Barbara Cone

Slight-mild sensorineural hearing loss in children: audiometric, clinical, and risk factor profiles.

Objectives: Slight or mild hearing loss has been posited as a factor affecting speech, language, learning, and academic outcomes, but the risk factors for slight-mild sensorineural hearing loss (SNHL) have not been ascertained. The two specific aims for this research were (1) to describe the audiometric and clinical characteristics of children identified with slight-mild bilateral SNHL and (2) to compare children with slight-mild SNHL with those with normal hearing (NH) with respect to potential risk factors for congenital or acquired for hearing loss. Design: A cross-sectional cluster sample survey of 6581 children enrolled in years 1 and 5 of Australian elementary school was completed. Children were screened for slight-mild SNHL, defined as a low- and/or high-frequency pure-tone average of 16 to 40 dB HL in the better ear, with air-bone gaps <10 dB. Children who did not pass the screen received air and bone conduction threshold and tympanometry tests to determine the type and degree of hearing loss. The parents of every child who participated in this study completed a questionnaire, before the hearing screening, to ascertain possible risk indicators. The questionnaire included items regarding the familys demographics, hearing status of family members, the presence of risk factors, and parental concern regarding the childs hearing. Results: Fifty-five children with slight-mild SNHL and 5490 with NH were identified. Of the group with SNHL, 39 children had a slight loss (16 to 25 dB HL) and 16 had a mild loss (26 to 40 dB HL). The majority of the losses were bilateral and symmetrical, and the mean pure-tone average for the better ear for all 55 children was 22.4 dB HL (SD, 5.2). The most prevalent risk factor was “neonatal intensive care unit/special care nursery admission,” which was reported for 12.5% of the SNHL and 8.4% of the NH group. Reported use of personal stereos was a significant risk factor with an odds ratio of 1.7 (95% confidence interval = 1.0 to 3.0, p = 0.05). The questions relating to parental concern for their childs hearing had low sensitivity (<30%) and very low positive predictive values (<3%) for detecting slight-mild SNHL. Conclusions: Slight-mild SNHL had a prevalence of 0.88% among the school-aged population sampled, with the majority of these children exhibiting bilateral, symmetrical audiometric configurations. Conventional risk factors for hearing loss were not strongly predictive of slight-mild SNHL nor were parental concerns about the childs hearing ability. The association between slight-mild SNHL and the parent report of personal stereo use suggests that this type of noise exposure may be a risk factor for acquired hearing loss. This seems to be the first documentation of such an association in a large sample of young children.

Dynamics of infant cortical auditory evoked potentials (CAEPs) for tone and speech tokens

OBJECTIVES Cortical auditory evoked potentials (CAEPs) to tones and speech sounds were obtained in infants to: (1) further knowledge of auditory development above the level of the brainstem during the first year of life; (2) establish CAEP input-output functions for tonal and speech stimuli as a function of stimulus level and (3) elaborate the data-base that establishes CAEP in infants tested while awake using clinically relevant stimuli, thus providing methodology that would have translation to pediatric audiological assessment. Hypotheses concerning CAEP development were that the latency and amplitude input-output functions would reflect immaturity in encoding stimulus level. In a second experiment, infants were tested with the same stimuli used to evoke the CAEPs. Thresholds for these stimuli were determined using observer-based psychophysical techniques. The hypothesis was that the behavioral thresholds would be correlated with CAEP input-output functions because of shared cortical response areas known to be active in sound detection. DESIGN 36 infants, between the ages of 4 and 12 months (mean=8 months, s.d.=1.8 months) and 9 young adults (mean age 21 years) with normal hearing were tested. First, CAEPs amplitude and latency input-output functions were obtained for 4 tone bursts and 7 speech tokens. The tone bursts stimuli were 50 ms tokens of pure tones at 0.5, 1.0, 2.0 and 4.0 kHz. The speech sound tokens, /a/, /i/, /o/, /u/, /m/, /s/, and /∫/, were created from natural speech samples and were also 50 ms in duration. CAEPs were obtained for tone burst and speech token stimuli at 10 dB level decrements in descending order from 70 dB SPL. All CAEP tests were completed while the infants were awake and engaged in quiet play. For the second experiment, observer-based psychophysical methods were used to establish perceptual threshold for the same speech sound and tone tokens. RESULTS Infant CAEP component latencies were prolonged by 100-150 ms in comparison to adults. CAEP latency-intensity input output functions were steeper in infants compared to adults. CAEP amplitude growth functions with respect to stimulus SPL are adult-like at this age, particularly for the earliest component, P1-N1. Infant perceptual thresholds were elevated with respect to those found in adults. Furthermore, perceptual thresholds were higher, on average, than levels at which CAEPs could be obtained. When CAEP amplitudes were plotted with respect to perceptual threshold (dB SL), the infant CAEP amplitude growth slopes were steeper than in adults. CONCLUSIONS Although CAEP latencies indicate immaturity in neural transmission at the level of the cortex, amplitude growth with respect to stimulus SPL is adult-like at this age, particularly for the earliest component, P1-N1. The latency and amplitude input-output functions may provide additional information as to how infants perceive stimulus level. The reasons for the discrepancy between electrophysiologic and perceptual threshold may be due to immaturity in perceptual temporal resolution abilities and the broad-band listening strategy employed by infants. The findings from the current study can be translated to the clinical setting. It is possible to use tonal or speech sound tokens to evoke CAEPs in an awake, passively alert infant, and thus determine whether these sounds activate the auditory cortex. This could be beneficial in the verification of hearing aid or cochlear implant benefit.

The medial olivocochlear reflex in children during active listening

Abstract Objective: To determine if active listening modulates the strength of the medial olivocochlear (MOC) reflex in children. Design: Click-evoked otoacoustic emissions (CEOAEs) were recorded from the right ear in quiet and in four test conditions: one with contralateral broadband noise (BBN) only, and three with active listening tasks wherein attention was directed to speech embedded in contralateral BBN. Study sample: Fifteen typically-developing children (ranging in age from 8 to14 years) with normal hearing. Results: CEOAE levels were reduced in every condition with contralateral acoustic stimulus (CAS) when compared to preceding quiet conditions. There was an additional systematic decrease in CEOAE level with increased listening task difficulty, although this effect was very small. These CEOAE level differences were most apparent in the 8–18 ms region after click onset. Conclusions: Active listening may change the strength of the MOC reflex in children, although the effects reported here are very subtle. Further studies are needed to verify that task difficulty modulates the activity of the MOC reflex in children.

Dichotic listening and otoacoustic emissions: shared variance between cochlear function and dichotic listening performance in adults with normal hearing.

The present study investigated a possible connection between speech processing and cochlear function. Twenty-two subjects with age range from 18 to 39, balanced for gender with normal hearing and without any known neurological condition, were tested with the dichotic listening (DL) test, in which listeners were asked to identify CV-syllables in a nonforced, and also attention-right, and attention-left condition. Transient evoked otoacoustic emissions (TEOAEs) were recorded for both ears, with and without the presentation of contralateral broadband noise. The main finding was a strong negative correlation between language laterality as measured with the dichotic listening task and of the TEOAE responses. The findings support a hypothesis of shared variance between central and peripheral auditory lateralities, and contribute to the attentional theory of auditory lateralization. The results have implications for the understanding of the cortico-fugal efferent control of cochlear activity.

Contralateral inhibition of click- and chirp-evoked human compound action potentials

Cochlear outer hair cells (OHC) receive direct efferent feedback from the caudal auditory brainstem via the medial olivocochlear (MOC) bundle. This circuit provides the neural substrate for the MOC reflex, which inhibits cochlear amplifier gain and is believed to play a role in listening in noise and protection from acoustic overexposure. The human MOC reflex has been studied extensively using otoacoustic emissions (OAE) paradigms; however, these measurements are insensitive to subsequent “downstream” efferent effects on the neural ensembles that mediate hearing. In this experiment, click- and chirp-evoked auditory nerve compound action potential (CAP) amplitudes were measured electrocochleographically from the human eardrum without and with MOC reflex activation elicited by contralateral broadband noise. We hypothesized that the chirp would be a more optimal stimulus for measuring neural MOC effects because it synchronizes excitation along the entire length of the basilar membrane and thus evokes a more robust CAP than a click at low to moderate stimulus levels. Chirps produced larger CAPs than clicks at all stimulus intensities (50–80 dB ppeSPL). MOC reflex inhibition of CAPs was larger for chirps than clicks at low stimulus levels when quantified both in terms of amplitude reduction and effective attenuation. Effective attenuation was larger for chirp- and click-evoked CAPs than for click-evoked OAEs measured from the same subjects. Our results suggest that the chirp is an optimal stimulus for evoking CAPs at low stimulus intensities and for assessing MOC reflex effects on the auditory nerve. Further, our work supports previous findings that MOC reflex effects at the level of the auditory nerve are underestimated by measures of OAE inhibition.

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.

Infant cortical electrophysiology and perception of vowel contrasts

Cortical auditory evoked potentials (CAEPs) were obtained for vowel tokens presented in an oddball stimulus paradigm. Perceptual measures of vowel discrimination were obtained using a visually-reinforced head-turn paradigm. The hypothesis was that CAEP latencies and amplitudes would differ as a function of vowel type and be correlated with perceptual performance. Twenty normally hearing infants aged 4-12 months were evaluated. CAEP component amplitudes and latencies were measured in response to the standard, frequent token /a/ and for infrequent, deviant tokens /i/, /o/ and /u/, presented at rates of 1 and 2 tokens/s. The perceptual task required infants to make a behavioral response for trials that contained two different vowel tokens, and ignore those in which the tokens were the same. CAEP amplitudes were larger in response to the deviant tokens, when compared to the control condition in which /a/ served as both standard and deviant. This was also seen in waveforms derived by subtracting the response to standard /a/ from the responses to deviant tokens. CAEP component latencies in derived responses at 2/s also demonstrated some sensitivity to vowel contrast type. The average hit rate for the perceptual task was 68.5%, with a 25.7% false alarm rate. There were modest correlations of CAEP amplitudes and latencies with perceptual performance. The CAEP amplitude differences for vowel contrasts could be used as an indicator of the underlying neural capacity to encode spectro-temporal differences in vowel sounds. This technique holds promise for translation to clinical methods for evaluating speech perception.

Behavioral Pure-Tone Threshold Shifts Caused by Tympanic Membrane Electrodes.

Objective: To determine whether tympanic membrane (TM) electrodes induce behavioral pure-tone threshold shifts. Design: Pure-tone thresholds (250 to 8000 Hz) were measured twice in test (n = 18) and control (n = 10) groups. TM electrodes were placed between first and second threshold measurements in the test group, whereas the control group did not receive electrodes. Pure-tone threshold shifts were compared between groups. The effect of TM electrode contact location on threshold shifts was evaluated in the test group. Results: TM electrodes significantly increased average low-frequency thresholds, 7.5 dB at 250 Hz and 4.2 dB at 500 Hz, and shifts were as large as 25 dB in individual ears. Also, threshold shifts did not appear to vary at any frequency with TM electrode contact location. Conclusions: Low-frequency threshold shifts occur when using TM electrodes and insert earphones. These findings are relevant to interpreting electrocochleographic responses to low-frequency stimuli.

Efferent modulation of pre-neural and neural distortion products

ABSTRACT Distortion product otoacoustic emissions (DPOAEs) and distortion product frequency following responses (DPFFRs) are respectively pre‐neural and neural measurements associated with cochlear nonlinearity. Because cochlear nonlinearity is putatively linked to outer hair cell electromotility, DPOAEs and DPFFRs may provide complementary measurements of the human medial olivocochlear (MOC) reflex, which directly modulates outer hair cell function. In this study, we first quantified MOC reflex‐induced DPOAE inhibition at spectral fine structure peaks in 22 young human adults with normal hearing. The f1 and f2 tone pairs producing the largest DPOAE fine structure peak for each subject were then used to evoke DPFFRs with and without MOC reflex activation to provide a related neural measure of efferent inhibition. We observed significant positive relationships between DPOAE fine structure peak inhibition and inhibition of DPFFR components representing neural phase locking to f2 and 2f1‐f2, but not f1. These findings may support previous observations that the MOC reflex inhibits DPOAE sources differentially. That these effects are maintained and represented in the auditory brainstem suggests that the MOC reflex may exert a potent influence on subsequent subcortical neural representation of sound. HIGHLIGHTSWe examined relationships between pre‐neural DPOAE and neural DPFFR inhibition with contralateral noise.Both responses were inhibited with contralateral noise.DPOAE inhibition was related to inhibition of DPFFR components corresponding to f2 and 2f1‐f2 frequencies.Results provide evidence of neural consequences of efferent inhibition, which has mainly been tested with pre‐neural assays.

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.