Test Ear Research Articles

The vestibular evoked myogenic potential: A test–retest reliability study

The purpose of this study was to evaluate the reliability of the vestibular evoked myogenic potential (VEMP) response in a clinical setting when only a feedback mechanism is available for monitoring background EMG. Sixty-one healthy subjects participated in the investigation of the within-session reliability, whereas fourteen of them were retested after one week for examination of the between-session reliability. VEMPs were recorded using 500 Hz tone bursts with the subjects in a sitting position and their heads turned away from the test ear to the contralateral shoulder, thereby pushing their chin against the inflatable cuff of a blood pressure manometer, serving as feedback method. The feedback method revealed latency and amplitude values comparable to other data in the literature where different test conditions were applied. Excellent reliability with ICC values ranging from 0.78 to 0.96 and CV(ME) values ranging from 4% to 36%, was achieved for P1 and N1 latency, threshold and interpeak amplitude. Good reliability with ICC values of 0.65 and 0.68 and CV(ME) values of 170% and 189%, was obtained for the asymmetry ratio. A unilateral muscle contraction controlled by a feedback mechanism resulted in reliable response parameters, comparable right to left and corresponding to literature data obtained in different test conditions. The use of a blood pressure manometer as feedback mechanism combined with a meticulously controlled positioning of the head and contraction of the SCM muscle provides a reliable alternative in clinical settings, when the background muscle contraction cannot be measured or software related correction algorithms are not accessible.

Automatic segmentation of the facial nerve and chorda tympani in CT images using spatially dependent feature values

In cochlear implant surgery, an electrode array is permanently implanted in the cochlea to stimulate the auditory nerve and allow deaf people to hear. A minimally invasive surgical technique has recently been proposed-percutaneous cochlear access-in which a single hole is drilled from the skull surface to the cochlea. For the method to be feasible, a safe and effective drilling trajectory must be determined using a preoperative CT. Segmentation of the structures of the ear would improve trajectory planning safety and efficiency and enable the possibility of automated planning. Two important structures of the ear, the facial nerve and the chorda tympani, are difficult to segment with traditional methods because of their size (diameters as small as 1.0 and 0.3 mm, respectively), the lack of contrast with adjacent structures, and large interpatient variations. A multipart, model-based segmentation algorithm is presented in this article that accomplishes automatic segmentation of the facial nerve and chorda tympani. Segmentation results are presented for ten test ears and are compared to manually segmented surfaces. The results show that the maximum error in structure wall localization is approximately 2 voxels for the facial nerve and the chorda, demonstrating that the method the authors propose is robust and accurate.

Air-Conduction Auditory Steady-State Response: Comparison of Interchannel Recording Using Two Modulation Frequencies

Two-channel auditory steady-state response (ASSR) recording at high and low MF (modulation frequency) most likely provides an insight about the response amplitude and latency from different directions at the brainstem level and at the thalamus or cortical level. Little is known about the combined relationship between MF (39 and 79 Hz) and electrode montages (ipsilateral and contralateral) to single AM (amplitude modulation) tones on the ASSR amplitude and latency. To determine if ipsilateral versus contralateral response asymmetries are present at the brainstem level (79 Hz ASSR) and at the thalamus or cortical levels (39 Hz ASSR). Descriptive and inferential statistics for interchannel ipsilateral and contralateral ASSR amplitude and latency to 79 and 39 Hz. Twenty-five normal-hearing, right-handed young female adults participated in the study. All participants were right-handed, and their age ranged between 18 to 28 years (mean 24.5 +/- 1.6 years). Ipsilateral and contralateral ASSR to 39 and 79 Hz MF and 100% AM stimuli were recorded at 500, 2000, and 4000 Hz carrier frequencies at 65 dB SPL. The ASSR amplitudes and phases were determined for each MF across Fc (carrier frequency) for the two channels to the test (right) ear. ASSR amplitude and latency between recording montages for each MF and across carrier frequency were compared by computing two-way repeated measures ANOVA. The mean ipsilateral ASSR amplitudes to 39 Hz across frequency were slightly larger (228.6 +/- 61.6 microV) than the contralateral response amplitude (223.2 +/- 78 microV) while the mean ipsilateral 79 Hz amplitudes were smaller (127.3 +/- 114.8) compared to contralateral 79 Hz amplitude (154.6 +/- 112.7 microV). For latency response, the mean ipsilateral/contralateral latency difference, on average, was 1 msec or less for both MFs. Results, in normal female adults, indicated no significant interchannel ASSR asymmetries for amplitude and latency (p > 0.05) at the brainstem (79 Hz ASSR) and at the thalamus or cortical levels (39 Hz ASSR). Interchannel ipsilateral and contralateral ASSR amplitude and latency to 79 and 39 Hz are not significantly different in normal, young female adults. Two-channel recording of ASSR to different MFs may be of clinical value in otoneurologic assessment.

The Effects of “Central Masking” on Test Ear Latencies in Auditory Brainstem Responses: Preliminary Results

AbstractIn a 1996 study, we encountered an important question: “Can a masker noise affect the test ear during the masking process in ABR testing? And “What is the route of this effect? During that study, we found that the masker noise affected the nontest ear, even with low intensities of noise. These effects seemed to be related to “central masking.” In 2006, we performed a study on 9 males using a new method. White noise was delivered to the nontest ear at five levels (0, 10, 20, 30, and 40 dB SPL), while the click of 125-μsec duration was constantly kept at 120 dB SPL in all stages and delivered to the test ear. The absolute latencies of I, III, and V waves and also interpeak latencies (IPLs) of I–V, I–III, and III–V were then measured and recorded. The results showed that in the right ear the absolute latencies of I, III, and V waves decreased, up to 20 dB SPL of noise, and after 30 dB SPL, absolute latency inlatcreased. However, this effect was not seen in the left ear. A survey of IPLs in both ears ...

Noise levels during aerobics and the potential effects on distortion product otoacoustic emissions

The purpose of this study was to measure noise levels during aerobics classes and to examine how outer hair cell (OHC) function, using distortion product otoacoustic emissions (DPOAEs), may be affected by this exposure. Fifty individuals (48 women and 2 men, ages 19–41 years) participated in 50-min aerobics classes. Noise levels were measured using noise dosimeters placed on the collar near the test ear. The audiometric protocol consisted of a questionnaire, otoscopy, screening tympanometry, and pre- and post-aerobics DPOAEs. The minute-by-minute peak noise levels varied between 90.5 and 99.7dBA. The overall mean noise level for the aerobics classes was 87.1dBA (range=83.4–90.7dBA). Mean post-aerobic DPOAE levels were lower at most frequencies with a statistically significant 1.4dB decrease at 6000Hz. Results of this project, even with limited statistical significance, should be viewed cautiously.Learning outcomes: The reader will be able to (1) identify the approximate dB SPL measured during aerobics classes, (2) describe what effects, if any, these levels had on DPOAEs, and (3) discuss what specific frequency had a significant decrease in DPOAE level after an aerobics class.

Formulation and evaluation of less-painful clarithromycin lipid microspheres

Lipid microspheres (LMs) have recently been use as drug carriers for intravenous use due to its low toxicity, good physiological tolerance and the reduction of the drug related side-effect. In this study, clarithromycin was incorporated in LMs, in an attempt to reduce the pain caused by intravenous use. The composition of the drug loaded LMs was clarithromycin 0.5%, oil phase 10%, soybean phospholipid 2%, egg lecithin 0.5%, Sodium oleate 0.1%. Clarithromycin LMs was prepared by high pressure homogenization method at 80 MPa for 8-10 cycles. The mean particle size and surface charge of LMs were 208.7+/-7.8 nm and -23.6+/-2.3 mv respectively. Clarithromycin entrapment efficiency in LMs was 66.4%. Drug loaded LMs was stable during the storage time at 6+/-2 degrees C for 9 month, and the particle size and zeta-potential did not change significantly. Drug concentration in LMs was 5 mg/mL, and there was no drug degradation during long term storage. Animal tests (rat paw lick test and rabbit ear vein irritation test) were used to evaluate the pain reduction of clarithromycin LMs compared with that of clarithromycin aqueous solution. These results suggest that the LM system is a promising option to replace clarithromycin aqueous solutions as an intravenous treatment.

Effects of Cueing in Auditory Temporal Masking

In a landmark study, B. A. Wright et al. (1997) reported an apparent backward-masking deficit in language-learning-impaired children. Subsequently, the controversial interpretation of those results has been influential in guiding treatments for childhood language problems. This study revisited the temporal-masking paradigm reported by B. A. Wright et al. to evaluate adult listener signal/masker uncertainty effects for some of their key stimulus conditions. New signal conditions presented off frequency from the masker also were evaluated to assess conditions of reduced signal/masker confusion. Masked detection was measured for 20-ms sinusoids (480, 1000, or 1680 Hz) presented at temporal positions before, during, or after a gated narrowband (bandwidth = 600-1400 Hz) masker. Listener uncertainty was investigated by cueing various stimulus temporal properties with a 6000-Hz sinusoid presented contralateral to the test ear. The primary cueing effect was measured in the backward-masking condition for the cue gated simultaneously with the on-frequency 1000-Hz signal. The resulting cued masked-detection threshold was reduced to quiet threshold. No significant cueing effects were obtained for other signal temporal positions in the masker or for any off-frequency signal conditions. These results for normal adult listeners indicate that on-frequency backward masking can be eliminated by cueing the signal, and thus, these findings raise the possibility that the deficit reported by B. A. Wright et al. for language-learning-impaired children may reflect inordinate signal/masker confusion, rather than a temporal-processing deficit per se.

Does the method of sternocleidomastoid muscle activation affect the vestibular evoked myogenic potential response?

The objective of this study was to assess the effects of different methods of sternocleidomastoid muscle (SCM) activation on vestibular evoked myogenic potentials (VEMP). Forty normal volunteers were tested using three different methods of SCM activation: sitting with the head turned away from the test ear (SIT), supine with the head held straight up (SHU), and supine with the head held up and turned away from the test ear (SHT). Dependent measures were latency, and amplitude. Head and body position significantly affected the amplitude of the VEMP, but had no significant effect on latency. Testing subjects in the supine position with the head up and turned toward the non-test ear yielded the most robust amplitude response and sternocleidomastoid EMG activity. When amplitude measures where corrected according to tonic electromyographic (EMG) activity no significant difference was noted between the three different test positions. The increased amplitude in the supine with head turned position can be directly attributed to increased tonic SCM EMG activity.

Effects of Bone Oscillator Coupling Method, Placement Location, and Occlusion on Bone-Conduction Auditory Steady-State Responses in Infants

The aim of these experiments was to investigate procedures used when estimating bone-conduction thresholds in infants. The objectives were: (i) to investigate the variability in force applied using two common bone-oscillator coupling methods and to determine whether coupling method affects threshold estimation, (ii) to examine effects of bone-oscillator placement on bone-conduction ASSR thresholds, and (iii) to determine whether the occlusion effect is present in infants by comparing bone-conduction ASSR thresholds for unoccluded and occluded ears. Experiment 1A: The variability in the amount of force applied to the bone oscillator by trained assistants (n = 4) for elastic-band and hand-held coupling methods was measured. Experiment 1B: Bone-conduction behavioral thresholds in 10 adults were compared for two coupling methods. Experiment 1C: ASSR thresholds and amplitudes to multiple bone-conduction stimuli were compared in 10 infants (mean age: 17 wk) using two coupling methods. Experiment 2: Bone-conduction ASSR thresholds and amplitudes were compared for temporal, mastoid and forehead oscillator placements in 15 preterm infants (mean age: 35 wk postconceptual age (PCA)). Experiment 3: Bone-conduction ASSR thresholds, amplitudes and phase delays were compared in 13 infants (mean age: 15 wk) for an unoccluded and occluded test ear. All infants that participated had passed a hearing screening test. Experiment 1A: Coupling method did not significantly affect the variability in force applied to the oscillator. Experiment 1B: There were no differences in adult bone-conduction behavioural thresholds between coupling methods. Experiment 1C: There was no significant difference between oscillator coupling method or significant frequency x coupling method interaction for ASSR thresholds or amplitudes in the young infants tested. However, there was a nonsignificant 9-dB better threshold at 4000 Hz for the elastic-band method. Experiment 2: Mean bone-conduction ASSR thresholds for the preterm infants were not significantly different for the temporal and mastoid placements. Mean ASSR thresholds for the forehead placement were significantly higher compared to the other two placements (12-18 dB higher on average). Mean ASSR amplitudes were significantly larger for the temporal and mastoid placements compared to the forehead placement. Experiment 3: There was no difference in mean ASSR thresholds, amplitudes or phase delays for the unoccluded versus occluded conditions. Trained assistants can apply an appropriate amount of force to the bone oscillator using either the elastic-band or hand-held method. Coupling method has no significant effect on estimation of bone-conduction thresholds; therefore, either may be used clinically provided assistants are appropriately trained. For preterm infants, there are no differences in ASSRs when the oscillator is positioned at the temporal or mastoid placement. However, thresholds are higher and amplitudes are smaller for the forehead placement, consequently, a forehead placement should be avoided for clinical testing. There does not appear to be a significant occlusion effect in young infants; therefore, it may be possible to do bone-conduction testing with ears unoccluded or occluded without applying a correction factor, although further research is needed to confirm this finding.

Olivocochlear Efferents: Anatomy, Physiology, Function, and the Measurement of Efferent Effects in Humans

This review covers the basic anatomy and physiology of the olivocochlear reflexes and the use of otoacoustic emissions (OAEs) in humans to monitor the effects of one group, the medial olivocochlear (MOC) efferents. MOC fibers synapse on outer hair cells (OHCs), and activation of these fibers inhibits basilar membrane responses to low-level sounds. This MOC-induced decrease in the gain of the cochlear amplifier is reflected in changes in OAEs. Any OAE can be used to monitor MOC effects on the cochlear amplifier. Each OAE type has its own advantages and disadvantages. The most straightforward technique for monitoring MOC effects is to elicit MOC activity with an elicitor sound contralateral to the OAE test ear. MOC effects can also be monitored using an ipsilateral elicitor of MOC activity, but the ipsilateral elicitor brings additional problems caused by suppression and cochlear slow intrinsic effects. To measure MOC effects accurately, one must ensure that there are no middle-ear-muscle contractions. Although standard clinical middle-ear-muscle tests are not adequate for this, adequate tests can usually be done with OAE-measuring instruments. An additional complication is that most probe sounds also elicit MOC activity, although this does not prevent the probe from showing MOC effects elicited by contralateral sound. A variety of data indicate that MOC efferents help to reduce acoustic trauma and lessen the masking of transients by background noise; for instance, they aid in speech comprehension in noise. However, much remains to be learned about the role of efferents in auditory function. Monitoring MOC effects in humans using OAEs should continue to provide valuable insights into the role of MOC efferents and may also provide clinical benefits.

Enzymatic Recontouring of Auricular Cartilage in a Rabbit Model

To evaluate the effectiveness of contouring auricular cartilage in a rabbit model using biologically active enzymes injected subcutaneously. The first phase determined the most effective volume and concentration required to affect the cartilage. To accomplish this task, we used ex vivo rabbit ears from a slaughterhouse. In the second phase, we injected 1 mL of hyaluronidase (150 U per milliliter of isotonic sodium chloride solution [saline]), elastase (1 mg per milliliter of saline), or saline into the ears of live rabbits. The study took place at the Madigan Army Medical Center (Tacoma, Wash), and included 10 animals. In each rabbit, we injected the test compound in one ear and saline in the other ear (control). We injected hyaluronidase in 5 ears and elastase in 5 ears. After injection, the ears were contoured and splinted for 4 weeks. In the third phase, we changed the injection pathway in 5 animals. At 4 weeks, 4 (80%) of the 5 ears injected with hyaluronidase showed full response and 1 (20%) had a partial response. Of the 5 ears injected with elastase, 4 (80%) showed a full response while 1 (20%) demonstrated a partial response. There was a response in all 10 of the ears injected with a test compound. Of the 10 control ears, 3 (30%) showed a partial response. At 6 weeks, approximately 6 (30%) of the ears had maintained contour demonstrating a full response. The difference between the test ears and the control ears was statistically significant (P = .006). Compared with the control ears, the results were statistically significant for elastase (P = .004) and hyaluronidase (P = .02). Overall, both agents demonstrated a subjective and objective response compared with control ears. This study demonstrates that bioactive enzymes and splinting can be effective in correcting ear deformities in a rabbit model.

Is cochlear outer hair cell function affected by mobile telephone radiation?

Mobile telephones emit high-frequency pulsed electromagnetic fields (PEMF). These are known to have measurable biological effects, and possible effects on the auditory system. Otoacoustic emissions give an indication of the functional state of the auditory system. Otoacoustics are known to be highly specific for the individual when the test pulse is identical. In this way, subtle changes in the ear can be detected. We investigated whether there is a measurable effect on Otoacoustic emissions from PEMF radiation. A total of 12 volunteers were recruited who had normal hearing; confirmed by pure tone audiometry. An Otoacoustic emission trace was obtained. The test subjects were exposed to a mobile telephone that was placed over the test ears mastoid process. The subjects had Otoacoustic emissions measured without the telephone and again on receive and transmit. There was no change in the trace signature during the test. There was no statistically significant change in the trace figures. This would indicate that PEMF from commonly available hand held mobile telephones have no measurable effect on the outer hair cell function during the time of use.

The kinetics and toxicity of leupeptin in the inner ear of the chinchilla

Problem: One strategy to prevent injury to the inner ear after loud noise exposure or other toxic insults is to arrest the neurochemical pathway leading to inner hair cell apoptosis. Leupeptin is a novel antagonist of calpain, a described component of the damage pathway. We desired to evaluate the safety and kinetics of leupeptin in an animal model. Methods: Using a novel surgical approach, we placed middle ear microwicks in 23 chinchillas. The wicks were saturated with a standard amount and concentration of leupeptin and were left in place for 1 of 4 time periods (4 hours, 24 hours, 72 hours, and 7 days.) Additionally, 2 control animals underwent placement of saline-soaked microwicks for 7 days. All animals underwent either air- or bone-conducted preoperative auditory brainstem response (ABR) testing. At the end of the appropriate time period, the contralateral inner ear was surgically ablated and the animals underwent ABR of the test ear. Bilateral perilymph and peripheral blood samples were collected from all animals for evaluation of leupeptin concentration by mass spectrometry. Results: Two animals died during the perioperative period, and 1 animal was excluded because of technical errors. The remaining 20 test animals were distributed among the time points as follows: 4 hr × 4; 24 hr × 5; 72 hr × 5; 7 day × 6. One animal demonstrated hearing loss at 24 hours, 1 at 72 hours, and 1 at 7 days; 2 additional animals at the 7-day time point were deaf on post-exposure testing. Neither of the 7-day saline-control animals demonstrated significant hearing loss. The kinetics of leupeptin will be reviewed. Conclusion: Leupeptin may cause hearing loss in chinchillas. Significance: Inhibitors of damage pathways have great clinical promise in treating acute toxic injuries to the inner ear, but Leupeptin warrants further research in animal models to establish its safety. Support: None reported.

Uncertainty and confusion in temporal masking

In a landmark study, Wright et al. [Nature 387, 176–178 (1997)] reported an apparent backward-masking deficit in language-impaired children. Subsequently, these controversial results have been influential in guiding treatments for childhood language problems. In this study we revisited Wright et al.’s temporal-masking paradigm to evaluate listener uncertainty effects. Masked detection was measured for 20-ms sinusoids (480, 1000, or 1680 Hz) presented at temporal positions before, during, or after a gated narrowband (W=600–1400 Hz) masker. Listener uncertainty was investigated by cueing various stimulus temporal properties with a 6000-Hz sinusoid presented either ipsi- or contra-lateral to the test ear or bilaterally. The primary cueing effect was measured in the backward-masking condition for a contralateral cue gated simultaneously with the on-frequency 1000-Hz signal. The resulting cued masked-detection threshold was reduced to quiet threshold. No significant cueing effects were obtained for other signal temporal positions in the masker nor for any off-frequency signal conditions. These results indicate that (1) uncertainty can be reduced or eliminated for on-frequency backward masking by cueing the signal and (2) the deficit reported by Wright et al. for language-impaired children may reflect uncertainty and confusion rather than a temporal-processing deficit per se. [Research supported by NIDCD.]

Vestibulo-ocular arreflexia in families with spinocerebellar ataxia type 3 (Machado-Joseph disease)

Objective: To identify the presence of vestibulo-ocular arreflexia in patients with Machado-Joseph disease (MJD), which can easily be diagnosed at the bedside. Methods: Seven patients with MJD from five unrelated...

Role of mannitol in reducing postischemic changes in distortion-product otoacoustic emissions (DPOAEs): a rabbit model.

The aim of this study was to observe the effects of mannitol, administered topically at the round window (RW), on cochlear blood flow (CBF) and distortion-product otoacoustic emission (DPOAE) after repeated episodes of cochlear ischemia. Ten young rabbits were used for this study. Reversible ischemic episodes within the cochlea were induced by directly compressing the internal auditory artery (IAA). CBF was measured using a laser-Doppler (LD) probe positioned at the RW niche. DPOAEs were measured at 4, 8, and 12 kHz geometric mean frequency (GMF) using 60 dB sound pressure level (SPL) primary tone stimuli. In five test ears, mannitol was administered topically at the RW for 30 minutes before the IAA compressions. In five control ears, the IAA compressions were undertaken without application of RW medication. Each ear underwent three 5 minute IAA compressions with a 60 minute rest period between compressions. In the control animals, it was observed that a progressive reduction in DPOAE level followed each successive IAA compression at all three test frequencies. The reduction in DPOAE amplitudes was consistently greater at the higher test frequencies. In the test rabbits, the RW administration of mannitol resulted in significantly less reduction in DPOAE level measures after repeated IAA compressions. For example, 30 minutes after reperfusion at 12 kHz GMF, DPOAE levels in the control ears were reduced by 1.5, 6.0, and 16 dB, compared with 1.5, 4.0, and 6.0 dB in the mannitol test ears. Mannitol appears to exert a protective effect on cochlear function after periods of ischemia. The RW appears to be an efficacious route for topical administration of mannitol into the inner ear.

Rapid adaptation of the 2 f1– f2 DPOAE in humans: Binaural and contralateral stimulation effects

The present data were collected in humans to characterize the effects of monaural and binaural stimulation and contralateral noise on the 2 f 1– f 2 distortion-product otoacoustic emission (DPOAE) adaptation response. DPOAE levels ( f 2/ f 1=1.21, L 1=70 dB SPL, L 2=65 dB SPL) were measured in both ears for a range of f 2 frequencies (1.2 to 10.0 kHz). The f 2 frequency producing the largest amplitude DPOAE was used for further testing employing three different stimulus conditions: the primary tones were presented to only one ear for 4 s; the two tones were presented simultaneously in both ears; and, contralateral broadband noise (60 dB SPL) was presented for 5 s, beginning 4 s after the onset of the monaural primaries in the test ear. Acoustic reflex thresholds were measured to verify that the middle-ear muscles played no systematic role in the measured DPOAE reductions. Estimates of monaural rapid adaptation levels and time constants agreed well with previous human findings. The magnitude of the rapid adaptation under binaural stimulation, as compared with monaural primaries, was 25% greater on average, though adaptation time constants were comparable. With added contralateral noise, the average DPOAE suppression was 1.1 dB (0.3–2.7 dB). The magnitude of the monaural adaptation and the effects of binaural and contralateral stimulation, however, were smaller than those measured previously in experimental animals, though the time constants were in good agreement.

Prediction of Non-Linear Amplification Using Different Loudness Scaling Tests

Frequency-specific loudness data are widely used in procedures for fitting non-linear hearing aids, with each procedure using different methods to obtain information about a person's loudness perception. There has been some suggestion that due to differences in methodology different loudness tests result in different prediction of the non-linear amplification when applied according to the same fitting rationale. However, this has not been empirically verified. In this paper the inverse compression ratios prescribed based on a pure loudness normalisation technique and loudness data measured with two different categorical loudness scaling tests were compared for 20 test ears. The data showed that the two loudness tests produced significantly different prescriptions for non-linear amplification and that the discrepancy in prescription was non-linearly related to hearing threshold level with the greatest discrepancy found for cases with moderate loss. Differences in methodology used to obtain the loudness data are argued to be the most likely reason for the measured discrepancy in prescription. Up to 50% of a large variability in data across hearing threshold levels was explained by individual participant factors, suggesting that the interpretation of the two loudness tests varied across participants. The results imply that any fitting rationale based on frequency-specific loudness data is only valid for the test conditions in which the loudness data are obtained, and a hearing aid fitting based on frequency-specific loudness data should be verified.

Effect of Ipsilateral and Contralateral Low-frequency Narrow-band Noise on Temporary Threshold Shift in Humans

Objective – To evaluate the effect of ipsilateral and contralateral low-frequency (250 Hz) narrow-band noise (NBN) on the temporary threshold shift (TTS) induced by a 2 kHz tone in young normally hearing subjects with a functioning auditory efferent system.Material and Methods – Sixteen young volunteers served as subjects. All the subjects were young (20–30 years), disease-free and had a medical history negative for otological disease, noise exposure and use of ototoxic drugs. They had normal hearing [thresholds of 125–8000 Hz below 20 dB hearing level (HL)], transient-evoked otoacoustic emissions and contralateral suppression. The subjects were randomly assigned to one of three different groups. Subjects in Group A (n=5) were exposed to a 90 dB HL 2 kHz pure tone for 10 min. Subjects in Group B (n=6) were exposed to a 90 dB HL 2 kHz pure tone and an ipsilateral 45 dB HL 250 Hz NBN for 10 min. Subjects in Group C (n=5) were exposed to a 90 dB HL 2 kHz pure tone and a contralateral 45 dB HL 250 Hz NBN for 10 min. The right ear served as the test ear. The TTS 2 min after the end of the exposure (TTS2) was measured in all subjects at 2, 3 and 4 kHz.Results – TTS2 in Group A was significantly higher at 3 kHz (p=0.011) and at 4 kHz (p=0.003) than TTS2 in Group B. At 4 kHz, TTS2 in Group C was significantly higher (p=0.013) than TTS2 in Group B. Although TTS2 in Group C was lower than TTS2 in Group A, this difference was not significant. The presence of an ipsilateral low-frequency NBN significantly reduced TTS2 induced by a 90 dB HL 2 kHz tone. A contralateral low-frequency NBN reduced TTS2 in this group of subjects; however, the reduction was not significant.Conclusion – The results of this study show that an ipsilateral low-intensity, low-frequency (250 Hz) NBN can give protection from a TTS induced by a 2 kHz tone. Contralateral low-frequency NBN did not induce any protective effect.

Adaptive apparatus and method for testing auditory sensitivity

A method of testing hearing automatically selects test ear and test frequencies to produce a diagnostic audiogram providing a plurality of quantitative, examiner-independent measures of test reliability. The method automatically presents appropriate masking noise to a non-test ear. In addition, the method alerts an examiner to thresholds that may be inaccurate due to inappropriate masking or subject inconsistency. A software driven system automatically carries out the method on a test subject.