVEMP responses were present bilaterally in 90% of our subjects. The upper limit of oVEMP amplitude asymmetry, defined as the mean plus two standard deviations, was 34% (mean = 14%, SD 10), and the mean n1 latency was 12.5 (SD 1.0) msec. The amplitude of the response significantly decreased and the threshold significantly increased with increasing age, with the greatest age effects occurring in subjects 50 yr and older. Test-retest reliability was acceptable (ICCs for the measurement variables ranged from .53 to .87). Using conventional recommended recording techniques, evidence of reference contamination occurred for all subjects, resulting in a mean amplitude reduction of 30% (range = 18%-43%). Age results in systematic changes in oVEMP measurement parameters. The test-retest reliability is acceptable, and reference contamination averaging 30% is guaranteed using a second infraorbital electrode as the inverting input (i.e., reference electrode) for bipolar recordings. The oVEMP can be used as a complementary diagnostic tool to the cVEMP in evaluating subjects with suspected peripheral vestibular disorders.

Binaural measurement of bone conduction click evoked otoacoustic emissions in adults and infants

Transient evoked otoacoustic emissions (TEOAEs) are usually evoked with air conduction (AC) stimuli. Only a few reports exist about OAEs where stimuli have been delivered using bone conduction (BC) by placing a bone conductor on the forehead or the mastoid. The aims of the present study were to improve the test performance of BC-TEOAEs by using a nonlinear stimulation protocol and to find out, whether this technique can be applied in newborn hearing screening. BC-TEOAEs were measured binaurally in ten normal hearing adults and in ten infants. For measurements in infants, miniaturized probes without loudspeakers were constructed to allow a complete insertion of the probe in the infant's ear canal. It could be shown that robust and valid BC-TEOAEs can be elicited using a nonlinear stimulation protocol. Findings in adults indicated that BC-TEOAEs can be measured with properties similar to AC-TEOAEs. However, mean BC-TEOAE levels were reduced by 0.8-3.7 dB depending on frequency. In view of test time, this is compensated by performing binaural recordings. Measurements in infants indicated that the screening performance of BC-TEOAEs and AC-TEOAEs may be comparable. Further studies have to investigate, whether BC-TEOAEs are more robust than AC-TEOAEs against small conductive hearing loss.

Vibratory Stimulation Transmission Pathways Measured by Subjective Threshold and DPOAE

To clarify the skull content contribution to vibratory bone stimuli transmission and to determine stimuli features, we compared auditory threshold and distortion product otoacoustic emission (DPOAE) using a bone vibrator placed at different head sites, including the eye. The best audiometric threshold and the highest DPOAE were with the vibrator either on the mastoid of the measured side or on the temple’s “ultrasound window”. Auditory threshold with the bone vibrator on the eye resembled those of the forehead and were about 10 dB higher than at the best sites. DPOAEs were clearly present when air-conducted stimuli were presented through an inserted earphone and with the bone vibrator on the eye, indicating that vibratory sound is transmitted through skull content to the inner ear. The intracranial vibratory stimuli transmission pathway thus plays a significant role, particularly at low frequencies, and possibly also when vibratory stimuli are applied to the skull bone.

Cervical Vestibular-Evoked Myogenic Potentials Using Vibration and Sound in Normal Subjects

Received January 10, 2011 Revised January 31, 2011 Accepted February 11, 2011 Address for correspondence Hong Ju Park, MD, PhD Department of OtorhinolaryngologyHead and Neck Surgery, Konkuk University School of Medicine, 1 Hwayang-dong, Gwangjin-gu, Seoul 143-701, Korea Tel +82-2-2030-7663 Fax +82-2-2030-5299 E-mail hpark@kuh.ac.kr Background and ObjectivesZZThe aim of this study was to investigate and compare the incidence and the characteristics of parameters of cervical vestibular-evoked myogenic potentials (cVEMPs) using air-conducted (AC) and bone-conducted (BC) stimulations in normal subjects. Subjects and MethodZZTwenty-four normal subjects (48 ears) with normal hearing and no previous history of dizziness were included. cVEMP responses were recorded by surface electrodes on sternocleidomastiod muscles in response to AC and BC stimuli sequentially. Variances of parameters, including thresholds, amplitudes and interaural amplitude difference ratios (IADR), were analyzed and compared. ResultsZZcVEMP responses were clearly observed in all 48 ears in both AC and BC cVEMP tests. There was no significant difference in latencies (p1 and n1). However, the thresholds in BC cVEMP testing were significantly lower than those in AC cVEMP testing, when compared to the maximum stimulation level. Interaural amplitude difference ratios showed no significant difference in between the two tests, although amplitudes at maximum stimulation intensity in BC cVEMP testing were significantly larger than those in AC cVEMP testing. ConclusionZZThis study shows that BC cVEMP testing shows lower thresholds compared to AC cVEMP testing in normal subjects, suggesting that the threshold value can be used as a parameter in detecting vestibular dysfunction in the clinic. Further studies in patients with vari ous vestibular disorders are needed. Korean J Otorhinolaryngol-Head Neck Surg 2011;54:192-6

The vestibular evoked-potential profile of Ménière’s disease

Objective To define the ocular and cervical vestibular evoked myogenic potential (oVEMP and cVEMP) profile in Ménière’s Disease (MD), we studied air-conducted (AC) sound and bone-conducted vibration (BCV)-evoked responses in 77 patients and 35 controls. Methods oVEMPs were recorded from unrectified infra-orbital surface electromyography (EMG) during upward gaze. cVEMPs were recorded from rectified and unrectified sternocleidomastoid EMG during head elevation against gravity. Responses to AC clicks delivered via headphones and BC forehead taps delivered with a mini-shaker (bone-conduction vibrator) and a triggered tendon-hammer were recorded. Results In clinically definite unilateral MD ( n = 60), the prevalence of unilateral VEMP abnormalities was 50.0%, 10.2% and 11.9% for click, minitap and tendon-hammer evoked oVEMPs, 40.0%, 22.8% and 10.7% for click, minitap and tendon-hammer evoked cVEMPs. The most commonly observed profile was abnormality to AC stimulation alone (33.3%), followed by abnormalities to both AC and BCV stimuli (26.7%). Isolated abnormalities to BCV stimuli were rare (5%) and limited to the minitap cVEMP. The prevalence of abnormalities for each of the AC VEMPs was significantly higher than for any one BCV VEMP. For click cVEMP, click oVEMP and minitap cVEMP, average Reflex Asymmetry Ratios (AR) were significantly higher in MD compared with controls. Test results for AC cVEMP, AC oVEMP, minitap cVEMP and caloric asymmetry were significantly correlated with hearing loss. Conclusions Predominance of abnormalities in oVEMP and cVEMP responses to AC sound is characteristic of MD and indicative of saccular involvement. Significance This pattern of VEMP abnormalities may enable separation of Ménière’s disease from other peripheral vestibulopathies.

Effect of Varying Phase Between Frequency and Amplitude Modulation on Bone Conduction Auditory Steady State Responses

Auditory steady state response (ASSR) testing provides a means to objectively estimate hearing levels in newborns and adults for whom behavioral tests prove difficult. When testing these patient groups, it is preferable that clear responses to both air and bone conduction stimuli are obtained in a short amount of time. Much of the literature addressing ASSRs, such as investigations of stimulus and recording parameters, have focused on air conduction ASSRs. The aim of this investigation was to study the amplitudes, latencies, and test times of bone conduction ASSRs elicited using amplitude- (AM), frequency- (FM), and mixed-modulated (MM) stimuli and provide suggestions for optimum recording parameters. Bone and air conduction multiple ASSRs were recorded from two groups of 20 normal-hearing adults using the Multiple Auditory Steady State Response research system. AM, FM, and MM sinusoidal tones were used (0.5-, 1-, 2-, and 4-kHz carrier frequencies), which were modulated between 78 and 92 Hz. AM depth was 100% and FM depth was 20%. ASSR amplitudes and latencies (calculated using the "preceding cycles" technique) were analyzed for MM phase settings across the cycle from 0° at 45° intervals and compared with AM responses. Optimum phase settings for bone and air conduction ASSRs were calculated using a sinusoidal model based on the amplitude data. Similar effects of stimulus type and carrier frequency were observed for bone and air conduction ASSRs. AM responses were larger in amplitude compared with FM responses. MM (at all phase settings tested) and AM response latencies increased with decreasing carrier frequency. MM phase setting had a significant (p < 0.01) sinusoidal effect on ASSR amplitudes, compared with AM responses, at 1, 2, and 4 kHz but not 0.5 kHz for air conduction and 1 and 2 kHz but not 0.5 and 4 kHz for bone conduction. Using a sinusoidal function to model this effect, MM phase settings (±95% confidence intervals) of 318° (295 to 350°) and 295° (290 to 310°) are predicted to evoke the largest responses for bone conduction ASSRs at 1 and 2 kHz, respectively. Phase settings of 293° (285 to 310°), 300° (280 to 310°), and 280° (255 to 330°) are predicted for air conduction ASSRs at 1, 2, and 4 kHz, respectively. MM phase setting had little effect on estimated latency. Test times were significantly (p < 0.01) affected by phase setting with both increases and decreases being observed. Test times for ASSRs at 1, 2, and 4 kHz could be significantly reduced if the estimated optimum phase settings are used. Different stimuli can significantly affect the amplitudes of bone conduction ASSRs. These effects are similar to those observed for air conduction ASSRs. MM stimuli with specific phase settings evoke larger bone conduction ASSRs compared with AM and FM stimuli alone, and calculations show that the time taken to obtain these responses is reduced. Implementation of the suggested optimum settings will promote efficient collection of bone conduction, and indeed air conduction, ASSR data.

Multiple-ASSR Thresholds in Infants and Young Children with Hearing Loss

The multiple auditory steady-state response (multiple ASSR) is a promising technique for determining thresholds for infants and children. However, there are few data for infants and young children with hearing loss where multiple-ASSR thresholds have been compared to frequency-specific gold standard (i.e., behavioral or tone-evoked auditory brainstem response [tone ABR]) measures. The study compared multiple-ASSR and tone-ABR thresholds and assessed how well "normal" ASSR levels differentiate normal from elevated thresholds. Multiple-ASSR and tone-ABR results (to air-conduction stimuli) were obtained in infants and young children with hearing loss or normal hearing. 98 infants with hearing loss (53 infants provided thresholds) and 34 infants with normal hearing. Multiple-ASSR and tone-ABR results were typically completed on the same day. Correlations between ASSR and ABR thresholds, linear regressions, and ASSR-minus-ABR threshold difference scores were calculated for each group (normal or hearing loss), and for both groups combined. Multiple-ASSR thresholds (dB HL) were strongly correlated (r = .97) with tone-ABR thresholds (dB nHL) for 500, 1000, 2000, and 4000 Hz. Mean (±1 SD) difference scores (ASSR-minus-ABR) were 10.7 ± 9.0, 9.5 ± 9.4, 9.2 ± 9.0, and 6.3 ± 9.5 dB for 500, 1000, 2000, and 4000 Hz, respectively. The previously published "normal" ASSR levels accurately differentiated normal from elevated thresholds. Out of 523 tests with elevated tone-ABR thresholds, the multiple ASSR was "normal" in only 22 tests. In these 13 infants, other ASSR frequencies were elevated, and thus the infants would not have "passed" the ASSR. There are few studies of infants and young children comparing ASSR thresholds to frequency-specific gold standard measures, especially using the multiple-ASSR technique. The present study, comparing multiple-ASSR to tone-ABR thresholds, nearly doubles the multiple-ASSR sample size in the literature. The results indicate that the multiple-ASSR and tone-ABR thresholds are strongly correlated, and the "normal" multiple-ASSR levels of 50, 45, 40, and 40 dB HL correctly classified children as having "normal" or "elevated" thresholds. However, due to the lack of air- and bone-conduction data in infants with different types and degrees of hearing loss, further ASSR research is needed.

A superior semicircular canal dehiscence-induced air-bone gap in chinchilla

An SCD is a pathologic hole (or dehiscence) in the bone separating the superior semicircular canal from the cranial cavity that has been associated with a conductive hearing loss in patients with SCD syndrome. The conductive loss is defined by an audiometrically determined air-bone gap that results from the combination of a decrease in sensitivity to air-conducted sound and an increase in sensitivity to bone-conducted sound. Our goal is to demonstrate, through physiological measurements in an animal model, that mechanically altering the superior semicircular canal (SC) by introducing a hole (dehiscence) is sufficient to cause such an air-bone gap. We surgically introduced holes into the SC of chinchilla ears and evaluated auditory sensitivity (cochlear potential) in response to both air- and bone-conducted stimuli. The introduction of the SC hole led to a low-frequency (<2000 Hz) decrease in sensitivity to air-conducted stimuli and a low-frequency (<1000 Hz) increase in sensitivity to bone-conducted stimuli resulting in an air-bone gap. This result was consistent and reversible. The air-bone gaps in the animal results are qualitatively consistent with findings in patients with SCD syndrome.

Vestibular-Evoked Myogenic Potentials

Cervical vestibular-evoked myogenic potentials (cVEMPs) are recorded from the sternocleidomastoid muscle using air conduction or bone conduction acoustic stimuli, skull taps, or transmastoid current. The diagnostic usefulness of the cVEMP has been examined for various peripheral and central vestibulopathies. Recent reports indicate that it is possible to record short-latency ocular vestibular-evoked myogenic potentials (oVEMPs) from surface electrodes below the eyes in response to air conduction and bone conduction stimuli. Both methods provide diagnostic information about otolith function. This article provides an overview of each method and highlights the similarities and differences. Several cases are presented to illustrate the relation between the results for cVEMPs and oVEMPs in patients with well-defined audiovestibular disorders.

Normal Multiple Auditory Steady-State Response Thresholds to Air-Conducted Stimuli in Infants

Multiple auditory steady-state responses (ASSRs) to stimuli modulated at approximately 80 Hz are a promising technique for threshold estimation in infants, but additional data are required. We obtained multiple ASSRs to air-conducted (AC) stimuli. There were 54 children in two age groups: > six months (N=32) and < or = six months (N=22). All infants had normal hearing by tone-evoked auditory brain stem response. ASSR thresholds, estimated from 50 percent using cumulative percent present distributions, were 36, 30, 24, and 15 dB HL at 500, 1000, 2000, and 4000 Hz, respectively. Most (> or =90%) of the infants showed present ASSRs at 49, 45, 36, and 32 dB HL at 500, 1000, 2000, and 4000 Hz, respectively, with no differences in the results of younger versus older infants. When responses were present for all stimuli for both ears, most infants showed all eight responses within five minutes. Compared to ipsilateral responses, ASSRs in the contralateral EEG (electroencephalogram) channel were smaller and often absent. Based upon these data and the literature, normal AC ASSR "screening" levels would be 50, 45, 40, and 40 dB HL at 500, 1000, 2000, and 4000 Hz, respectively. Using the multiple-stimulus ASSR, infants with normal hearing referred for diagnostic electrophysiological threshold assessment can now be quickly confirmed as having normal thresholds for four frequencies in both ears.

Auditory steady-state responses to bone conduction stimuli in children with hearing loss

The auditory steady-state response (ASSR) to air-conduction (AC) stimuli has been widely incorporated into audiological test-batteries for the pediatric population. The current understanding of ASSR to bone conduction (BC) stimuli, however, is more limited, especially in the case of infants and children. There are few reports on ASSR thresholds to BC stimuli in infants and young children, and none for infants or children with hearing loss. The objective of this study was to investigate BC ASSR thresholds in young children with normal hearing and various types and degrees of hearing loss. AC and BC ASSR thresholds are reported for 48 young children (mean age+/-SD=2.8+/-1.9 years; age range=0.25-11.5 years; 23 female). Hearing status was classified by assessing all children with a comprehensive test battery including tympanometry, diagnostic distortion-product otoacoustic emissions, click-evoked AC auditory brainstem response, AC and BC ASSR thresholds, and an otologic examination. The subjects were assigned to the categories normal hearing, conductive loss, and sensorineural loss (mild-to-moderate or severe-to-profound), for group analysis. AC and BC ASSR stimuli (carrier frequencies: 0.25-4 kHz; 67-95 Hz modulation rates; 100% amplitude and 10% frequency modulated) were presented using the GSI Audera system. Minimum levels at which spurious BC ASSR occur were established in the group of children with severe-to-profound sensorineural hearing loss (25, 40, 60, 60 and 60 dB for 0.25, 0.5, 1, 2, and 4 kHz, respectively). Children with normal hearing presented mean (1 SD) BC ASSR thresholds of 19 (9), 18 (7), 16 (11), 24 (7), and 26 (8) dB HL at 0.25, 0.5, 1, 2, and 4 kHz, respectively. Significantly lower thresholds (p<0.0001) were obtained for 0.25, 0.5 and 1 kHz than for 2 and 4 kHz. At 0.25 kHz, 39% of thresholds were at the minimum level of spurious response occurrence. More than half (54%) of the BC thresholds in the group with mild-to-moderate sensorineural hearing loss were recorded at or above the minimum levels at which spurious response occurred. In children with conductive hearing loss, the average BC ASSR thresholds corresponded closely to those in the normal hearing group except at 1 kHz and revealed an air-bone gap. Spurious bone conduction ASSR responses limit the intensity range for which the technique may be employed in infants and children, especially at lower frequencies. Consequently, the 0.25 kHz stimulus is not recommended for clinical use. In infants and young children, sensorineural hearing loss of a moderate or greater degree in the high frequencies (1-4 kHz), and of a mild or greater degree in the low frequencies (0.5 kHz), cannot be quantified using BC ASSR. This is due to the presence of the stimulus artifact. In cases of conductive hearing loss, BC ASSR can effectively quantify sensory hearing between 0.5 and 4 kHz, but interpretations must be made cautiously within the limitations of stimulus artifact occurrence across frequencies.

Transmission Pathways of Vibratory Stimulation as Measured by Subjective Thresholds and Distortion-Product Otoacoustic Emissions

To clarify the contribution of the skull contents to the transmission of bone vibratory stimuli, and to examine the characteristics of such stimuli, we compared auditory thresholds and distortion-product otoacoustic emission (DPOAE) levels with a bone vibrator placed on various sites of the head, including the eye. The best audiometric thresholds and the highest DPOAE levels were obtained with the vibrator placed on the mastoid of the measuring side, or on the "ultrasound-window" of the temple. The audiometric thresholds obtained with the bone vibrator on the eye were similar to those of the forehead, and about 10 dB higher than at the best sites. DPOAEs were clearly present when elicited by a combination of air-conducted stimuli presented through an insert earphone and with the bone vibrator placed on the eye. These results indicate that vibratory sounds can be transmitted through the skull contents to the inner ear. The intracranial transmission pathway of the vibratory stimuli may play a significant role, particularly at low frequencies, and possibly also when the vibratory stimuli are applied on the skull bone.

CVEMP Testing in Patients with a Third Mobile Window

Objective To determine the usefulness of cervical vestibular-evoked auditory potential (cVEMP) testing for the evaluation of patients with and without a third mobile window (superior canal dehiscence or large vestibular aqueduct). Methods A retrospective review of charts from patients who underwent cVEMP testing at a single tertiary referral center was performed. The cVEMP is a vestibular reflex generated by an air-conducted stimuli, causing an inhibitory potential in the ipsilateral sternocleidomastoid muscle measured by external electrodes. cVEMP results were correlated with demographic characteristics, hearing testing, diagnosis, and imaging. Mean cVEMP thresholds (at 500 Hz) and amplitudes (@ 95dB nHL and 500 Hz) were compared between ears and between patients with and without a third mobile window (TMW). Unequal variance t-Test was used to determine significance. Patients were excluded if they had a history of Meniere's disease, middle ear disease or otologic surgery. Results 63 patients received cVEMP testing, of which 8 had either unilateral or bilateral TMW. 114 non-TMW ears were compared to 10 ears with TMW. Ears with TMW had a lower mean threshold (68 dB nHL) vs. non-TMW (83 dB nHL) (p&lt;0.003) and a higher mean amplitude (321?V) vs. non-TMW (78?V)(p&lt;0.009). Conclusions Patients with TMW have lower thresholds and higher amplitudes on cVEMP testing. This study supports the use of cVEMPs to diagnose TMW in patients who present with an unexplained air-bone gap, autophony, aural fullness, or dizziness.

Normal Ipsilateral/Contralateral Asymmetries in Infant Multiple Auditory Steady-State Responses to Air- and Bone-Conduction Stimuli

Two-channel recordings of infants' air- and bone-conduction auditory brainstem responses to brief tones show ipsilateral and contralateral (to the stimulated ear) asymmetries which may be used to isolate which cochlea is the primary contributor to the response. The objective of this study was to determine whether similar ipsilateral/contralateral asymmetries are also present in the air- and bone-conduction "brainstem" (77 to 101 Hz) auditory steady-state responses (ASSRs) of infants. Two-channel ASSRs were recorded in infants (2 to 11 mo) and adults (18 to 40 yr) with normal hearing. Multiple stimuli (carrier frequencies: 500 to 4000 Hz; amplitude/frequency modulated) were presented using a B-71 oscillator on the temporal bone or an ER3-A insert earphone. Bone-conduction ASSR amplitudes, phase delays, and thresholds were obtained for the electroencephalographic (EEG) channels ipsilateral and contralateral to the oscillator temporal-bone placement. Bone-conduction ASSRs were also obtained to the stimulus presented to the opposite temporal bone (at 40 dB HL only). Air-conduction ASSR amplitudes and phase delays were obtained at 60 dB HL in each ear for the EEG channels ipsilateral and contralateral to the transducer. Infants showed more ipsilateral/contralateral asymmetries in both air- and bone-conduction ASSRs compared with adults. Mean bone-conduction ASSR thresholds in infants were 13 to 15 dB higher (i.e., poorer) in the contralateral EEG channel compared with the ipsilateral EEG channel for 500 to 4000 Hz. In adults, there were no large differences (i.e., within 1 dB) between ipsilateral and contralateral ASSR thresholds. Based on ipsilateral/ contralateral threshold differences in infants, interaural attenuation for bone-conducted stimuli was estimated to be at least 10 to 30 dB for most infants. In contrast, most adults showed little interaural attenuation for bone-conducted stimuli. ASSR amplitudes are larger and phase delays are shorter in the ipsilateral EEG channel. For infants, the difference in air-conduction ASSR amplitude between EEG channels was twice that observed for adults. Infants also had greater ASSR amplitude differences between EEG channels for bone-conduction stimuli compared with adults, but the difference was less than that seen for air-conduction stimuli. For air-conduction stimuli, infants had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel. Adults showed no significant differences in air-conduction ASSR phase delay between EEG channels. For bone-conduction stimuli, both infants and adults had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel; the differences in ASSR phase delays between EEG channels were much smaller in infants compared with adults and fewer adults had absent responses in the contralateral EEG channels compared with infants (12% versus 34%). When the transducers were switched to the opposite ear/mastoid, the infant and adult ipsilateral/contralateral asymmetries also switched. Ipsilateral/contralateral asymmetries in air- and bone-conduction ASSRs are clearly present more often and are larger in infants compared with adults. Our findings also suggest that most infants have at least 10 to 30 dB of interaural attenuation to bone-conducted stimuli. These asymmetries in the bone-conduction ASSR have potential as a clinical tool for isolating the cochlea that is contributing to the response in infants.

Preliminary Study on Vestibular-Evoked Myogenic Potential Induced by Bone-Conducted Stimuli

To study the relationship between vestibular-evoked myogenic potential evoked by air-conducted stimuli (A-VEMP) and those evoked by bone-conducted stimuli (B-VEMP). Prospective study. University Hospital. To determine the optimum stimulus conditions for B-VEMP, 40 ears of 20 healthy volunteers were used. To compare results of A-VEMP and B-VEMP, 60 ears of 30 healthy volunteers and 70 ears of 35 patients with unilateral vestibular disorder without conductive hearing loss were used. A-VEMP and B-VEMP were measured. Both examinations involved evaluation of the interaural ratio (IAR) of the p13-n23 peak-to-peak amplitude. To compare the relationship between A-VEMP and B-VEMP in healthy subjects and patients with unilateral vestibular disorder. The optimum stimulus for B-VEMP seemed to be a tone-burst sound with 8-ms duration at 250 Hz. In all healthy subjects, both A-VEMP and B-VEMP could be recorded. The mean IAR of B-VEMP (0.5 +/- 21.0%) was not significantly different from that of A-VEMP (0.2 +/- 19.4%). In patients with unilateral vestibular disorder, B-VEMP could not be detected in 10 ears in which A-VEMP also could not be detected. The IAR of A-VEMP was strongly correlated with that of B-VEMP (correlation coefficient, 0.98). The results of B-VEMP were almost the same as those for A-VEMP, at least, for patients without conductive hearing loss.

The effect of superior canal dehiscence on cochlear potential in response to air-conducted stimuli in chinchilla

A superior semicircular canal dehiscence (SCD) is a break or hole in the bony wall of the superior semicircular canal. Patients with SCD syndrome present with a variety of symptoms: some with vestibular symptoms, others with auditory symptoms (including low-frequency conductive hearing loss) and yet others with both. We are interested in whether or not mechanically altering the superior canal by introducing a dehiscence is sufficient to cause the low-frequency conductive hearing loss associated with SCD syndrome. We evaluated the effect of a surgically introduced dehiscence on auditory responses to air-conducted (AC) stimuli in 11 chinchilla ears. Cochlear potential (CP) was recorded at the round-window before and after a dehiscence was introduced. In each ear, a decrease in CP in response to low frequency (<2 kHz) sound stimuli was observed after the introduction of the dehiscence. The dehiscence was then patched with cyanoacrylate glue leading to a reversal of the dehiscence-induced changes in CP. The reversible decrease in auditory sensitivity observed in chinchilla is consistent with the elevated AC thresholds observed in patients with SCD. According to the ‘third-window’ hypothesis the SCD shunts sound-induced stapes velocity away from the cochlea, resulting in decreased auditory sensitivity to AC sounds. The data collected in this study are consistent with predictions of this hypothesis.

Multiple Auditory Steady-State Responses to Bone-Conduction Stimuli in Adults with Normal Hearing

ASSR thresholds to bone-conduction stimuli were determined in 10 adults with normal hearing using mastoid placement of the bone oscillator. ASSRs to 0-50 dB HL bone-conduction stimuli and to 30-60 dB HL air-conduction stimuli were compared. The effect of alternating stimulus polarity on air- and bone-conduction ASSRs was also investigated. Stimuli were bone- and air-conduction amplitude-modulated tones (500-4000 Hz carrier frequencies, modulated at 77-101 Hz). ASSRs were recorded using the Rotman MASTER research system. Mean (1SD) bone-conduction ASSR thresholds were 22(11), 26(13), 18(8), and 18(11) dB HL for 500, 1000, 2000, and 4000 Hz, respectively. Except for a steeper slope at 500 Hz, ASSR intensity-amplitude functions for binaural bone- and air-conduction stimuli showed the same slopes; intensity-phase-delay functions were steeper at 1000 Hz for ASSRs to bone-conduction stimuli. ASSR amplitudes and phases did not differ for single- versus alternated-stimulus polarities for both bone- and air-conduction stimuli. The steeper amplitude slope for ASSRs to 500 Hz stimuli may reflect a nonauditory contribution to the ASSR.