Thresholds determined using the monotic and dichotic multiple auditory steady-state response technique in normal-hearing subjects.

Auditory steady-state responses (ASSRs) were elicited by presenting single or multiple, 77-105 Hz amplitude-modulated 0.5, 1, 2, and 4 kHz tones to one or both ears. Objectives of this study were to (i) replicate and extend previous multiple ASSR studies in a quiet double-walled sound booth, and (ii) discover differences (if any) between thresholds assessed in monotic and dichotic conditions, which ranged between 15 and 22dB SPL. The present study's behavioural and ASSR thresholds are 0-10 dB lower (better) than results of previous monotic studies. Further, there are no significant differences in ASSR thresholds between dichotic and monotic stimulus conditions. Therefore, dichotic multiple AM tone stimulation does not produce a change in the ASSR that affects threshold estimation in a clinically significant manner. Thus, at least for detecting normal hearing, the dichotic multiple ASSR technique is a feasible method for estimating hearing thresholds that would substantially reduce recording time compared to conventional single-stimulus techniques.

The effects of decreased audibility produced by high-pass noise masking on N1 and the mismatch negativity to speech sounds /ba/and/da.

This study investigated the effects of decreased audibility produced by high-pass noise masking on the cortical event-related potentials (ERPs) N1 and mismatch negativity (MMN) to the speech sounds /ba/ and /da/, presented at 65 dB SPL. ERPs were recorded while normal listeners (N = 11) ignored the stimuli and read a book. Broadband masking noise was simultaneously presented at an intensity sufficient to mask the response to the speech sounds, and subsequently high-pass filtered. The conditions were QUIET (no noise); high-pass cutoff frequencies of 4000, 2000, 1000, 500, and 250 Hz; and broadband noise. Behavioral measures of discrimination of the speech sounds (d' and reaction time) were obtained separately from the ERPs for each listener and condition. As the cutoff frequency of the high-pass masker was lowered, ERP latencies increased and amplitudes decreased. The cutoff frequency where changes first occurred differed for N1 and MMN. N1 showed small systematic changes across frequency beginning with the 4000-Hz high-pass noise. MMN and behavioral measures showed large changes that occurred at approximately 1000 Hz. These results indicate that decreased audibility, resulting from the masking, affects N1 and the MMN in a differential manner. N1 reflects the presence of audible stimulus energy, being present in all conditions where stimuli were audible, whether or not they were discriminable. The MMN is present only for those conditions where stimuli were behaviorally discriminable. These studies of cortical ERPs in high-pass noise studies provide insight into the changes in brain processes and behavioral performance that occur when audibility is reduced, as in hearing loss.

The effects of broadband noise masking on cortical event-related potentials to speech sounds /ba/ and /da/.

OBJECTIVE: To systematically investigate in normal-hearing listeners the effects of decreased audibility produced by broadband noise masking on the cortical event-related potentials (ERPs) N1, N2, and P3 to the speech sounds /ba/ and /da/. DESIGN: Ten normal-hearing adult listeners actively (button-press response) discriminated the speech sounds /ba/ and /da/ presented in quiet (no masking) or with broadband masking noise (BBN), using an ERP oddball paradigm. The BBN was presented at 50, 60, and 70 dB SPL when speech sounds were presented at 65 dB ppe SPL and at 60, 70 and, 80 dB SPL when speech sounds were presented at 80 dB ppe SPL. RESULTS: On average, the 50, 60, 70, and 80 dB SPL BBN maskers produced behavioral threshold elevations of 18, 25, 35, and 48 dB (average for 250 to 4000 Hz), respectively. The BBN maskers produced significant decreases (relative to quiet condition) in ERP amplitudes and behavioral discriminability. These decreases did not occur, however, until the noise masker intensity (in dB SPL) was equal to or greater than the speech stimulus intensity (in dB ppe SPL), that is, until speech to noise ratios (SNRs) were < or = 0 dB. N1 remained present even after N2, P3, and behavioral discriminability were absent. In contrast to amplitudes, ERP and behavioral latencies showed significant decreases at higher (better) SNRs. Significant latency increases occurred when the noise maskers were within 10 to 20 dB of the stimuli (i.e., SNR < or = 20 dB). The effects of masking were greater for responses to /da/ compared with /ba/. Latency increases occurred with less masking for N1 than for P3 or behavioral reaction time, with N2 falling in between. CONCLUSIONS: These results indicate that decreased audibility as a result of masking affects the various ERP peaks in a differential manner and that latencies are more sensitive indicators of these masking effects than are amplitudes.

Estimation of the pure-tone audiogram by the auditory brainstem response: a review.

This review paper briefly considers how stimulus, noise masking and recording parameters affect the frequency and place specificity of auditory brainstem responses (ABRs) to air- and bone-conducted stimuli. Issues concerning the use of clicks for ABR threshold estimates will first be presented, followed by results for tone-evoked ABR thresholds and how well they predict the pure-tone behavioral audiogram. Noise-masking options (e.g. high-pass noise, notched noise and white noise) to improve the frequency specificity of tone-evoked ABRs, which are now available on clinical ABR units, will also be discussed. The goal of this article is to demonstrate that ABRs to tonal stimuli can be successfully recorded in most clinical environments and can provide reasonably accurate estimates of 500- to 4000-Hz pure-tone behavioral thresholds in infants, children and adults. Specific parameters and protocols for obtaining frequency-specific ABR threshold responses are provided.

The effects of decreased audibility produced by high-pass noise masking on cortical event-related potentials to speech sounds/ba/and/da.

This study investigated the effects of decreased audibility produced by high-pass noise masking on cortical event-related potentials (ERPs) N1, N2, and P3 to the speech sounds /ba/and/da/presented at 65 and 80 dB SPL. Normal-hearing subjects pressed a button in response to the deviant sound in an oddball paradigm. Broadband masking noise was presented at an intensity sufficient to completely mask the response to the 65-dB SPL speech sounds, and subsequently high-pass filtered at 4000, 2000, 1000, 500, and 250 Hz. With high-pass masking noise, pure-tone behavioral thresholds increased by an average of 38 dB at the high-pass cutoff and by 50 dB one octave above the cutoff frequency. Results show that as the cutoff frequency of the high-pass masker was lowered, ERP latencies to speech sounds increased and amplitudes decreased. The cutoff frequency where these changes first occurred and the rate of the change differed for N1 compared to N2, P3, and the behavioral measures. N1 showed gradual changes as the masker cutoff frequency was lowered. N2, P3, and behavioral measures showed marked changes below a masker cutoff of 2000 Hz. These results indicate that the decreased audibility resulting from the noise masking affects the various ERP components in a differential manner. N1 is related to the presence of audible stimulus energy, being present whether audible stimuli are discriminable or not. In contrast, N2 and P3 were absent when the stimuli were audible but not discriminable (i.e., when the second formant transitions were masked), reflecting stimulus discrimination. These data have implications regarding the effects of decreased audibility on cortical processing of speech sounds and for the study of cortical ERPs in populations with hearing impairment.

Frequency specificity of the human auditory brainstem and middle latency responses to brief tones. I. High-pass noise masking.

This study investigated the frequency specificity of the auditory brainstem (ABR) and middle latency (MLR) responses to 500- and 2000-Hz brief tones using high-pass noise masking. Stimuli were linear- (2-1-2 cycles) and exact-Blackman- (5 cycles) gated tones presented at 80 dB peak-to-peak equivalent (ppe) SPL. Cochlear contributions to ABR wave V-V' and MLR wave Na-Pa were assessed by the effects of high-pass noise masking on response amplitudes and latencies. The high-pass noise results demonstrate that the ABR and the MLR to the 80 dB ppe SPL brief tones show good frequency and place specificity. Changes in ABR or MLR amplitude and latency with high-pass noise masking did not occur as the masker cutoff was decreased from 2 to 3 octaves above the stimulus nominal frequency until it was within one-half octave of this frequency, below which amplitudes rapidly decreased (500- and 2000-Hz tones) and latencies increased (500-Hz tones). No significant differences existed in the frequency specificity of the ABR versus MLR, or in these evoked potentials to exact-Blackman- versus linear-gated tones.

Frequency specificity of the human auditory brainstem and middle latency responses to brief tones. II. Derived response analyses.

This study investigated the frequency specificity of the auditory brainstem (ABR) and middle latency (MLR) responses to 500- and 2000-Hz brief tones using narrow-band derived response analyses of the responses recorded in high-pass masking noise [Oates and Stapells, J. Acoust. Soc. Am. 102, 3597-3608 (1997)]. Stimuli were linear- and exact-Blackman-gated tones presented at 80 dB ppe SPI. Cochlear contributions to ABR wave V-V' and MLR wave Na-Pa were assessed by response amplitude profiles as a function of derived band center frequency. The largest amplitudes of waves V and Na-Pa occurred in the 500- and 707-Hz derived bands in response to the exact-Blackman- and linear-gated 500-Hz tones. The peak in the response amplitude profiles for wave V to both 2000-Hz stimuli was seen in the 2000-Hz derived band. For wave Na-Pa, the maxima in the amplitude profiles occurred in the 2000- and 1410-Hz derived bands for the exact-Blackman- and linear-gated tones. Smaller cochlear contributions to the ABR/MLR were also present at 0.5-1 octave above and below the nominal stimulus frequencies. The ABR/MLR to 500- and 2000-Hz 80 dB ppe SPL tones thus shows good frequency specificity, with no significant differences in the frequency specificity of: (1) ABR versus MLR; (2) these evoked potentials to 500-versus 2000-Hz tones; and (3) responses to exact-Blackman- versus linear-gated tones.

Frequency-specific identification of hearing loss using transient-evoked otoacoustic emissions to clicks and tones.

Transient-evoked otoacoustic emissions (TEOAE) to clicks and to 500- and 2000-Hz brief tones were measured in 72 normal-hearing and hearing-impaired subjects (86 ears). The TEOAE's reproducibility parameter was used for the analyses. The purpose of the investigation was to determine which stimuli best predicted the presence of sensorineural hearing loss in a frequency-specific manner at 500, 1000, 2000, and 4000 Hz. Analyses of the TEOAEs filtered into frequency-specific bands showed that separation of normal and impaired ears at 1000, 2000 and 4000 Hz was best achieved by TEOAEs evoked by clicks. Identification of hearing loss at 500 Hz was best obtained using 500-Hz tone-evoked TEOAEs filtered using a band centered at 500 Hz. Octave- and half-octave-wide bands identified hearing loss equally well. An analysis sweep time of 20 ms provided slightly better results compared to 30 ms, except for 500 Hz, where the 30-ms sweep time slightly improved the identification of hearing loss. Increases in the audiometric criterion did not yield better test performance once hearing loss exceeded 20 dB HL. The findings from this study suggest that the combination of bandpass-filtered TEOAEs to clicks and TEOAEs to 500-Hz tones identifies with reasonable accuracy ears with sensorineural hearing loss at 500, 1000, 2000, and 4000 Hz.

Electrophysiologic manifestations of impaired temporal lobe auditory processing in verbal auditory agnosia.

The present study examined the extent to which verbal auditory agnosia (VAA) is primarily a phonemic decoding disorder, as contrasted to a more global defect in acoustic processing. Subjects were six young adults who presented with VAA in childhood and who, at the time of testing, showed varying degrees of residual auditory discrimination impairment. They were compared to a group of young adults with normal language development matched for age and gender. Cortical event-related potentials (ERPs) were recorded to tones and to consonant-vowel stimuli presented in an "oddball" discrimination paradigm. In addition to cortical ERPs, auditory brainstem responses (ABRs) and middle latency responses (MLRs) were recorded. Cognitive and language assessments were obtained for the VAA subjects. ABRs and MLRs were normal. In comparison with the control group, the cortical ERPs of the VAA subjects showed a delay in the N1 component recorded over lateral temporal cortex both to tones and to speech sounds, despite an N1 of normal latency overlying the frontocentral region of the scalp. These electrophysiologic findings indicate a slowing of processing of both speech and nonspeech auditory stimuli and suggest that the locus of this abnormality is within the secondary auditory cortex in the lateral surface of the temporal lobes.

Thresholds for auditory brain stem responses to tones in notched noise from infants and young children with normal hearing or sensorineural hearing loss.

OBJECTIVE: To assess the accuracy of threshold estimates determined using the auditory brain stem responses (ABRs) to brief tones presented in notched noise in a group of infants and young children with normal hearing or sensorineural hearing loss (SNHL). DESIGN: The thresholds for ABRs to brief duration 500, 2000, and 4000 Hz tones presented in notched-noise masking were evaluated in infants and young children with normal hearing (N = 34) or SNHL (N = 54). Tone-evoked ABR thresholds were compared with behavioral thresholds obtained at follow-up audiologic assessments, for a total of 220 comparisons. RESULTS: ABR thresholds for the infants with bilateral normal hearing were 23.6, 12.9, and 12.6 dB nHL for 500, 2000 and 4000 Hz, respectively. Most (92 to 100%) infants with normal hearing showed ABRs to 30 dB nHL tones. Across all subjects (i.e., those with normal hearing and those with impaired hearing), high ( > or = 0.94) correlations were found between the ABR and behavioral thresholds. The mean differences between ABR (dB nHL) and behavioral (dB HL) thresholds across all subjects were 8.6, -0.4, and -4.3 dB for 500, 2000, and 4000 Hz, respectively. Overall, 98% of the ABR thresholds were within 30 dB of the behavioral thresholds, 93% were within 20 dB, and 80% were within 15 dB. CONCLUSIONS: These threshold results for the ABR to brief tones in notched noise obtained for infants and young children are similar to those obtained in similar studies of adults. The technique may be used clinically with reasonable accuracy to estimate pure-tone behavioral thresholds in infants and young children who are referred for diagnostic threshold ABR testing.

Pure-tone masking profiles for human auditory brainstem and middle latency responses to 500-Hz tones.

A simultaneous masking paradigm was used to determine the frequency selectivity of human auditory brainstem (ABR) and middle latency (MLR) responses to 60 dB pe SPL 500-Hz probe tones in 12 normal adults. Masking profiles for simultaneous recordings of the ABR and MLR were obtained in the presence of pure-tone maskers presented at 60- and 70-dB SPL. Results show sharp amplitude profiles with maximum reduction in amplitude seen using the 500-Hz maskers. There were no significant differences in the masking profiles for the ABR and MLR waves to the 500-Hz probe tones. An additional measure of frequency selectivity, bandwidth at 50% reduction in amplitude (W50), also demonstrated no significant difference between the ABR and MLR waves. In summary, the results of this study and those of an earlier study (Mackersie et al., 1993) suggest no significant difference in the frequency selectivity of the ABR and MLR to low-intensity (60 dB pe SPL) 500- and 2000-Hz tones.

Auditory Brainstem Response Wave I Prediction of Conductive Component in Infants and Young Children.

Wave I latencies were used to predict the magnitude of conductive components in 80 infants and young children (122 ears) with normal hearing, conductive hearing loss due to otitis media or aural atresia, sensorineural hearing loss, and mixed hearing loss. Two prediction methods were used. The first method based predictions on a 0.03-ms wave I latency delay for each decibel of conductive hearing loss. The second method was based on a regression analysis of wave I latency delays and the magnitude of conductive component for the subjects in this study with normal cochlear status. On average, these prediction methods resulted in prediction errors of 15 dB or greater in over one-third of the ears with hearing loss. Therefore, the clinical use of wave I latencies to predict the presence or magnitude of conductive impairment is not recommended for infants and young children. Instead, bone-conduction ABR testing is recommended as a direct measure of cochlear status when behavioral evaluation is not possible.

Behavioral, electrophysiologic, and otoacoustic measures from a child with auditory processing dysfunction: case report.

This case was selected to highlight the importance of the test battery approach in the assessment of a child with auditory processing deficits. The utility of behavioral, electrophysiologic, acoustic immittance, and evoked otoacoustic emission procedures, as well as the problems associated with interpreting these multiple measures with differing results, is discussed. This case was confounded by the possibility that both peripheral and central auditory problems existed. The outcome stresses the importance of examining the results of multiple auditory measures in the determination of the site of lesion and habilitation strategies.

Pure-tone masking profiles for human auditory brainstem and middle latency responses.

Several studies have compared the frequency selectivity of waves I and V of the auditory brainstem response (ABR) in humans, however little is known about the frequency selectivity of the middle latency response (MLR). Simultaneous recordings of ABRs and MLRs to 60 dB peSPL 2000-Hz probe tones were obtained in the presence of 0.5, 1.0, 1.41, 2.0, 2.83 and 4.0 kHz maskers presented at 40, 60, and 80 dB SPL. ABR/MLR iso-intensity masking profiles showing the percentage of the unmasked amplitudes as a function of frequency were constructed for ABR peak V-Vn and MLR peaks Na-Pa and Nb-Pb at each masker intensity. No significant differences were found between the frequency selectivity of the ABR and MLR, and the effects of masking on the amplitudes of these responses were similar. These results are consistent with the suggestion that frequency tuning is similar up to the level of the primary auditory cortex.

Normal infant and adult auditory brainstem responses to bone-conducted tones.

Auditory brainstem responses (ABRs) were recorded to 500- and 2000-Hz bone-conducted (BC) tones from normal infants and adults. Infant ABR thresholds for the 500-Hz BC tones are significantly lower than their thresholds to 2000-Hz BC tones. Infant wave V latencies to 500-Hz BC tones are significantly shorter than those of adults, whereas infant and adult responses to 2000-Hz BC tones are similar in latency, suggesting that the effective intensity of the BC tones may be 9-17 dB greater for infants than for adults. A marked asymmetry between the ipsilaterally and contralaterally recorded wave V is seen for infant responses to 500- and 2000-Hz tones at all intensities; this asymmetry is not as evident in adults, except near threshold.

Transient evoked otoacoustic emissions: clinical applications and technical considerations.

Otoacoustic emissions are defined as sound energy emitted by the cochlea. They are believed to be generated by the outer hair cells of the Organ of Corti. Several types of evoked otoacoustic emissions have been described. At present, transient-evoked otoacoustic emissions (TEOAEs) equipment is readily available commercially for clinical purposes. This paper describes our early experience with this equipment from a clinician's perspective. It reviews some of the technical problems we have encountered and their solutions. It also presents selected clinical examples where TEOAEs were particularly helpful in the clinical setting, thus illustrating the potential usefulness of this new clinical tool.

Frequency specificity of the auditory brain stem response to bone-conducted tones in infants and adults.

Auditory brain stem responses were obtained from normal-hearing infants and adults in response to bone-conducted 500 and 2000 Hz tones presented in quiet and high-pass noise masking. The tones were presented at 70 (500 and 2000 Hz) and 46 (2000 Hz) dB peak to peak equivalent (re: 1 dyne RMS). The high-pass noise-masked waveforms were subtracted in succession to obtain derived responses, providing estimates of the cochlear regions contributing to the nonmasked responses. Findings indicate that the auditory brain stem response to bone-conducted 500 Hz tones is frequency specific for both infants and adults. For 2000 Hz tones, the results show maximum amplitudes for cochlear regions representing the nominal frequency of the tone for adults. For infants, maximum response amplitudes for the derived responses to 2000 Hz, 70 dB tones were obtained within 1/2 octave of the nominal frequency (1410-2000 Hz). Wave V latencies of the derived responses are similar for both groups for 2000 Hz tones, but shorter for infants to 500 Hz tones, supporting the hypothesis that low-frequency bone-conducted stimuli are effectively more intense in infants than adults.

Interaction of click intensity and cochlear hearing loss on auditory brain stem response wave V latency.

Auditory brain stem responses (ABRs) to 95, 80, 60, 40, and 30 dB nHL clicks were retrospectively studied from 103 patients (194 ears) with various degrees of cochlear impairment. Hearing loss and sample size were balanced across gender. Results indicate that the slope of the wave V latency versus 4000 Hz hearing loss function doubles as click intensity is decreased from 80 (0.01 msec/dB HL) to 60 nHL (0.02 msec/dB HL). Overall results indicate a slope increase of 0.0004 msec for each decibel decrease in click intensity from 95 to 30 dB nHL. Intersubject variability increased with increased hearing loss and/or decreased stimulus intensity. The effects of hearing loss on wave V latency are minimal, and intersubject variability is less if high-intensity clicks (greater than or equal to 95 dB nHL) are used. No differences in the effects of hearing loss on wave V latency were seen between males and females. Latency corrections for cochlear hearing loss should, therefore, consider stimulus intensity.

Evoked potential assessment of auditory system integrity in infants.

One child in 750 is born with a handicapping hearing impairment. The methods available to screen and evaluate infants at risk (auditory brainstem responses, middle latency responses, and cortical auditory evoked potentials) are reviewed, explained, and illustrated with case histories.