Linda W. Norrix

The auditory brainstem response: latencies obtained in children while under general anesthesia.

BACKGROUND The auditory brainstem response (ABR) test is frequently employed to estimate hearing sensitivity and assess the integrity of the ascending auditory system. In persons who cannot participate in conventional tests of hearing, a short-acting general anesthetic is used, recordings are obtained, and the results are compared with normative data. However, several factors (e.g., anesthesia, temperature changes) can contribute to delayed absolute and interpeak latencies, making it difficult to evaluate the integrity of the persons auditory brainstem function. PURPOSE In this study, we investigated the latencies of ABR responses in children who received general anesthesia. RESEARCH DESIGN Between subject. STUDY SAMPLE Twelve children between the ages of 29 and 52 mo, most of whom exhibited a developmental delay but normal peripheral auditory function, comprised the anesthesia group. Twelve participants between the ages of 13 and 26 yr with normal hearing thresholds comprised the control group. DATA COLLECTION AND ANALYSIS ABRs from a single ear from children, recorded under general anesthesia, were retrospectively analyzed and compared to those obtained from a control group with no anesthesia. ABRs were generated using 80 dB nHL rarefaction click stimuli. T-tests, corrected for alpha slippage, were employed to examine latency differences between groups. RESULTS There were significant delays in latencies for children evaluated under general anesthesia compared to the control group. Delays were observed for wave V and the interpeak intervals I-III, III-V, and I-V. CONCLUSIONS Our data suggest that caution is needed in interpreting neural function from ABR data recorded while a child is under general anesthesia.

Auditory Neuropathy Spectrum Disorder: A Review

PURPOSE Auditory neuropathy spectrum disorder, or ANSD, can be a confusing diagnosis to physicians, clinicians, those diagnosed, and parents of children diagnosed with the condition. The purpose of this review is to provide the reader with an understanding of the disorder, the limitations in current tools to determine site(s) of lesion, and management techniques. METHOD This article is a review of what is known about ANSD. It includes descriptions of assessment tools, causes of ANSD, and patient management techniques. CONCLUSIONS This review is a guide to audiologists, speech-language pathologists, and early interventionists who work with individuals diagnosed with ANSD and/or their families. It highlights the need for more precise tools to describe the disorder in order to facilitate decisions about interventions and lead to better predictions of outcome.

Measuring the Advantage of Kalman-Weighted Averaging for Auditory Brainstem Response Hearing Evaluation in Infants

PURPOSE The purposes of this study were to (a) measure the effects of Kalman-weighted averaging methods on auditory brainstem response (ABR) threshold, latency, and amplitude; (b) translate lab findings to the clinical setting; and (c) estimate cost savings when ABRs can be obtained in nonsedated infants. METHOD ABRs were recorded in 40 adults with normal hearing during induced motor noise conditions using the Kalman-weighted averaging method implemented on a commercial system, the Vivosonic Integrity (Vivosonic Inc., Toronto, Ontario, Canada). The device was then used to test 34 infants in awake and asleep states. The advantages of the Kalman-weighted averaging method were modeled in terms of time saved for conducting an ABR evaluation. RESULTS Kalman-weighted ABR threshold estimates were 6-7 dB lower than with conventional methods during induced motor noise. When used to obtain ABRs in infants who were awake, the number of sweeps required to obtain a result was significantly greater than that required for a sleeping infant but well within the range for clinical application. CONCLUSIONS The use of Kalman-weighted averaging provides a measurable advantage over conventional methods and may reduce costs for the pediatric audiology practice.

Auditory‐visual context effects on the perception of /r/ and /l/ in a stop cluster.

Context effects in speech perception are thought to reflect knowledge about coarticulatory influences from the surrounding phonetic environment. This study investigated if such effects occur when the context is specified in the visual modality and segmental information in the auditory modality. In the first experiment, two continua were synthesized: one varying from /iri–ili/ and the other from /ibri–ibli/. When presented to listeners for identification as /r/ or /l/, there was a significant shift in the category boundary between the two continua. In a second experiment, the /iri–ili/ tokens were paired with visual tokens of a talker saying /ibi/. When presented in an auditory‐visual (AV) condition, these tokens were perceived as ranging from /ibri/ to /ibli/. Observers also identified the /iri–ili/ tokens in a separate auditory‐only (AO) condition. Results indicated a similar shift in the /r–l/ boundary between the AO and AV conditions. Analysis of /r/ and /l/ productions revealed that the perceptual adj...

DISTORTION PRODUCT OTOACOUSTIC EMISSIONS CREATED THROUGH THE INTERACTION OF SPONTANEOUS OTOACOUSTIC EMISSIONS AND EXTERNALLY GENERATED TONES

An SOAE (f2) and one XT (f1) were used to create 2 f1−f2 DPOAEs. External tones were applied to the ear canal at SOAE/f1 ratios between 1.08 and 1.22 XT/SOAE intensity differences varied from 0 to approximately 50 dB SPL. DPOAE amplitude and SOAE suppression characteristics were variable across subjects. However, the following trends were noted: (1) At larger frequency ratios, DPOAE generation and SOAE suppression were associated with greater XT SPLs; (2) DPOAE growth functions were characterized by slopes <1 dB/dB, a maximum, rollover and disappearance into the noise floor; (3) maximum DPOAEs were observed at frequencies approximately 1/2 oct below the SOAEs; (4) DPOAE maximums were associated with a significant amount of SOAE suppression. The results are consistent with DPOAEs created using two low‐level tones [Brown and Gaskill, in Mechanics and Biophysics of Hearing (Springer‐Verlag, Berlin, 1990)] and can be interpreted by considering suppression in a nonlinear cochlear model [Zwicker, 163–176 (1986)...

Conductive Hearing Loss in Bighorn Sheep

In January 1993 we simulated a conductive hearing loss in three Mexican bighorn sheep (Ovis canadensis mexicana) by placing bone wax or saline solution in their ear canals. Our objective was to test whether lesions of the external auditory canal caused by psoroptic mites (Psoroptes ovis) may lead to conductive hearing loss in bighorn sheep. We assessed the effects of these manipulations using the auditory brainstem response test. Placing saline solution in the external auditory canal, which loads the tympanic membrane, had a more dramatic effect on the auditory brainstem response than did bone wax. We propose that decreased hearing sensitivity or alterations in resonance characteristics of the external auditory canal, due to psoroptic scabies lesions, may make bighorn sheep more susceptible to predation.

Multichannel waveforms and topographic mapping of the auditory brainstem response under common stimulus and recording conditions

Topographic representation of brain electrical activity may be employed to provide information about excitation patterns and symmetry of responses to sensory stimulation. The present investigation describes the waveforms and topographic distribution of the auditory brainstem response (ABR) in normal-hearing and neurologically-normal women during several stimulus and recording conditions using a multiple electrode array. Acoustic stimuli were rarefaction clicks presented monaurally at five intensities. Latencies and amplitudes for the sagittal and coronal electrodes as well as the topographies of waves I, III, and V were described. Wave I, in an ipsilateral inverting reference condition, exhibited smallest amplitudes at the temporal electrode ipsilateral to the stimulated ear and maximum voltage at electrode sites contralateral to the stimulated ear. Amplitude and latency patterns of wave III were peculiar to level of stimulation, ear of stimulation and selection of inverting electrode site. Wave III maximum voltage was detected at fronto-central scalp areas contralateral to the stimulated ear. Wave V latencies and amplitudes varied across electrode site and inverting electrode position. Its topography revealed maximum positive voltage at fronto-central electrodes, slightly asymmetric in some instances. Analysis of amplitude and topographic patterns of ABR components may provide useful information to supplement that provided by conventional displays of waveforms.

Unraveling the mystery of auditory brainstem response corrections: The need for universal standards

Background: The auditory brainstem response (ABR) is used to estimate behavioral hearing thresholds in infants and difficult‐to‐test populations. Differences between the toneburst ABR and behavioral thresholds exist making the correspondence between the two measures less than perfect. Some authors have suggested that corrections be applied to ABR thresholds to account for these differences. However, because there is no agreed upon universal standard, confusion regarding the use of corrections exists. Purpose: The primary purpose of this article is to review the reasoning behind and use of corrections when the toneburst ABR is employed to estimate behavioral hearing thresholds. We also discuss other considerations that all audiologists should be aware of when obtaining and reporting ABR test results. Results: A review of the purpose and use of corrections reveals no consensus as to whether they should be applied or which should be used. Additionally, when ABR results are adjusted, there is no agreement as to whether additional corrections for hearing loss or the age of the client are necessary. This lack of consensus can be confusing for all individuals working with hearing‐impaired children and their families. Conclusions: Toneburst ABR thresholds do not perfectly align with behavioral hearing thresholds. Universal protocols for the use of corrections are needed. Additionally, evidence‐based procedures must be employed to obtain valid ABRs that will accurately estimate hearing thresholds.

Estimating Nonorganic Hearing Thresholds Using Binaural Auditory Stimuli

Purpose Minimum contralateral interference levels (MCILs) are used to estimate true hearing thresholds in individuals with unilateral nonorganic hearing loss. In this study, we determined MCILs and examined the correspondence of MCILs to true hearing thresholds to quantify the accuracy of this procedure. Method Sixteen adults with normal hearing participated. Subjects were asked to feign a unilateral hearing loss at 1.0, 2.0, and 4.0 kHz. MCILs were determined. Subjects also made lateralization judgments for simultaneously presented tones with varying interaural intensity differences. Results The 90% confidence intervals, calculated for the distributions, indicate that the MCIL in 90% of cases would be expected to be very close to threshold to approximately 17-19 dB poorer than the true hearing threshold. How close the MCIL is to true threshold appears to be based on the individuals response criterion. Conclusions Response bias influences the MCIL and how close an MCIL is to true hearing threshold. The clinician can never know a clients response bias and therefore should use a 90% confidence interval to predict the range for the expected true threshold. On the basis of this approach, a clinician may assume that true threshold is at or as much as 19 dB better than MCIL.

Audiometric Thresholds: Stimulus Considerations in Sound Field and Under Earphones

PURPOSE This study evaluates a new stimulus, FREquency Specific Hearing assessment (FRESH) noise, to obtain hearing thresholds and reviews the potential pitfalls of using narrow band noise. METHOD Twelve adults with simulated gradually sloping hearing loss and 12 adults with steeply sloping hearing loss participated. Hearing thresholds were measured in sound field and under a supraaural earphone for FRESH noise, warbled tones, and narrowband noise. Pure-tone thresholds were also measured under the supraaural earphone. RESULTS FRESH noise thresholds were similar to pure-tone and warbled-tone thresholds regardless of audiometric configuration. For the group with gradually sloping hearing loss, thresholds obtained with narrowband noise were approximately 4 dB better than those obtained with the other test stimuli. For the group with steeply sloping hearing loss, narrowband noise significantly underestimated hearing thresholds-the steeper the hearing loss, the greater the underestimation. CONCLUSIONS When hearing loss is suspected, FRESH noise is appropriate for accurately determining audiometric thresholds in sound field and under earphones. A wider band, attention-getting stimulus such as narrowband noise can result in thresholds that are inaccurate. Clinical decision making regarding choice of test stimulus is discussed.