Prenatal Exposure to Tobacco and Alcohol Alters Development of the Neonatal Auditory System.

Prenatal exposures to alcohol (PAE) and tobacco (PTE) are known to produce adverse neonatal and childhood outcomes including damage to the developing auditory system. Knowledge of the timing, extent, and combinations of these exposures on effects on the developing system is limited. As part of the physiological measurements from the Safe Passage Study, Auditory Brainstem Responses (ABRs) and Transient Otoacoustic Emissions (TEOAEs) were acquired on infants at birth and one-month of age. Research sites were in South Africa and the Northern Plains of the U.S. Prenatal information on alcohol and tobacco exposure was gathered prospectively on mother/infant dyads. Cluster analysis was used to characterize three levels of PAE and three levels of PTE. Repeated-measures ANOVAs were conducted for newborn and one-month-old infants for ABR peak latencies and amplitudes and TEOAE levels and signal-to-noise ratios. Analyses controlled for hours of life at test, gestational age at birth, sex, site, and other exposure. Significant main effects of PTE included reduced newborn ABR latencies from both ears. PTE also resulted in a significant reduction of ABR peak amplitudes elicited in infants at 1-month of age. PAE led to a reduction of TEOAE amplitude for 1-month-old infants but only in the left ear. Results indicate that PAE and PTE lead to early disruption of peripheral, brainstem, and cortical development and neuronal pathways of the auditory system, including the olivocochlear pathway.

Protocol for Rapid, Accurate, Electrophysiologic, Auditory Assessment of Infants and Toddlers.

BACKGROUND: Audiologists often lack confidence in results produced by current protocols for diagnostic electrophysiologic testing of infants. This leads to repeat testing appointments and slow protocols which extend the time needed to complete the testing and consequently delay fitting of amplification. A recent publication (Sininger et al50) has shown how new technologies can be applied to electrophysiologic testing systems to improve confidence in results and allow faster test protocols. Average test times for complete audiogram predictions when using new technologies and protocols were found to be just over 32 minutes using auditory brainstem response (ABR) and just under 20 minutes using auditory steady-state response (ASSR) technology. PURPOSE: The purpose of this manuscript is to provide details of expedited test protocols for infant and toddler diagnostic electrophysiologic testing. SUMMARY: Several new technologies and their role in test speed and confidence are described including CE-Chirp stimuli, automated detection of ABRs using a technique called F MP, Bayesian weighting which is an alternative to standard artifact rejection and Next-Generation ASSR with improved response detection and chirp stimuli. The test protocol has the following features: (1) preliminary testing includes impedance measures and otoacoustic emissions, (2) starting test levels are based on Broad-Band CE-Chirp thresholds in each ear, (3) ABRs or ASSRs are considered present based on automated detection rather than on replication of responses, (4) number of test levels is minimized, (5) ASSR generally evaluates four frequencies in each ear simultaneously with flexibility to change all test levels independently. CONCLUSIONS: Combining new technologies with common-sense strategies has been shown to substantially reduce test times for predicting audiometric thresholds in infants and toddlers (Sininger et al50). Details and rationales for changing test strategies and protocols are given and case examples are used to illustrate.

Transient Otoacoustic Emissions and Auditory Brainstem Responses in Low-Risk Cohort of Newborn and One-Month-Old Infants: Assessment of Infant Auditory System Physiology in the Prenatal Alcohol in SIDS and Stillbirth Network Safe Passage Study.

BACKGROUND: The Prenatal Alcohol and Sudden Infant Death Syndrome and Stillbirth Network, known as the "Safe Passage Study," enrolled approximately 12,000 pregnant women from the United States and South Africa and followed the development of their babies through pregnancy and the infant's first year of life to investigate the role of prenatal alcohol exposure in the risk for sudden infant death syndrome (SIDS) and adverse pregnancy outcomes, such as stillbirth and fetal alcohol spectrum disorders. PURPOSE: Auditory system tests were included in the physiologic test battery used to study the effects of prenatal alcohol exposure on neurophysiology and neurodevelopment, as well as potential causal relationships between neurodevelopmental disorders and SIDS and/or stillbirth. The purpose of this manuscript is to describe normative results when using the auditory test battery applied. RESEARCH DESIGN: The test battery included the auditory brainstem response (ABR) and transient-evoked otoacoustic emissions (TEOAEs). Data were collected on individual ears of newborns and 1-month-old infants. STUDY SAMPLE: From a cohort of 6,070 with auditory system exams, a normative subsample of 325 infants were selected who were not exposed prenatally to alcohol, cigarette smoke, or drugs nor were they preterm or low birthweight. The subsample is small relative to the overall study because of strict criteria for no exposure to substances known to be associated with SIDS or stillbirth and the exclusion of preterm and low birthweight infants. Expectant mothers were recruited from general maternity at two comprehensive clinical sites, in the northern plains in the United States and in Cape Town, South Africa. These populations were selected for study because both were known to be at high-risk for SIDS and stillbirth. DATA COLLECTION AND ANALYSIS: ABR and TEOAE recordings were stored electronically. Peak latency and amplitude analysis of ABRs were determined by study personnel, and results were evaluated for differences by age, sex, test site, race, and ear (left versus right). RESULTS: TEOAE findings were consistent with existing literature including the increase in signal-to-noise (SNR) over the first month of life. The SNR increase is due to an increase in amplitude of the emission. TEOAE amplitude asymmetry favoring the right ear was found, whereas SNR asymmetry was not, perhaps because of the small sample size. A nonsignificant trend toward larger responses in female babies was found; a result that is generally statistically significant in studies with larger samples. Latencies were found to be shorter in ABRs elicited in the right ear with amplitudes that were slightly bigger on average. An expected decrease in wave V latency was observed from birth to 1-month of age, but the finding was of borderline significance (p = 0.058). CONCLUSIONS: One month is a short time to judge development of the auditory system; however, the ABR and TEOAE findings were consistent with current literature. We conclude that the auditory system data acquired for the Safe Passage Study, as reflected in the data obtained from this cohort of "unexposed" infants, is consistent with published reports of these auditory system measures in the general population.

Evaluation of Speed and Accuracy of Next-Generation Auditory Steady State Response and Auditory Brainstem Response Audiometry in Children With Normal Hearing and Hearing Loss.

OBJECTIVES: The first objective of this study was to compare the predicted audiometric thresholds obtained by auditory steady state response (ASSR) and auditory brainstem response (ABR) in infants and toddlers when both techniques use optimal stimuli and detection algorithms. This information will aid in determining the basis for large discrepancies in ABR and ASSR measures found in past studies. The hypothesis was that advancements in ASSR response detection would improve (lower) thresholds and decrease discrepancies between the thresholds produced by the two techniques. The second objective was to determine and compare test times required by the two techniques to predict thresholds for both ears at the 4 basic audiometric frequencies of 500, 1000, 2000, and 4000 Hz. DESIGN: A multicenter clinical study was implemented at three university-based children's hospital audiology departments. Participants were 102 infants and toddlers referred to the centers for electrophysiologic testing for audiometric purposes. The test battery included wideband tympanometry, distortion-product otoacoustic emissions, and threshold measurements at four frequencies in both ears using ABR and ASSR (randomized) as implemented on the Interacoustics Eclipse systems with "Next-Generation" ASSR detection and FMP analysis for ABR. Both methods utilized narrow band CE-Chirp stimuli. Testers were trained on a specialized test battery designed to minimize test time for both techniques. Testing with both techniques was performed in one session. Thresholds were evaluated and confirmed by the first author and correction factors were applied. Test times were documented in system software. RESULTS: Corrected thresholds for ABR and ASSR were compared by regression, by the Bland-Altman technique and by matched pairs t tests. Thresholds were significantly lower for ASSR than ABR. The ABR-ASSR discrepancy at 500 Hz was 14.39 dB, at 1000 Hz was 10.12 dB, at 2000 Hz was 3.73 dB, and at 4000 Hz was 3.67 dB. The average test time for ASSR of 19.93 min (for 8 thresholds) was found to be significantly lower (p < 0.001) than the ABR test time of 32.15 min. One half of the subjects were found to have normal hearing. ASSR thresholds plotted in dB nHL for normal-hearing children in this study were found to be the lowest yet described except for one study which used the same technology. CONCLUSIONS: This study found a reversal of previous findings with up to 14 dB lower thresholds found when using the ASSR technique with "Next-Generation" detection as compared with ABR using an automated detection (FMP). The test time for an audiogram prediction was significantly lower when using ASSR than ABR but was excellent by clinical standards for both techniques. ASSRs improved threshold performance was attributed to advancements in response detection including utilization of information at multiple harmonics of the modulation frequency. The stimulation paradigm which utilized narrow band CE-Chirps also contributed to the low absolute levels of the thresholds in nHL found with both techniques.

Deaf genetic testing and psychological well-being in deaf adults.

Limited data suggest that enhanced self-knowledge from genetic information related to non-medical traits can have a positive impact on psychological well-being. Deaf individuals undertake genetic testing for deaf genes to increase self-knowledge. Because deafness is considered a non-medical trait by many individuals, we hypothesized that deaf individuals receiving a genetic explanation for why they are deaf will experience increased psychological well-being. We report results from a prospective, longitudinal study to determine the impact of genetic testing (GJB2, Cx26; GJB6, Cx30) on perceived personal control (PPC), anxiety, and depression in deaf adults (N = 209) assessed following pre-test genetic counseling as well as 1-month and 6-months following test result disclosure. Participants were classified as Cx positive (n = 82) or Cx negative/inconclusive (n = 127). There was significant evidence for Cx group differences in PPC and anxiety over time (PPC: Cx group*time interaction p = 0.0007; anxiety: Cx group*time interaction p = 0.002), where PPC scores were significantly higher, and anxiety scores were significantly lower for the Cx positive group relative to the negative/inconclusive group following test result disclosure. Compared to pre-test, PPC scores increased at 1-month (p = 0.07) and anxiety scores decreased at 6-months (p = 0.03) for the Cx positive group. In contrast, PPC scores decreased (p = 0.009, p < 0.0001) and anxiety scores increased (p = 0.09, p = 0.02) for the Cx negative/inconclusive group at 1- and 6-months post test result disclosure. Genetic testing for deaf genes affects the psychological well-being of deaf individuals. Increasing deaf adults' access to genetic testing may potentially enhance self-knowledge and increase psychological well-being for those who receive a genetic explanation, which could offer downstream health benefits.

Impaired timing and frequency discrimination in high-functioning autism spectrum disorders.

Individuals with autism spectrum disorders (ASD) frequently demonstrate preserved or enhanced frequency perception but impaired timing perception. The present study investigated the processing of spectral and temporal information in 12 adolescents with ASD and 15 age-matched controls. Participants completed two psychoacoustic tasks: one determined frequency difference limens, and the other determined gap detection thresholds. Results showed impaired frequency discrimination at the highest standard frequency in the ASD group but no overall difference between groups. However, when groups were defined by auditory hyper-sensitivity, a group difference arose. For the gap detection task, the ASD group demonstrated elevated thresholds. This supports previous research demonstrating a deficit in ASD in temporal perception and suggests a connection between hyper-sensitivity and frequency discrimination abilities.

Laterality of basic auditory perception.

Laterality (left-right ear differences) of auditory processing was assessed using basic auditory skills: (1) gap detection, (2) frequency discrimination, and (3) intensity discrimination. Stimuli included tones (500, 1000, and 4000 Hz) and wide-band noise presented monaurally to each ear of typical adult listeners. The hypothesis tested was that processing of tonal stimuli would be enhanced by left ear (LE) stimulation and noise by right ear (RE) presentations. To investigate the limits of laterality by (1) spectral width, a narrow-band noise (NBN) of 450-Hz bandwidth was evaluated using intensity discrimination, and (2) stimulus duration, 200, 500, and 1000 ms duration tones were evaluated using frequency discrimination. A left ear advantage (LEA) was demonstrated with tonal stimuli in all experiments, but an expected REA for noise stimuli was not found. The NBN stimulus demonstrated no LEA and was characterised as a noise. No change in laterality was found with changes in stimulus durations. The LEA for tonal stimuli is felt to be due to more direct connections between the left ear and the right auditory cortex, which has been shown to be primary for spectral analysis and tonal processing. The lack of a REA for noise stimuli is unexplained. Sex differences in laterality for noise stimuli were noted but were not statistically significant. This study did establish a subtle but clear pattern of LEA for processing of tonal stimuli.

Deaf adults' reasons for genetic testing depend on cultural affiliation: results from a prospective, longitudinal genetic counseling and testing study.

This article examines the relationship between cultural affiliation and deaf adults' motivations for genetic testing for deafness in the first prospective, longitudinal study to examine the impact of genetic counseling and genetic testing on deaf adults and the deaf community. Participants (n = 256), classified as affiliating with hearing, Deaf, or both communities, rated interest in testing for 21 reasons covering 5 life domains. Findings suggest strong interest in testing to learn why they are deaf, but little interest in using it for decisions about a partner or having children. Culturally mediated variation was also demonstrated. Deaf and both communities groups viewed testing as useful for more life domains than the hearing community group. Deaf and both communities had similar motivations related to further exploration, understanding, or strengthening of deafness. Motivations related to "hearing" were also relevant for both communities. We conclude that cultural affiliation is an important factor for constructing motivations for genetic testing.

Auditory development in early amplified children: factors influencing auditory-based communication outcomes in children with hearing loss.

OBJECTIVE: The purpose of this study was to determine the influence of selected predictive factors, primarily age at fitting of amplification and degree of hearing loss, on auditory-based outcomes in young children with bilateral sensorineural hearing loss. DESIGN: Forty-four infants and toddlers, first identified with mild to profound bilateral hearing loss, who were being fitted with amplification were enrolled in the study and followed longitudinally. Subjects were otherwise typically developing with no evidence of cognitive, motor, or visual impairment. A variety of subject factors were measured or documented and used as predictor variables, including age at fitting of amplification, degree of hearing loss in the better hearing ear, cochlear implant status, intensity of oral education, parent-child interaction, and the number of languages spoken in the home. These factors were used in a linear multiple regression analysis to assess their contribution to auditory-based communication outcomes. Five outcome measures, evaluated at regular intervals in children starting at age 3, included measures of speech perception (Pediatric Speech Intelligibility and Online Imitative Test of Speech Pattern Contrast Perception), speech production (Arizona-3), and spoken language (Reynell Expressive and Receptive Language). RESULTS: The age at fitting of amplification ranged from 1 to 72 mo, and the degree of hearing loss ranged from mild to profound. Age at fitting of amplification showed the largest influence and was a significant factor in all outcome models. The degree of hearing loss was an important factor in the modeling of speech production and spoken language outcomes. Cochlear implant use was the other factor that contributed significantly to speech perception, speech production, and language outcomes. Other factors contributed sparsely to the models. CONCLUSIONS: Prospective longitudinal studies of children are important to establish relationships between subject factors and outcomes. This study clearly demonstrated the importance of early amplification on communication outcomes. This demonstration required a participant pool that included children who have been fit at very early ages and who represent all degrees of hearing loss. Limitations of longitudinal studies include selection biases. Families who enroll tend to have high levels of education and rate highly on cooperation and compliance measures. Although valuable information can be extracted from prospective studies, not all factors can be evaluated because of enrollment constraints.

Newborn hearing screening speeds diagnosis and access to intervention by 20-25 months.

BACKGROUND: Newborn Hearing Screening (NHS) programs aim to reduce the age of identification and intervention of infants with hearing loss. It is generally accepted that NHS programs achieve that outcome, but few studies have compared children who were screened to those not screened in the same study and during the same time period. This study takes advantage of the emerging screening programs in California to compare children based on screening status on age at intervention milestones. PURPOSE: The purpose of this studywas to compare the outcomes of cohorts of children with hearing loss, some screened for hearing loss at birth and others not screened. Specifically, the measures compared are the benchmarks suggested by the Joint Committee on Infant hearing for determining the quality of screening programs. STUDY SAMPLE: Records from 64 children with bilateral permanent hearing loss who were enrolled in a study of communication outcomes served as data for this study. Of these children, 47 were screened with 39 failing and 8 passing, and 17 were not screened. INTERVENTION: This study was observational and involved no planned intervention. DATA COLLECTION AND ANALYSIS: Outcome benchmarks included age at diagnosis of hearing loss, age at fitting of amplification, and age at enrollment in early intervention. Delays between diagnosis and fitting or enrollment were also calculated. Hearing screening status of the children included screened with fail outcome, screened with pass outcome, and not screened. Analysis included simple descriptive statistics, and t-tests were used to compare outcomes by groups: screened/not screened, screened pass/screened failed, and passed/not screened. RESULTS: Children with hearing loss who had been screened as newborns were diagnosed with hearing loss 24.62 months earlier, fitted with hearing aids 23.51 months earlier, and enrolled in early intervention 19.98 months earlier than those infants who were not screened. Screening status did not influence delays in fitting of amplification or enrollment in intervention following diagnosis. Eight of the infants with hearing loss (12.5%) passed the NHS, and the ages at benchmarks of those children were slightly but not significantly earlier than infants who had not been screened. CONCLUSIONS: The age at achievement of benchmarks such as diagnosis, fitting of amplification, and enrollment in early intervention in children who were screened for hearing loss is on target with stated goals provided by the Academy of Pediatrics and the Joint Committee on Infant Hearing. In addition, children who are not screened for hearing loss continue to show dramatic delays in achievement of benchmarks by as much as 24 months. Evaluating achievement of benchmarks during the start-up period of NHS programs allowed a direct evaluation of ability of these screening programs to meet stated goals. This demonstrates, unequivocally, that the NHS process itself is responsible for improvements in age at diagnosis, hearing aid fitting, and enrollment in intervention.

A prospective, longitudinal study of the impact of GJB2/GJB6 genetic testing on the beliefs and attitudes of parents of deaf and hard-of-hearing infants.

There are limited data on the impact of incorporating genetic counseling and testing into the newborn hearing screening process. We report on results from a prospective, longitudinal study to determine the impact of genetic counseling and GJB2/GJB6 genetic testing on parental knowledge, attitudes, and beliefs about genetic testing. One hundred thirty culturally hearing parents of 93 deaf or hard-of-hearing children ages 0-3 years primarily identified through newborn hearing screening received pre- and post-test genetic counseling for GJB2 and GJB6. Parents completed questionnaires following pre-test counseling, and 1- and 6-month post-test result disclosure. Results indicate that following pre-test counseling all parents perceived benefits to genetic testing. While parents who received positive results continued to perceive benefits from testing, perceived benefit declined among parents who received inconclusive or negative results. Parents did not perceive genetic testing as harmful following pre-test counseling or receipt of test results. Parents who received positive test results performed better in understanding recurrence and causation of their child's deafness and indicated greater interest in prenatal genetic testing than those who received inconclusive or negative test results. Parents felt that pediatricians and audiologists should inform parents of genetic testing availability; however, there was no consensus on timing of this discussion. Thus culturally hearing parents do not perceive genetic testing of their deaf or hard-of-hearing infants/toddlers as harmful; they feel that primary care providers should discuss genetic testing with them; and positive genetic test results with genetic counseling give rise to better understanding and perceived benefit than negative or inconclusive results.

Comment on "Ear Asymmetries in middle-ear, cochlear, and brainstem responses in human infants" [J. Acoust. Soc. Am. 123, 1504-1512].

Following Sininger and Cone-Wesson [Science 305, 1581], Sininger and Cone-Wesson [Hear. Res. 212, 203-211], Keefe et al. [J. Acoust. Soc. Am. 123(3), 1504-1512] described ear asymmetries in middle ear, cochlear, and brainstem responses of infants. Keefe et al. state that their data do not support the findings of Sininger and Cone-Wesson [Science 305, 1581] who found asymmetries in evoked otoacoustic emissions and auditory brainstem responses and proposed that stimulus-directed asymmetries in processing may facilitate development of hemispheric specialization. The Keefe et al. findings, in fact, replicated and extended the findings of Sininger and Cone-Wesson (2004, 2006) and support, rather than refute, the conclusions. Keefe et al. controlled neither the background noise nor averaging time across test conditions (ear or otoacoustic emission type) and thus their separate analyses of signal and noise magnitude exceed the limitations imposed by the data collection methods.

Asymmetry of temporal processing in listeners with normal hearing and unilaterally deaf subjects.

OBJECTIVES: In general, auditory cortex on the left side of the brain is specialized for processing of acoustic stimuli with complex temporal structure including speech, and the right hemisphere is primary for spectral processing and favors tonal stimuli and music. This asymmetry in processing is further emphasized when hemisphere-favored stimuli are presented to the contralateral ear. The purpose of the first experiment is to further investigate the properties that dictate lateralized processing of auditory stimuli by ear and the relationship between auditory task and stimulus type. Next, it is not clear what compensation may exist for the loss of function of one ear and consequently, reduced access to functions primary performed in the opposite hemisphere, in the case of early unilateral profound hearing loss. The purpose of experiment 2 is to determine if any compensation for loss of function is seen in persons with early unilateral deafness. DESIGN: Experiment 1: Gap detection thresholds were determined in 30 right-handed listeners with normal hearing using wide-band noise markers (temporally complex), 400 and 4000 Hz pure tones presented individually to the left and right ears. Experiment 2: The same procedure was administered to listeners with early-onset, severe-to-profound unilateral deafness (seven left ear deaf and five right ear deaf) in the hearing ear alone. RESULTS: A significant right ear advantage was found for gap detection threshold using noise markers and a smaller left ear advantage was found for tonal stimuli. Listeners with unilateral deafness demonstrated that the hearing ear, left or right, performed in a manner similar to listeners with normal hearing. CONCLUSIONS: Results indicate that (1) gap marker, more than task, was the salient feature in determining laterality of processing in this experiment, (2) the two ears have distinct processing capacity based on stimulus type, and (3) compensation for loss is not apparent in persons with congenital unilateral deafness.

Infant hearing loss and connexin testing in a diverse population.

PURPOSE: Previous studies of connexin-related hearing loss have typically reported on mixed age groups or adults. To further address epidemiology and natural history of connexin-related hearing loss, we conducted a longitudinal study in an ethnically diverse cohort of infants and toddlers under 3 years of age. Our study compares infants with and without connexin-related hearing loss to examine differences in the prevalence of connexin and non-connexin-related hearing loss by ethnic origin, detection by newborn hearing screening, phenotype, neonatal risk factors, and family history. This is the first study to differentiate infants with and without connexin-related hearing loss. METHODS: We enrolled 95 infants with hearing loss from whom both exons of Cx26 were sequenced and the Cx30 deletion was assayed. Demographic, family history, newborn hearing screening data, perinatal, and audiologic records were analyzed. RESULTS: Genetic testing identified biallelic Cx26/30 hearing loss-associated variants in 24.7% of infants with a significantly lower prevalence in Hispanic infants (9.1%). Eighty-two infants underwent newborn hearing screening; 12 infants passed, 3 had connexin-related hearing loss. No differences in newborn hearing screening pass rate, neonatal complications, or hearing loss severity were detected between infants with and without connexin-related hearing loss. Family history correlates with connexin-related hearing loss. CONCLUSIONS: Connexin-related hearing loss occurs in one quarter of infants in an ethnically diverse hearing loss population but with a lower prevalence in Hispanic infants. Not all infants with connexin-related hearing loss fail newborn hearing screening. Family history correlates significantly with connexin-related hearing loss. Genetic testing should not be deferred because of newborn complications. These results will have an impact on genetic testing for infant hearing loss.

Ethnic differences in parental perceptions of genetic testing for deaf infants.

As genetic testing becomes an integral part of the evaluation of deaf infants and children, it is important to understand parental views on genetic testing. The purpose of this study is to examine parental reasons for, and beliefs about, genetic testing for deafness in early-identified infants, and to determine if they differ as a function of ethnicity. We present baseline data collected from 56 Caucasian, 59 Hispanic, and 24 Asian parents of deaf children participating in a longitudinal, prospective study on genetic testing for connexin-related deafness. The overall finding is that reasons for, and beliefs about, genetic testing for deafness varied as a function of ethnicity. Virtually all parents sought genetic testing to understand why their child is deaf. However, Asian and/or Hispanic parents were more likely than Caucasian parents to view family planning, helping with their child's medical care, and helping the family as other important reasons for testing, and were more likely than Caucasian parents to perceive genetic testing to be useful for these purposes. Asian and Hispanic parents were more likely than Caucasian parents to perceive genetic testing in harmful terms. Genetic testing fulfills a cognitive need for parents to understand why their child is deaf, yet differences in responses suggest that Asian and Hispanic parents may seek testing for other purposes. Understanding different perspectives on genetic testing for deafness will enhance genetic counselors' cultural competence and facilitate the pre-test genetic counseling session.

Stimulus repetition rate and the reference levels for clicks and short tone bursts: a warning to audiologists, researchers, calibration laboratories, and equipment manufacturers.

PURPOSE: To make the audiologic community aware of a technical issue with potential for misunderstanding that could affect the design, calibration, and use of auditory brainstem response (ABR) systems. METHOD: Two international standards published in 2007 relating to the stimuli commonly used in ABR tests were studied and the behavior of a commercially available ABR system examined with regard to the relationship between stimulus level and repetition rate. RESULTS: There is potential for misunderstanding of the need to compensate for the effect of stimulus rate on stimulus level. Although rapidly presented stimuli appear louder as the rate is increased, it is inappropriate to compensate for this when calibrating the stimulus level of ABR systems. CONCLUSIONS: Users of ABR systems should, if possible, use the stimulus reference levels now available in an international standard rather than establish local values. No adjustment of level should be made to account for different stimulus repetition rates. Users of ABR systems should check their systems to ensure that no automatic level adjustment is made; if necessary, equipment manufacturers should be consulted.

Dichotic listening after cerebral hemispherectomy: methodological and theoretical observations.

We examined two commonly used dichotic listening tests for measuring the degree of hemispheric specialization for language in individuals who had undergone cerebral hemispherectomy: the consonant-vowel (CV) nonsense syllables and the fused words (FW) tests, using the common laterality indices f and lambda. Hemispherectomy on either side resulted in a massive contralateral ear advantage, demonstrating nearly complete ipsilateral suppression of the left ear in the right hemispherectomy group but slightly less complete suppression of the right ear in the left hemispherectomy group. The results are consistent with the anatomical model of the ear advantage [Kimura, D. (1961). Most syllables or words are reported for the ear contralateral to the remaining hemisphere, while few or none are reported for the ear ipsilateral to the remaining hemisphere. In the presence of competing inputs to the two ears, the stronger contralateral ear-hemisphere connection dominates/suppresses the weaker ipsilateral ear-hemisphere connection. The lambda index was similar in the two tests but the index f was higher in the CV than the FW test. Both indices of the CV test were sensitive to side of resection, higher in the right hemispherectomy than in the left hemispherectomy groups.

Lateral asymmetry in the ABR of neonates: evidence and mechanisms.

Lateralized processing of auditory stimuli occurs at the level of the auditory cortex but differences in function between the left and right sides are not clear at lower levels of the auditory system. The current study is designed to (1) investigate asymmetric auditory function at the ear and brainstem in human infants and (2) investigate possible mechanisms for asymmetry at these levels. Study 1 evaluated auditory brainstem responses (ABRs) in response to high and low-level clicks presented to the right and left ears of neonates. Wave V was significantly larger in amplitude and waves III and V were shorter in latency when the ABR was generated in the right ear. Study 2 investigated two possible mechanisms of such asymmetry by (a) using contralateral white noise masking to activate the medial olivocochlear system and (b) increasing stimulus rate to reveal neural conduction and synaptic mechanisms. ABR wave V, evoked by clicks to the left ear, showed a greater reduction in amplitude with contralateral noise than the response evoked from the right ear. No systematic asymmetries in ABR latencies or amplitudes were found with increased stimulus rate. We conclude that (1) the click-evoked ABR in neonates demonstrates asymmetric auditory function with a small but significant right ear advantage and (2) asymmetric activation of the medial olivocochlear system, specifically greater contralateral suppression of ABR produced by the left ear, is a possible mechanism for asymmetry.