Wideband acoustic immittance measurements of the middle ear: introduction and some historical antecedents.

This supplement focuses on some of the most recent acoustic measurements within the occluded, human external auditory meatus (EAM). The goal of this introduction is to provide an overview of basic and clinical EAM measurements that evolved in the 20th century and some relations between these measurements and wideband acoustic absorbance. The authors review some of the major efforts that have been used to evaluate the condition of the human, adult middle ear transmission system, the middle ear cavity, and the function of the Eustachian tube. They have grouped most of this work under the rubric of "acoustic immittance." A historical perspective helps one appreciate that the measurement of wideband acoustic absorbance is not a totally new procedure. Rather, it is the latest enhancement to aural acoustic-immittance measurements. An enhancement that can expand one's ability to characterize middle ear function and effects of ear disease on that function. It also allows clinicians evaluate middle ear function for frequencies whose wavelength is shorter than the length of the EAM.

Consensus statement: Eriksholm workshop on wideband absorbance measures of the middle ear.

The participants in the Eriksholm Workshop on Wideband Absorbance Measures of the Middle Ear developed statements for this consensus article on the final morning of the Workshop. The presentations of the first 2 days of the Workshop motivated the discussion on that day. The article is divided into three general areas: terminology; research needs; and clinical application. The varied terminology in the area was seen as potentially confusing, and there was consensus on adopting an organizational structure that grouped the family of measures into the term wideband acoustic immittance (WAI), and dropped the term transmittance in favor of absorbance. There is clearly still a need to conduct research on WAI measurements. Several areas of research were emphasized, including the establishment of a greater WAI normative database, especially developmental norms, and more data on a variety of disorders; increased research on the temporal aspects of WAI; and methods to ensure the validity of test data. The area of clinical application will require training of clinicians in WAI technology. The clinical implementation of WAI would be facilitated by developing feature detectors for various pathologies that, for example, might combine data across ear-canal pressures or probe frequencies.

Development of a "virtual cocktail party" for the measurement of speech intelligibility in a sound field.

This technical report describes an approach to the measurement of speech intelligibility for sentences presented in a sound field in the presence of 16-talker babble. More specifically, we detail our (1) selection and preparation of target speech materials, (2) selection and preparation of experimental babble, (3) analog instrumentation, (4) software routines for attenuator control, (5) calibration, (6) experimental subjects, and (7) experimental protocol. In the final section of this report we present speech-intelligibility data from 16 young adults (21-30 yr of age) with normal hearing sensitivity for pure-tone signals.

Frequency-modulation (FM) technology as a method for improving speech perception in noise for individuals with multiple sclerosis.

Almost half of the population with multiple sclerosis (MS) complains of difficulty hearing, despite having essentially normal pure-tone thresholds. The purpose of the present investigation was to evaluate the effects of frequency-modulation (FM) technology utilization on speech perception in noise for adults with and without MS. Sentence material was presented at a constant level of 65 dBA Leq from a loudspeaker located at 0 degrees azimuth. The microphone of the FM transmitter was placed 7.5 cm from this loudspeaker. Multitalker babble was presented from four loudspeakers positioned at 45 degrees, 135 degrees, 225 degrees, and 315 degrees azimuths. The starting presentation level for the babble was 55 dBA Leq, The level of the noise was increased systematically in 1 dB steps until the subject obtained 0% key words correct on the IEEE (Institute for Electrical and Electronic Engineers) sentences. Test results revealed significant differences between the unaided and aided conditions at several signal-to-noise ratios.

Cochlear delays measured with amplitude-modulated tone-burst-evoked OAEs.

Delay times in the mammalian cochlea, whether from measurement of basilar membrane (BM) vibration or otoacoustic emissions (OAEs) have, to date, been largely based on phase-gradient estimates from steady-state responses. Here we report cochlear delays measured directly in the time domain from OAEs evoked by amplitude-modulated tone-burst (AMTB) stimuli. Measurement using OAEs provides a non-invasive estimate of cochlear delay but is confounded by the complexity of generation of such OAEs. At low to moderate stimulus levels, and provided that the stimulus frequency range does not include a region of the cochlea where there is a large change in effective reflectance, AMTB stimuli evoke an OAE with an envelope shape that is similar to the stimulus and allow a direct calculation of cochlear group delay. Such delays are commensurate with BM estimates of delay, estimates of cochlear delay inferred from neural recordings, and previous OAE measures of delay in the guinea pig. However, a nonlinear distortion mechanism, variation in effective reflectance, and intermodulation distortion products generated by the nonlinear interaction in the cochlea of the carrier and sidebands of the AMTB stimulus, may all contribute to OAEs arising with envelope shapes that are not a scaled representation of the stimulus, confounding the estimation of cochlear group delay.

Tympanometric findings in patients with enlarged vestibular aqueducts.

OBJECTIVES: The purpose of this study was to study systematically some relationships between the resonance frequency of the middle-ear transmission system and the volume of the endolymphatic duct and sac in patients with an enlarged vestibular aqueduct (EVA). STUDY DESIGN: Prospective study. METHODS: Thirteen patients (24 ears) with EVA, 17 subjects (29 ears) with normal hearing, and 17 patients (21 ears) with sensorineural hearing loss without EVA served as experimental subjects. Standard pure-tone audiometry, standard clinical tympanometry (using a 226-Hz probe tone), and multifrequency tympanometry were performed on each ear. Magnetic resonance imaging was used to determine the area of the cochlear modiolus and the volume of the endolymphatic duct and sac. RESULTS: The audiometric configurations for most patients sloped downward from the low to the high frequencies. A significant air-bone gap was computed at each of these test frequencies. Multifrequency tympanometry yielded resonance frequencies for the patients with EVA that was significantly lower than those measured for the control subjects. In general, for patients with EVA, the resonance frequency of the middle ear system decreased as the volume of the endolymphatic duct and sac increased. This inverse relation was significant (correlation coefficient = -0.483, P =.0157). However, there was no correlation between resonance frequency and the degree of cochlea modiolar deficiency. CONCLUSIONS: Clinically, our findings suggest that EVA probably should be included in the differential diagnosis for a patient who presents with a moderate to severe mixed hearing loss, a normal tympanogram at 226 Hz, and a resonance frequency that is abnormally low.

Vibration perception thresholds of human maxillary and mandibular central incisors.

Tactile information from dental mechanoreceptors contributes to the perception of food bolus textures and the control of mastication. While numerous studies have measured the light-touch sensory thresholds of teeth, little information is available about the vibrotactile perception thresholds of teeth. This study uses an adaptive psychophysical procedure to determine thresholds of vibratory stimulation of maxillary and mandibular central incisors in 16 healthy human subjects. An electromechanical vibrator delivered labiolingual forces perpendicular to the long axis of the maxillary and mandibular incisors at 10 stimulation frequencies between 40 and 315 Hz. The median thresholds ranged between 44 and 104 mN. A linear regression analysis revealed a significant increase in the vibrotactile thresholds with increasing frequencies for stimulation of the maxillary and mandibular incisors. No significant differences were found between regression slopes of the thresholds of the maxillary and mandibular incisors. These results indicated that maxillary and mandibular incisors should be able to discriminate effectively among a variety of textures based on their ability to encode a wide range of vibration frequencies.

Does interferon beta-1a impact pure-tone hearing sensitivity among individuals with multiple sclerosis?

BACKGROUND: Previous studies reported that particular types of interferon medications might contribute to hearing loss in some patients. The package insert included in the original Food and Drug Administration application for intramuscular interferon beta-1a (Avonex) stated that some patients in the treatment group reported decreased hearing sensitivity. OBJECTIVE: The purpose of the present investigation was to assess if individuals with multiple sclerosis (MS) taking intramuscular interferon beta-1a have significantly poorer hearing thresholds than those not currently using any disease-modifying therapies. METHODS: This was a secondary analysis of data collected as part of two larger studies evaluating auditory function in patients with MS. The goal of this analysis was to determine if users of interferon beta-1a do not have significantly worse hearing thresholds than nonusers of disease-modifying therapies, after adjusting for potential confounders. A linear mixed model was fit to the audiometric thresholds of our subjects. This model included interferon beta-1a use, MS disease subtype, gender, test frequency, age, disease duration (number of years), and the Expanded Disability Status Scale score. RESULTS AND CONCLUSIONS: With all subjects included, there is insufficient evidence to say that intramuscular interferon-beta 1a is not ototoxic (in relation to nonuse of a disease-modifying therapy) at all frequencies tested except 3000 and 6000 Hz. After removing two influential subjects, the results indicated that there is statistical support for no ototoxic effect of intramuscular interferon beta-1a at test frequencies from 250 to 6000 Hz. There is insufficient evidence, however, to rule out an ototoxic effect at 8000 Hz. Future studies should further evaluate the effect of interferon on auditory function in patients with MS. Neuroscience nurses should monitor their patients' hearing throughout the course of treatment.

Audiometric hearing status of individuals with and without multiple sclerosis.

The purpose of the present investigation was to determine whether differences exist in audiometric hearing status between individuals with and without multiple sclerosis (MS) and between individuals with relapsing-remitting MS (RRMS) and individuals with secondary progressive MS (SPMS). Forty-seven subjects with MS (26 with RRMS and 21 with SPMS) and forty-nine control subjects without MS completed both a comprehensive case-history questionnaire and a conventional hearing evaluation. Statistical analyses, accounting for the potential confounding factors of age, sex, noise exposure, and use of ototoxic medications, revealed significant differences in hearing thresholds between subjects with and without MS at select audiometric test frequencies (p < 0.05). At these audiometric test frequencies, the subjects with MS had poorer hearing thresholds. Additional analyses revealed significant differences in hearing sensitivity at select audiometric frequencies between the subjects with RRMS and the subjects with SPMS, such that those with SPMS had poorer hearing thresholds. These findings have significant clinical implications for practitioners working with patients with MS.

Some effects of multiple sclerosis on speech perception in noise: Preliminary findings.

The present investigation examined speech perception in noise of adults with and without multiple sclerosis (MS). Institute of Electrical and Electronic Engineers (IEEE) sentences were presented at a constant level of 65 dBA L(eq) (equivalent continuous noise level [4 dB exchange rate]) from a loudspeaker located at 0-degree horizontal azimuth and 1.2 m from the study participant. Uncorrelated multitalker babble was presented from four loudspeakers positioned at 45-, 135-, 225-, and 315-degree azimuths and 1.7 m from the study participant. The starting presentation level for the babble was 55 dBA L(eq). The level of the babble was increased systematically in 1 dB steps until the subject obtained 0% key words correct on the IEEE sentences. Results revealed a significant difference in speech perception between the two groups at nine signal-to-noise ratios. Some clinical implications of these results are discussed.

What drives mechanical amplification in the mammalian cochlea?

The recent report by Peter Dallos and colleagues of the gene and protein responsible for outer hair cell somatic motility (Zheng, Shen, He, Long, Madison, & Dallos, 2000), and the work of James Hudspeth and colleagues demonstrating that vestibular stereocilia are capable of providing power that may boost the vibration of structures within the inner ear (Martin & Hudspeth, 1999), presents the tantalizing possibility that we may not be far away from answering the question what drives mechanical amplification in the mammalian cochlea? This article reviews the evidence for and against each of somatic motility as the motor, and a motor in the hair cell bundle, producing cochlear mechanical amplification. We consider three models based on somatic motility as the motor and two based on a motor in the hair cell bundle. Available evidence supports a hair cell bundle motor in nonmammals but the upper frequency limit of mammalian hearing in general exceeds that of nonmammals, in many cases by an order of magnitude or more. Only time will tell whether an evolutionary dichotomy exists (Manley, Kirk, Köppl, & Yates, 2001).

Sources and mechanisms of DPOAE generation: implications for the prediction of auditory sensitivity.

Otoacoustic emissions (OAEs) have become a commonly used clinical tool for assessing cochlear health status, in particular, the integrity of the cochlear amplifier or motor component of cochlear function. Predicting hearing thresholds from OAEs, however, remains a research challenge. Models and experimental data suggest that there are two mechanisms involved in the generation of OAEs. For distortion product, transient, and high-level stimulus frequency emissions, the interaction of multiple sources of emissions in the cochlea leads to amplitude variation in the composite ear canal signal. Multiple sources of emissions complicate simple correlations between audiometric test frequencies and otoacoustic emission frequencies. Current research offers new methods for estimating the individual components of OAE generation. Input-output functions and DP-grams of the nonlinear component of the 2f2-f2 DPOAE may ultimately show better correlations with hearing thresholds. This paper reviews models of OAE generation and methods for estimating the contribution of source components to the composite emission that is recorded in the ear canal. The clinical implications of multiple source components are discussed.