Maturation of bone conduction multiple auditory steady-state responses

Assessment of Interaural Attenuation in Infants and Young Children Using Bone-Conducted Auditory Brainstem Response

OBJECTIVES

In hearing assessment, the term interaural attenuation (IAA) is used to quantify the reduction in test signal intensity as it crosses from the side of the test ear to the nontest ear. In the auditory brainstem response (ABR) testing of infants and young children, the size of the IAA of bone-conducted (BC) stimuli is essential for the appropriate use of masking, which is needed for the accurate measurement of BC ABR thresholds. This study aimed to assess the IAA for BC ABR testing using 0.5 to 4 kHz narrowband (NB) CE-chirp LS stimuli in infants and toddlers with normal hearing from birth to three years of age and to examine the effects of age and frequency on IAA.

DESIGN

A total of 55 infants and toddlers with normal hearing participated in the study. They were categorized into three age groups: the young group (n = 31, infants from birth to 3 mo), middle-aged group (n = 13, infants aged 3-12 mo), and older group (n = 11, toddlers aged 12-36 mo). The participants underwent BC ABR threshold measurements for NB CE-chirp LS stimuli at 0.5 to 4 kHz. For each participant, one ear was randomly defined as the "test ear" and the other as the "nontest ear." BC ABR thresholds were measured under two conditions. In both conditions, traces were recorded from the channel ipsilateral to the test ear, whereas masking was delivered to the nontest ear. In condition A, the bone oscillator was placed on the mastoid of the test ear, whereas in condition B, the bone oscillator was placed on the mastoid contralateral to the test ear. The difference between the thresholds obtained under conditions A and B was calculated to assess IAA.

RESULTS

The means of IAA (and range) in the young age group for the frequencies 0.5, 1, 2, and 4 kHz were 5.38 (0-15) dB, 11.67 (0-30) dB, 21.15 (10-40) dB, and 23.53 (15-35) dB, respectively. Significant effects were observed for both age and frequency on BC IAA. BC IAA levels decreased with age from birth to 36 mo. In all age groups, smaller values were observed at lower frequencies and increased values were observed at higher frequencies.

CONCLUSIONS

BC IAA levels were both age and frequency dependent. The study found that the BC IAA values for lower stimulus frequencies were smaller than previously assumed, even in infants younger than 3 mo. These results suggest that masking should be applied in BC ABR threshold assessments for NB CE-chirp LS stimuli at 0.5, 1, and 2 kHz, even in young infants. Masking may not be necessary for testing at 4 kHz if a clear response is obtained at 15 dB normal-hearing level (nHL) in infants younger than 3 mo.

Bone Conduction: Benefits and Limitations of Surgical and Nonsurgical Devices

Bone conduction devices (BCDs) are a well-established and effective treatment solution for children with conductive and mixed hearing loss. Evidence indicates that early intervention through BCDs can improve hearing, speech, and language, and developmental outcomes. BCDs overcome several limitations associated with traditional hearing aids, and in many cases offer children an alternative to more invasive surgical management. Despite these benefits, children with conductive hearing loss are often subject to delays in intervention. In addition, interventional challenges and technological limitations of BCDs prevent widespread adoption and acceptance, particularly in early childhood.

Transcranial attenuation in bone conduction stimulation

In bone conduction (BC) stimulation, the sound travels from the site of stimulation to the ipsilateral and contralateral cochlea. A frequency dependent reduction in BC hearing sensitivity occurs when sound travels to the contralateral cochlea as compared to the ipsilateral cochlea. This effect is called transcranial attenuation (TA) that is affected by several factors. Experimental and clinical studies describe TA and the factors that have an effect on it. These factors include stimulus location, coupling of a bone conduction hearing aid to the underlying tissue, and the properties of the head (such as geometry of the head, thickness of the skin and/or skull, changes due to aging, iatrogenic changes such as bone removal in mastoidectomy, and occlusion of the external auditory canal). While TA has an effect of the patient's benefit of BCHAs, there seems to be a discrepancy between experimental measurements and clinical relevance. The effects are small and the interindividual variability, in comparison, is rather large. However, a better understanding of these factors may help to determine the site of attachment, the coupling mode, and possibly the fitting of a BCHA, depending on its indication.

Effective Masking Levels for Bone Conduction Auditory Brainstem Response Stimuli in Infants and Adults with Normal Hearing

OBJECTIVE

The purpose of the present study was to investigate effective masking levels (EMLs) for bone conduction (BC) auditory brainstem response (ABR) testing in infants and adults. Early hearing detection and intervention programs aim to limit delays in identifying ear-specific type/degree of hearing loss in infants using the ABR. Ear-specific assessment poses challenges as sound delivered to one ear can travel across the skull and activate the contralateral cochlea. Wave V amplitude and latency measures ipsilateral and contralateral to the bone oscillator can be compared to isolate the test cochlea in some cases; however, when these findings are equivocal, clinical masking is required. This study aims to determine EMLs for ABRs elicited to 500- and 2000-Hz BC stimuli for normal-hearing infants (0 to 18 months) and adults.

DESIGN

Participants were 21 adults (18 to 54 years) and 24 infants (5 to 47 weeks) with normal hearing. BC 500- and 2000-Hz brief tonal stimuli at intensities approximating normal levels were presented via a B-71 oscillator (infants: 20 dB nHL at 500 Hz and 30 dB nHL at 2000 Hz; adults: 500 and 2000 Hz at 20 and 30 dB nHL, respectively). White noise masking was presented binaurally via ER-3A earphones (22 to 82 dB SPL; 10-dB steps). The lowest level of masking to eliminate a BC response was deemed the EML.

RESULTS

For stimuli presented at 20 dB nHL, adult mean (1 SD) EMLs for 500 and 2000 Hz were 65 (9) and 53 (6) dB SPL, respectively. Mean EMLs for infants were 80 (6) dB SPL for 500 Hz at 20 dB nHL and 64 (9) dB SPL for 2000 Hz at 30 dB nHL. Compared to adults, infants required approximately 13 dB more masking at 500 Hz but a similar amount of masking at 2000 Hz. Infants required 26 dB more masking at 500 versus 2000 Hz, whereas, adults required only 12 dB more masking.

CONCLUSIONS

Maximum binaural EMLs for infant BC responses elicited to 500 Hz at 20 dB nHL are 82 dB SPL, and for 2000 Hz at 30 and 40 dB nHL, respectively, are 72 and 82 dB SPL. Monaural masking levels for the nontest ear (assuming 10 dB of interaural attenuation) recommended clinically are as follows: (1) 500 Hz: 72 and 82 dB SPL at 20 and 30 dB nHL, respectively; and (2) 2000 Hz: 62, 72, and 82 dB SPL at 30, 40, and 50 dB nHL, respectively. Unsafe levels of white noise would be needed to effectively mask at greater stimulus levels.

Using auditory steady-state responses for measuring hearing protector occlusion effect

INTRODUCTION

The currently available methods for measuring the occlusion effect (OE) of hearing protection devices (HPDs) have limitations. Objective microphonic measurements do not assess bone-conducted sounds directly transmitted to the cochlea. Psychophysical measurements at threshold are biased due to the low-frequency masking effects from test participants' physiological noise and the variability of measurements based on subjective responses. An auditory steady-state responses (ASSRs) procedure is used as a technique that might overcome these limitations.

PARTICIPANTS AND METHODS

Pure-tone stimuli (250 and 500 Hz), with amplitude modulated at 40 Hz, were presented to twelve adults with normal hearing through a bone vibrator at three levels in 10-dB steps. The following two conditions were assessed: the unoccluded ear canal and occluded ear canal. ASSR amplitude data as a function of the stimulation level were linearized using least-square regressions. The ASSR-based "physiological" OE was then calculated as the average difference between the two measurements.

RESULTS

A significant statistical difference was found between the average threshold-based psychophysical OE and the average ASSR-based OE.

CONCLUSION

This study successfully ascertained that it is possible to objectively measure the OE of HPD using ASSRs collected on the same participant both with and without protectors.

Provisional stimulus level corrections for low frequency bone-conduction ABR in babies under three months corrected age

OBJECTIVE

To estimate bone-conduction stimulus level corrections by testing the auditory brainstem response (ABR) of normally-hearing newborns. The stimuli used were low frequency tone pips calibrated to reference levels derived from ISO 389 values.

DESIGN

Tone pips were presented via supra-aural earphones and a B71 Radioear bone vibrator at 0.5 or 1 kHz. ABR thresholds from both transducers were compared at each frequency.

STUDY SAMPLE

twenty-seven newborn hearing screening referrals (33 ears) who passed an ABR discharge criterion at 4 kHz.

RESULTS

Median air- and bone-conduction ABR threshold differences were 30 dB at 0.5 kHz and 20 dB at 1 kHz.

CONCLUSION

The 0.5 kHz data from this study and previous studies were compared. Previous studies suggested lower figures for the bone-conduction stimulus level correction. Likely sources of this discrepancy are discussed. The average 0.5 kHz bone-conduction correction value for infants < 3 months old is about 28 dB. The correction for 1 kHz is 20 dB. We recommend that calibration reference levels used in this study be adopted and that appropriate corrections be applied to bone conduction ABR thresholds in infants < 3 months old before calculation of any air-bone gap and subsequent clinical interpretation.

Auditory brainstem responses to bone-conducted brief tones in young children with conductive or sensorineural hearing loss

The bone-conduction (BC) tone ABR has been used clinically for over 20 years. The current study formally evaluated the test performance of the BC tone-evoked ABR in infants with hearing loss. Method. By comparing BC-ABR results to follow-up behavioural results, this study addressed two questions: (i) whether the BC tone ABR was successful in differentiating children with conductive versus sensorineural hearing loss (Study A; conductive: 68 ears; SNHL: 129 ears) and (ii) the relationship between BC ABR and behavioural hearing loss severity (Study B: 2000 Hz: 104 ears; 500 Hz: 47 ears). Results. Results demonstrate that the "normal" BC-ABR levels accurately differentiated normal versus elevated cochlear sensitivity (accuracy: 98% for 2000 Hz; 98% for 500 Hz). A subset of infants in Study A with elevated BC-ABR (i.e., no response at normal level) had additional testing at higher intensities, which allowed for categorization of the degree of cochlear impairment. Study B results indicate that the BC ABR accurately categorizes the degree of cochlear hearing loss for 2000 Hz (accuracy = 95.2%). A preliminary dBnHL-to-dBHL correction factor of "0 dB" was determined for 2000 Hz BC ABR. Conclusions. These findings further support the use of BC tone ABR for diagnostic ABR testing.

Effective masking levels for bone conduction auditory steady state responses in infants and adults with normal hearing

OBJECTIVE

To obtain ear-specific bone conduction thresholds, masking of the nontest ear is often required. Bone conduction masking has not been formally investigated for infants assessed physiologically. The objective of this study was to determine effective masking levels (EMLs) for auditory steady state responses (ASSRs) elicited by bone-conducted stimuli in a group of normal-hearing infants and adults.

DESIGN

Participants were 15 infants younger than 6 mo and 15 adults, all with normal hearing. EML was defined as the lowest level of a binaural air-conducted masker that resulted in absent bone conduction ASSRs. Stimuli were single bone-conducted tones that were 100% amplitude modulated and 25% frequency modulated at 85 and 101 for 1000 and 4000 Hz, respectively. The stimuli were calibrated in dB HL (ANSI S3.6-1996) and expressed in dB HL or dB SL (dB relative to mean bone conduction ASSR thresholds reported in a previous study). The maskers were 1 and 4 kHz narrowband noise generated by a clinical audiometer. Unmasked and masked ASSRs were obtained for each participant. Real ear-to-coupler differences (RECDs) were also obtained for each participant and were used to convert masker dB SPL measured in the coupler to dB SPL in the individual ear canal.

RESULTS

Infant EMLs for ASSRs elicited to bone-conducted stimuli in dB HL were 6 to 7 dB higher and 8 to 10 dB lower for 1000 and 4000 Hz, respectively, compared with adults. When masker was adjusted for RECDs, infant EMLs were 12 dB higher at 1000 Hz and similar at 4000 Hz compared with adults. When the stimulus levels were corrected for the mean differences in ASSR bone conduction thresholds between infants and adults and the masker levels adjusted for RECDs, infants had lower EMLs at 1000 Hz and equal EMLs at 4000 Hz, in comparison to adults. Frequency- and level-dependent effects on ASSR amplitude due to masking were found and differed between infants and adults.

CONCLUSIONS

Our findings indicate that there are frequency- and level-dependent infant-adult differences in EMLs for bone conduction ASSRs and confirm that a 1000 Hz stimulus is 12 dB more effective for infants compared with adults. The following infant preliminary masking levels for bone conduction stimuli are recommended: (i) 1000 Hz: 48 and 58 dB SPL at 15 and 25 dB HL, respectively, and (ii) 4000 Hz: 40 and 45 dB SPL at 25 and 35 dB HL, respectively.

The efficiency of the single- versus multiple-stimulus auditory steady state responses in infants

OBJECTIVES

Multiple auditory steady state responses (ASSRs) will likely be included in the diagnostic test battery for estimating infant auditory thresholds in the near future; however, the effects of single- versus multiple-stimulus presentation in infants has never been investigated. In adults, there are no interactions (reduced amplitudes) between responses to multiple simultaneous stimuli presented at 60 dB SPL or lower. Maturational differences, however, may lead to greater interactions in infants; thus, it is unknown whether the single-stimulus technique or the multiple-stimulus technique is more efficient for testing infants. Two studies were carried out to address this issue.

DESIGN

All infants in study A participated in three stimulus conditions, which differed in the number of stimuli presented simultaneously. The monotic single (MS) condition consisted of 500, 1000, 2000, and 4000 Hz tones, which were presented singly to one ear. The monotic multiple (MM) condition was composed of four tones (500, 1000, 2000, and 4000 Hz) presented to one ear simultaneously. The dichotic multiple (DM) condition consisted of eight tones presented simultaneously to both ears (four tones to each ear). ASSR amplitudes were obtained from 15 normal infants (mean age: 23.1 wks) in response to multiple (MM, DM) and single (MS) air conduction amplitude-modulated (AM) tones (77 to 105 Hz modulation rates; 60 dB SPL). In study B, ASSR thresholds were determined for 500-Hz stimuli in the single- and DM-stimulus conditions (14 infants; mean age: 20.2 wks).

RESULTS

Mean single-stimulus ASSR amplitudes for 500, 1000, 2000, and 4000 Hz were 30, 39, 45 and 43 nV, respectively. Presentation of multiple AM tones (i.e., four octave-spaced frequencies) to one ear resulted in ASSR amplitudes that were 97%, 87%, 82%, and 70% (for 500, 1000, 2000, and 4000 Hz, respectively) of the single-stimulus ASSR amplitudes. Results for the dichotic presentation of eight AM tones show ASSR amplitudes that were 70%, 77%, 67%, and 67% relative to the MS condition. Although decreases in amplitude occurred using multiple stimuli in infants, the multiple ASSR remained more efficient than the single-stimulus ASSR (i.e., multiple-stimulus amplitudes were greater than single-stimulus amplitudes divided by √K, where K is the number of stimuli). Results from study B indicate that ASSR thresholds for 500 Hz presented in the DM condition were elevated 3 dB compared with that obtained in the 500-Hz single-stimulus condition. This statistically nonsignificant difference is within the range of acceptable test-retest variability and is thus not of clinical significance.

CONCLUSIONS

The amplitude reductions seen in the multiple-stimulus conditions in infants, not seen in adults, could be related to maturational differences in the ear canal, middle ear, cochlea, and/or brain stem. Because greater interactions occur in the DM-stimulus condition compared with the monotic multiple-stimulus condition and baseline single-stimulus condition, brain stem origins of these interactions are likely. Study B revealed statistically nonsignificant differences between threshold for 500 Hz when presented in the single- and DM-stimulus conditions. In summary, as with adults, multiple-stimulus presentation in infants is more efficient than single AM tones, at least for 60 dB SPL stimuli.

Multiple auditory steady state response thresholds to bone conduction stimuli in adults with normal and elevated thresholds

OBJECTIVE

Auditory steady state responses (ASSRs) to multiple air conduction (AC) stimuli modulated at ∼80 Hz have been shown to provide reasonable estimates of the behavioral audiogram. To distinguish the type of hearing loss (i.e., conductive, sensorineural, or mixed), bone conduction (BC) results are necessary. There are few BC-ASSR data, especially for individuals with hearing loss. The present studies aimed to (1) determine multiple ASSR thresholds to BC stimuli in adults with normal hearing, masker-simulated hearing loss, and sensorineural hearing loss (SNHL) and (2) determine how well BC-ASSR distinguishes normal versus elevated thresholds to BC stimuli in adults with normal hearing or SNHL.

DESIGN

Multiple ASSR and behavioral thresholds for BC stimuli were determined in two studies. Study A assessed 16 normal-hearing adults with relatively flat threshold elevations produced by 50, 60, and 70 dB SPL AC masking noise, as well as no masking. Study B assessed 10 adults with normal hearing and 40 adults with SNHL. In both studies, the multiple (500 to 4000 Hz) ASSR stimuli were modulated between 77 and 101 Hz and varied in intensity from 0 to 50 dB HL in 10-dB steps. Stimuli were presented using a B71 bone oscillator held on the temporal bone by an elastic band while participants relaxed or slept.

RESULTS

Study A: Correlations (r) between behavioral and ASSR thresholds for all conditions combined were 0.77, 0.87, 0.90, and 0.87 for 500, 1000, 2000, and 4000 Hz, respectively. ASSR minus behavioral threshold difference scores for all frequencies combined for the no-masker, 50, 60, and 70 dB SPL masker conditions were 14.3 ± 9.2, 12.1 ± 10.4, 12.7 ± 7.7, and 11.4 ± 8.1 dB, respectively. Study B: The difference scores for 500, 1000, 2000, and 4000 Hz were, on average, 15.7 ± 12.3, 10.3 ± 10.7, 9.7 ± 10.3, and 5.7 ± 7.9 dB, respectively, with correlations of 0.73, 0.84, 0.87, and 0.94 for the normal-hearing and SNHL groups combined. The ASSR minus behavioral difference scores were significantly larger for 500 Hz and significantly smaller for 4000 Hz compared with 1000 and 2000 Hz. Across all frequencies, the BC-ASSR correctly classified 89% of thresholds as "normal" or "elevated" (92% correct for 1000, 2000, and 4000 Hz).

CONCLUSIONS

The threshold difference scores and correlations in individuals with SNHL are similar to those in normal listeners with simulated SNHL. These difference scores are also similar to those shown by previous studies for the AC-ASSR in individuals with SNHL, at least for 1000 to 4000 Hz. The BC-ASSR provides a reasonably good estimate of BC behavioral threshold in adults, especially between 1000 and 4000 Hz. Further research is required in infants with hearing loss.

Bone-conducted hearing assessment with 80-Hz multiple auditory steady-state responses to brief tones in adults with normal hearing

OBJECTIVE

To investigate interactions (if any) in the bone-conduction auditory steady-state response (BC ASSR) between multiple brief tones presented simultaneously.

METHODS

500-, 1,000-, 2,000-, and 4,000-Hz brief tones, repeated at a rate of 77-101 Hz, were presented using a B-71 vibrator. BC ASSR thresholds and amplitudes at 50 dB nHL were measured in two conditions where the stimulus was either presented alone or together with other stimuli.

RESULTS

Significantly larger amplitudes in the single-stimulus condition were found at 50 dB nHL. However, there was no significant threshold difference between single- and multiple-stimulus conditions. The BC ASSR thresholds (means ± SD) at 500, 1,000, 2,000, and 4,000 Hz were 96.7 ± 9.7, 75.3 ± 11.5, 65.6 ± 7.4, and 57.8 ± 7.2 dB re 1 μN ppe, respectively.

CONCLUSION

Interactions occurred in the multiple-stimulus condition at high presentation levels, but not at threshold levels. The results of the present study imply that BC ASSR thresholds to multiple brief-tone stimuli can be assessed at the same time, at least in normal-hearing adults.