Acoustic Change Complex and Visually Reinforced Infant Speech Discrimination Measures of Vowel Contrast Detection.

OBJECTIVES: To measure the effect of stimulus rate and vowel change direction on the acoustic change complex (ACC) latencies and amplitudes and compare ACC metrics to behavioral measures of vowel contrast detection for infants tested under the age of 1 year. We tested the hypothesis that the direction of spectral energy shift from a vowel change would result in differences in the ACC, owing to the sensitivity of cortical neurons to the direction of frequency change. We evaluated the effect of the stimulus rate (1/s versus 2/s) on the infants' ACC. We evaluated the ACC amplitude ratio's sensitivity (proportion of ACCs present for each change trial) and compared it to perceptual responses obtained using a visually reinforced infant speech discrimination paradigm (VRISD). This report provides normative data from infants for the ACC toward the ultimate goal of developing a clinically useful index of neural capacity for vowel discrimination. DESIGN: Twenty-nine infants, nine females, 4.0 to 11.8 months of age, participated. All participants were born at full term and passed their newborn hearing screens. None had risk factors for hearing or neurologic impairment. Cortical auditory evoked potentials were obtained in response to synthesized vowel tokens /a/, /i/, /o/, and /u/ presented at a rate of 1- or 2/s in an oddball stimulus paradigm with a 25% probability of the deviant stimulus. All combinations of vowel tokens were tested at the two rates. The ACC was obtained in response to the deviant stimulus. The infants were also tested for vowel contrast detection using a VRISD paradigm with the same combinations of vowel tokens used for the ACC. The mean age at the time of the ACC test was 5.4 months, while the mean age at the behavioral test was 6.8 months. RESULTS: Variations in ACC amplitude and latency occurred as a function of the initial vowel token and the contrast token. However, the hypothesis that the direction of vowel (spectral) change would result in significantly larger change responses for high-to-low spectral changes was not supported. The contrasts with /a/ as the leading vowel of the contrast pair resulted in the largest ACC amplitudes than other conditions. Significant differences in the ACC presence and amplitude were observed as a function of rate, with 2/s resulting in ACCs with the largest amplitude ratios. Latency effects of vowel contrast and rate were present, but not systematic. The ACC amplitude ratio's sensitivity for detecting a vowel contrast was greater for the 2/s rate than the 1/s rate. For an amplitude ratio criterion of ≥1.5, the sensitivity was 93% for ACC component P2-N2 at 2/s, whereas at 1/s sensitivity was 70%. VRISD tests of vowel-contrast detection had a 71% hit and a 21% false-positive rate. Many infants who could not reach performance criteria for VRISD had ACC amplitude ratios of ≥2.0. CONCLUSIONS: The ACC for vowel contrasts presented at a rate of 2/s is a robust index of vowel-contrast detection when obtained in typically developing infants under the age of 1 year. The ACC is present in over 90% of infants tested at this rate when an amplitude ratio criterion of ≥1.5 is used to define a response. The amplitude ratio appears to be a sensitive metric for the difference between a control and contrast condition. The ACC can be obtained in infants who do not yet exhibit valid behavioral responses for vowel change contrasts and may be useful for estimating neural capacity for discriminating these sounds.

Perceptual and Electrophysiological Correlates of Fixed Versus Moving Sound Source Lateralization.

Purpose The aims of the study were (a) to evaluate the effects of systematically varied factors of stimulus duration, interaural-level difference (ILD), and direction on perceptual and electrophysiological metrics of lateralization for fixed versus moving targets and (b) to evaluate the hemispheric activity underlying perception of fixed versus moving auditory targets. Method Twelve normal-hearing, young adult listeners were evaluated using perceptual and P300 tests of lateralization. Both perceptual and P300 tests utilized stimuli that varied for type (fixed and moving), direction (right and left), duration (100 and 500 ms), and magnitude of ILD (9 and 18 dB). Listeners provided laterality judgments and stimulus-type discrimination (fixed vs. moving) judgments for all combinations of acoustic factors. During P300 recordings, listeners discriminated between left- versus right-directed targets, as the other acoustic parameters were varied. Results ILD magnitude and stimulus type had statistically significant effects on laterality ratings, with larger magnitude ILDs and fixed type resulting in greater lateralization. Discriminability between fixed versus moving targets was dependent on stimulus duration and ILD magnitude. ILD magnitude was a significant predictor of P300 amplitude. There was a statistically significant inverse relationship between the perceived velocity of targets and P300 latency. Lateralized targets evoked contralateral hemispheric P300 activity. Moreover, a right-hemisphere enhancement was observed for fixed-type lateralized deviant stimuli. Conclusions Perceptual and P300 findings indicate that lateralization of auditory movement is highly dependent on temporal integration. Both the behavioral and physiological findings of this study suggest that moving auditory targets with ecologically valid velocities are processed by the central auditory nervous system within a window of temporal integration that is greater than that for fixed auditory targets. Furthermore, these findings lend support for a left hemispatial perceptual bias and right hemispheric dominance for spatial listening.

Sensitivity and Specificity of Pure-Tone and Subjective Hearing Screenings Using Spanish-Language Questions.

Purpose The purpose of this study is to determine the sensitivities and specificities of different audiometric hearing screening criteria and single-item and multi-item hearing disability questionnaires among a group of Spanish-speaking adults in a rural community. Method Participants were 131 predominantly older (77% 65+ years) Hispanic/Latinx adults (98%). A structured Spanish-language interview and pure-tone threshold test data were analyzed for each participant. The sensitivities and specificities of three single questions and the Hearing Handicap Index for the Elderly-Screening (HHIE-S; Ventry & Weinstein, 1983) in Spanish, as well as three audiometric screening criteria, were evaluated in relation to the pure-tone threshold test for detecting hearing loss. Results Sensitivity and specificity of audiometric screening criteria varied, but the highest sensitivity was found for the criterion of > 25 dB HL at 1-4 kHz in either ear. The single self-perception question, "¿Cree usted que tiene pérdida de audición? (Do you think you have a hearing loss?)," was shown to be the most sensitive self-report screening compared to other single-item questions and the HHIE-S. This single question was as sensitive as an audiometric screening to detect a moderate hearing loss (> 40 dB HL in either ear). Results from the Spanish HHIE-S indicated poor performance to detect hearing loss in this population, consistent with previous research. Conclusions Among older Spanish-speaking adults, self-reported hearing status had varying sensitivities depending on the question asked. However, of the tools evaluated, the self-perception question proved to be a more sensitive and specific tool than a multi-item screen. Objective audiometric testing (> 25 dB HL) resulted in the highest sensitivity to detect a mild hearing loss.

Evidence of Vowel Discrimination Provided by the Acoustic Change Complex.

OBJECTIVES: The objectives of this study were to measure the effects of level and vowel contrast on the latencies and amplitudes of acoustic change complex (ACC) in the mature auditory system. This was done to establish how the ACC in healthy young adults is affected by these stimulus parameters that could then be used to inform translation of the ACC into a clinical measure for the pediatric population. Another aim was to demonstrate that a normalized amplitude metric, calculated by dividing the ACC amplitude in the vowel contrast condition by the ACC amplitude obtained in a control condition (no vowel change) would demonstrate good sensitivity with respect to perceptual measures of vowel-contrast detection. The premises underlying this research were that: (1) ACC latencies and amplitudes would vary with level, in keeping with principles of an increase in neural synchrony and activity that takes place as a function of increasing stimulus level; (2) ACC latencies and amplitudes would vary with vowel contrast, because cortical auditory evoked potentials are known to be sensitive to the spectro-temporal characteristics of speech. DESIGN: Nineteen adults, 14 of them female, with a mean age of 24.2 years (range 20 to 38 years) participated in this study. All had normal-hearing thresholds. Cortical auditory evoked potentials were obtained from all participants in response to synthesized vowel tokens (/a/, /i/, /o/, /u/), presented in a quasi-steady state fashion at a rate of 2/sec in an oddball stimulus paradigm, with a 25% probability of the deviant stimulus. The ACC was obtained in response to the deviant stimulus. All combinations of vowel tokens were tested at 2 stimulus levels: 40 and 70 dBA. In addition, listeners were tested for their ability to detect the vowel contrasts using behavioral methods. RESULTS: ACC amplitude varied systematically with level, and test condition (control versus contrast) and vowel token, but ACC latency did not. ACC amplitudes were significantly larger when tested at 70 dBA compared with 40 dBA and for contrast trials compared with control trials at both levels. Amplitude ratios (normalized amplitudes) were largest for contrast pairs in which /a/ was the standard token. The amplitude ratio metric at the individual level demonstrated up to 97% sensitivity with respect to perceptual measures of discrimination. CONCLUSIONS: The present study establishes the effects of stimulus level and vowel type on the latency and amplitude of the ACC in the young adult auditory system and supports the amplitude ratio as a sensitive metric for cortical acoustic salience of vowel spectral features. Next steps are to evaluate these methods in infants and children with hearing loss with the long-term goal of its translation into a clinical method for estimating speech feature discrimination.

Central deafness: a review of past and current perspectives.

Objective: The purpose of this review was to describe and differentiate clinical syndromes caused by lesions of the central auditory nervous system (CANS). Design: Relevant literature was identified through Pubmed and Google Scholar searches using the key terms: central deafness, auditory agnosia, word deafness and cortical deafness. Given the authors' intent to review past and current perspectives on central deafness, no publication date range was imposed. Study sample: The review is organised around complete central deafness (CCD), central deafness (CD), word deafness and nonverbal agnosia (NVA), including anatomy and pathophysiology, symptom profile and audiological findings. Four case studies are presented to demonstrate the clinical correlates of CD. Conclusions: Central deafness is a rare condition typically resulting from bilateral compromise of the CANS. The closer to the auditory cortex bilateral lesions are located, the greater the probability of CD. A variety of symptoms present with or appear subsequent to CD, including tinnitus, hallucinations, voice changes and hypersensitivity to sounds (if heard by the patient), as well as diverse neurological symptoms depending on the non-auditory areas of the brain that may also be involved. Thorough and appropriate audiological testing is critical to accurately diagnose CD and its variants.

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.

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.

The medial olivocochlear reflex in children during active listening.

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.

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.

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 MOC reflex during active listening to speech.

PURPOSE: The purpose of this study was to test the hypothesis that active listening to speech would increase medial olivocochlear (MOC) efferent activity for the right vs. the left ear. METHOD: Click-evoked otoacoustic emissions (CEOAEs) were evoked by 60-dB p.e. SPL clicks in 13 normally hearing adults in 4 test conditions for each ear: (a) in quiet; (b) with 60-dB SPL contralateral broadband noise; (c) with words embedded (at -3-dB signal-to-noise ratio [SNR]) in 60-dB SPL contralateral noise during which listeners directed attention to the words; and (d) for the same SNR as in the 3rd condition, with words played backwards. RESULTS: There was greater suppression during active listening compared with passive listening that was apparent in the latency range of 6- to 18-ms poststimulus onset. Ear differences in CEOAE amplitude were observed in all conditions, with right-ear amplitudes larger than those for the left. The absolute difference between CEOAE amplitude in quiet and with contralateral noise, a metric of suppression, was equivalent for right and left ears. When the amplitude differences were normalized, suppression was greater for noise presented to the right and the effect measured for a probe in the left ear. CONCLUSION: The findings support the theory that cortical mechanisms involved in listening to speech affect cochlear function through the MOC efferent system.

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.

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 family's demographics, hearing status of family members, the presence of risk factors, and parental concern regarding the child's 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 child's 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 child's 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.

Auditory steady-state responses and speech feature discrimination in infants.

PURPOSE: The aim of this study was to determine whether there was a correlation between auditory steady-state responses (ASSRs) for complex toneburst stimuli and speech feature discrimination (SFD) abilities in young infants. STUDY SAMPLE: Seventeen infants (mean age = 9.4 months) and 21 adults (mean age = 27 years) with normal hearing had ASSR and SFD tests. DATA COLLECTION: The ASSR test employed an eight-component complex toneburst stimulus; threshold and input-output functions were determined as level was systematically varied. The SFD test utilized an observer-based, visual-reinforcement test procedure to determine the infant's ability to detect the speech feature change from /ba/ to /da/. RESULTS: The correlation of the group mean /ba/-/da/ discrimination performance (percent correct) with the group mean ASSR score (percent responses present) ranged from r = 0.64 for the 1500 Hz amplitude-modulated and frequency-modulated tone burst to 0.99 for ASSRs for all stimulus components; however, correlations between ASSRs and SFD scores for individual subjects were modest. CONCLUSION: The ASSR and SFD results appear to reflect the audibility of the stimuli.

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.