This detailed research article describes the study of electrophysiological hearing thresholds using the Interacoustics Eclipse EP system in 102 infants and toddlers (58F 44M), where 59% were 5 months or younger at the time of assessment. Sininger states the objectives of the study was to compare the predicted audiometric thresholds obtained by ASSR and ABR in this sample when both techniques use optimal stimuli and detection algorithms. The stated aim was to address the past discrepancies studies found between ABR and first generation ASSR measures. The second objective of Sininger’s team was to determine and compare test times required by the 2 techniques to predict thresholds for both ears at the 4 audiometric frequencies of 0.5, 1.0, 2.0, and 4.0 KHz. The data for determined thresholds within the study was evaluated by Sininger and correction factors applied. The findings of the study demonstrated thresholds were significantly lower for ASSR than ABR, and showed greatest difference at 0.5 and1.0KHz, with up to 14 dBnHL lower thresholds being detected using ‘next generation’ detection when compared to ABR using an automated response detection (FMP). The improvement in ASSR threshold detection was attributed to the advances implemented in the Eclipse EP system for response detection utilising information at multiple harmonics of the modulation frequency. The stimulation paradigm which utilised NB CE-Chirp also contributed to the lower absolute levels in nHL. The research clinicians in this study obtained all 8 thresholds in one appointment in 83% of ABR, and 87% ASSR assessments. Within the study participants 49% had thresholds determined as normal by ASSR and ABR. The time to obtain 8 frequency specific thresholds for these infants was 24.02 mins for ABR, and 15.31 mins for ASSR. The features of the Eclipse EP system that the authors call ‘next generation’ detection when compared to the first generation ASSR measures, are summarised as the assessment of 12 harmonics, rather than 1, and the use of both phase and amplitude information, rather than one or the other, as well as careful calculation of appropriate test criterion. This study demonstrates that ASSR using the eclipse is now a suitable alternative as well as a quicker test to perform than ABR in measuring hearing threshold in infants.
Provisional stimulus level corrections for low frequency bone-conduction ABR in babies under three months corrected age.
Frequency-specific ABR testing in infants and newborns via air-conduction (AC) is commonplace in the clinic. In cases when AC thresholds are elevated, it may be necessary to obtain additional results via bone-conduction (BC) to determine if the hearing loss is conductive or sensorineural. However, calibration of stimuli for these tests are typically referenced for adults. Newborns present challenges to BC calibration due to smaller and unfused cranial plates. Additionally, calibration of BC transducers are referenced to artificial mastoids that simulate adult mastoids. This study estimates the necessary BC stimulus corrections (relative to adults) at 500 and 1000 Hz from 27 normal-hearing newborns via a B71 and TDH39 transducers. Median age-related BC stimulus corrections for babies under 3 months of age are 30 dB at 500 Hz and 20 dB at 1000 Hz. These results emphasize the importance of correcting BC stimulus level for newborns when performing BC ABR testing.
The auditory brainstem response (ABR) is an integral clinical metric for the estimation of hearing threshold, assessment of the neurological integrity of the auditory system, and most commonly, screening for hearing loss in newborns and babies. However, the ABR response can be constrained by low signal-to-noise ratios (SNR) precluding accurate and reliable responses. Artefact rejection (AR) is one technique used to improve the SNR by allowing signal averaging to continue only if the peak amplitude of the response is below a defined limit. The current study investigates the effect of Bayesian weighting and AR level upon the efficiency of noise reduction across 26 babies referred from the English Newborn Hearing Screening program. ABR recordings using an Interacoustics Eclipse were evaluated for 5 AR levels and 2 AR levels with Bayesian averaging. Strict AR levels are optimal when noise is low; whereas, more lenient AR levels are more efficient when noise is high. Bayesian averaging can facilitate increased efficiency as noise levels increase. This suggests that the use of Bayesian weighting available in the Eclipse offers additional efficiency for reducing the effects of noise on ABR recordings.
The auditory steady state response (ASSR) is useful for estimating hearing threshold and relies on the ability of the auditory system to phase-lock and mimic the frequency and amplitude modulation of an external stimulus in the response. Although there is general agreement between thresholds obtained via auditory brainstem responses (ABR) and ASSR, discrepancies still exist. CE-Chirps have been successful at generating robust responses relative to tone-burst ABRs, and have been used in conjunction with ASSR in neonates and adults, albeit such applications of ASSR have not been extensively compared to thresholds obtained via ABR. The present study compares the narrow-band CE-Chirp evoked ASSR with click evoked ABR and behavioral methods of threshold estimation across 32 infants and toddlers. Results show that threshold estimation via CE-Chirp evoked ASSRs are highly correlated with those obtained via ABR and behavioral response audiometry for the frequencies of 0.5, 1, 2, and 4 kHz, including average responses across 2 and 4 kHz, and a combined average across all frequencies. This study suggests that narrow-band CE-Chirp ASSR, as is used in the Eclipse, accurately estimates behavioral response audiometry thresholds in infants and toddlers, even at 0.5 kHz. In addition, the use of narrow-band CE-Chirps may identify steeply sloping audiometric configurations that would be missed via click-evoked ABR.
This study evaluates the performance of the narrow-band CE-Chirp stimuli centred at 4 kHz and 1 kHz in a real-world clinical setting. The study was designed such that infants referred by the UK newborn hearing screen for ABR testing were first assessed using conventional tone burst stimuli at 4 kHz and 1 kHz, before repeating the procedure with the CE-Chirp stimuli. Key aspects of the performance were then compared i.e. response amplitude, Fmp (an objective indication of the likelihood of a response being present) and residual noise. The results from 42 infant ears showed that the mean ABR amplitudes to both 4 kHz and 1 kHz CE-Chirp stimuli, when compared to those from equivalent tone burst stimuli at the same level and comparable residual noises, were 64% greater. Fmp values for the CE-Chirp data were over twice as large as the corresponding tone burst data. Taken together these results indicate that CE-Chirp derived ABRs will offer significant time savings when testing infants, while the great Fmp values provide increased confidence in the presence of a response and this should translate into fewer “inconclusive” findings. Since the larger amplitude CE-Chirp responses will therefore lead to clear responses at lower levels than tone bursts, a more accurate estimation of the behavioural threshold is also proposed (i.e. an nHL-to-eHL correction factor that is 5 dB less for CE-Chirps than tone burst at 4 kHz and 1 kHz).
Auditory brainstem responses (ABR) are useful for evaluating the hearing status of infants that fail newborn hearing screenings or develop a postnatal hearing pathology. The quality of ABR recordings are largely dependent upon individual electroencephalogram (EEG) amplitude and state of arousal, and thus motivates obtaining ABR recordings under natural sleep, sedation or general anaesthesia. One way to reduce the contribution of high EEG levels upon the quality of ABR recordings is to obtain a more robust evoked response, which the CE-Chirp has shown promise. The present study analyzes the amplitude and amplitude growth function of CE-Chirp evoked ABRs retrospectively from 46 infants for comparison against the comparable literature data for adults and to click-evoked ABRs for infants. In addition, the effects of maturation on CE-chirp evoked ABR between 1 and 48 months of age is evaluated. Results show that CE-Chirp evoked ABR amplitudes for two groups of infants separated according to a criterion of 18 month of age are larger relative to responses reported in the literature for click-evoked ABRs from young infants. The CE-Chirp evoked ABRs are not substantially smaller for the older infants than those reported for adults; however, the CE-Chirp evoked ABR amplitudes are smaller for younger infants relative to their older infant and adult counterparts. The results suggest that use of the CE-Chirp evoked ABR improves the chance of overcoming the adverse effects of high EEG noise in ABR recordings and hence, stands to reduce recording time in young infants.
Rodrigues, GR., Ramos, N. and Lewis DR. (2013) International Journal of Pediatric Otorhinolaryngology, 77(9), pages 1555–1560.
A relatively recent innovation in auditory evoked potentials is the narrowband CE-chirp, a sound stimulus designed to improve synchrony of evoked neural activity. This paper describes the key characteristics of ABR amplitude and latency for CE-chirp stimuli over a range of frequencies and levels, in comparison to conventional tonepip stimuli in the same group of individuals.
Automated electrophysiological response detection is a key component of hearing screening programmes, and relies on balancing the time needed to complete the test, with appropriate statistical robustness in response detection. This article details a test strategy that may improve performance in ASSR detection by decreasing test time and increasing response detection rates.
This longitudinal study compares the accuracy of estimated hearing thresholds in hearing impaired infants using the ABR in the neonatal period, with the behavioural thresholds gathered at a later date when such behavioural testing became feasible. Agreement was around 10 dB for a 4 kHz tone-pip ABR and the corresponding behavioural threshold, and around 17 dB for the 1 kHz comparison.
This paper describes a research project which compares the ABRs in 11 normal-hearing young adults (N = 22 ears) in response to the Click, the CE-Chirp and the LS-Chirp (ref. 17) at a broad range of stimulus levels. The stimuli are delivered by two different insert earphones, the ER-3A and the ER-2. The ER-3A has an amplitude response that rolls of at about 4 kHz, whereas the ER-2 has an amplitude response which is flat all the way up to and beyond 10 kHz. The recordings are obtained with the Eclipse using a 30 nV background noise stop criteria and weighted averaging. For both chirps it is found that the ABRs at lower levels (i.e. below 60 dB nHL) are significantly larger with the ER-2 than with the ER-3A earphone, and further it is demonstrated that this finding most likely is due to the large differences between the amplitude-frequency responses of the two earphones.
This paper describes a reference study in which the behavioural thresholds to chirp stimuli are measured in a large group of normal-hearing individuals. The test group consists of 25 young adults (N = 50 ears) and the measurements are in compliance with the recommendations given in the ISO 389-9 standard. The test signals are the CE-Chirp and the four octave-band chirps, which are presented at two repetition rates, 20 and 90 stimuli/s, and using the ER-3A insert earphone. The calibration values are reported in dB p.e. SPL in the occluded-ear simulator. The results are similar to those from another investigation (PTB-study) and the values from the two, independent studies are therefore relevant for a future extension of the existing ISO 389-6 standard, which presently provides reference calibration values for standardized click and tone-burst stimuli delivered from various earphones.
This paper describes an experimental verification of the proposed level-specific model (ref. 17). The study compares the CE-Chirp with the LS-Chirp (and the standard Click) by recording the ABR from both ears in 10 normal-hearing, young adults (N = 20 ears). Both chirps have an electrical amplitude spectrum which is flat from 350 to 11.300 Hz (the IA CE-Chirp). The ER-3A earphone is used and the recordings are obtained with the Eclipse using a 30 nV background noise stop criteria and weighted averaging. The ABR amplitude, latency, and waveform are evaluated. The results clearly demonstrate the advantage of the LS-Chirp over the CE-Chirp at levels above 60 dB nHL.
This paper describes the development of a quantitative auditory model based on a ‘humanized’ nonlinear auditory-nerve model of Zilany and Bruce (2007). The model is able to account for the change in tone-burst evoked ABR latency with frequency, but underestimate changes in both click and tone-burst latency values with stimulus level. However, the model correctly predicts the non-linear ABR amplitude behaviour in response to different chirp stimuli (ref. 15, 16 & 17) and thus supports the hypothesis thatthe ABR generation strongly is influenced by the non-linear and dispersive processes in the cochlea.
This paper describes how the ABR amplitude is dependent of Chirp duration (sweeping rate) and stimulus level. A standard Click and five Chirps of different durations are presented at three levels of stimulation (20, 40 and 60 dB nHL) in 20 normal hearing adult ears. It is found that all the Chirps (except the longest one at 60 dB nHL) always produce larger ABR amplitudes than the Click. It is also found that the shorter Chirps are most efficient at higher levels whereas the longer Chirps are most efficient at lower levels. The paper concludes that two mechanisms appear to be involved: (1) upward-spread-of excitation at higher levels, and (2) an increased change of the cochlear-neural delay with frequency at lower levels. The observed changes in ABR amplitude and latency from the different chirp stimuli are consistent with this conclusion.
This paper describes a similar experiment as the one above. However, relative to Elberling et al (2010), recordings are obtained from 50 normal-hearing adults, the five Chirps have slightly different durations, the stimulus levels are lifted to 30 and 50 dB nHL, the frequency bandwidth of the stimuli is limited to 8 kHz, and some of the recording characteristics (e.g. HP-filter cut-off) have other values. Despite these differences the main experimental findings are the same as in ref. 15, but the effect of chirp duration on ABR amplitude is not as prominent as seen in ABR responses to different chirp stimuli at three levels of stimulation. The main reason for this result is probably the limited range of stimulus levels that has been used in this study.
This paper describes a novel approach to find the delay for each frequency component in order to design a family of chirps that optimally synchronizes all response components from across the cochlea (or brainstem) at all levels of stimulation. ABR latencies in response to octave-band chirp stimuli are collected from 48 normal-hearing adults and are used to formulate a latency-frequency model as a function of stimulus level. The delay compensations of the proposed model are similar to those found in the experimental studies described by Elderling et al (2010a) and Cebulla et al (2010).
Masking the non-test ear is necessary for certain audiometric configurations to ensure that the ABR recording accurately reflects the response (or lack of) of the test ear. However, data is limited in regards to the required level of masking noise necessary in ABR tests. This study attempts to quantify the relative masking level (RLM) in 22 normal-hearing adults for clicks and tone pips common to ABR tests via TDH-39 headphones and insert earphones. Results show that RLM is 4.5 dB greater when the noise level is increased from below the stimulus relative to when the noise is decreased from above the stimulus. Overall, RLMs are as much as 30 dB SPL at 500 Hz and 25 dB SPL across the frequencies of 1000, 2000 and 4000 Hz. RLMs approach 27 dB SPL for clicks. Therefore, a value of 30 dB above the stimulus is recommended for ensuring effective masking of the ABR stimulus in the same ear. The authors value is recommended when calculating the level of noise necessary to prevent cross-hearing during ABR testing and this is used in the NHSP masking calculator.
This paper describes how the Stacked ABR - at the output of the cochlea - attempts to compensate for the temporal dispersion of neural activation caused by the cochlear traveling wave in response to click stimulation. Compensation can also be made - at the input of the cochlea - by using a chirp stimulus. Previously it has been demonstrated that the Stacked ABR is sensitive to small tumors that are often missed by standard ABR latency measures. Because a chirp stimulus requires only a single data acquisition run, whereas the Stacked ABR requires six, the evidence justifying the use of a chirp for small tumor detection is evaluated. The sensitivity and specificity are compared of different Stacked ABRs formed by aligning the derived-band ABRs according to (1) the individual’s peak latencies, (2) the group mean latencies, and (3) the modelled latencies used to develop the chirp. Results suggest that for tumor detection with a chosen sensitivity of 95%, a relatively high specificity of 85% may be achieved with a chirp. Thus, it appears worthwhile to explore the actual use of a chirp because significantly shorter test and analysis times might be possible.
Simultaneous multiple stimulation of the ASSR.
Elberling, C., Cebulla, M., & Stürzebecher, E. (2008). In T. Dau, J. M. Buchholz, J. M. Harte, T. U. Christensen (Eds.), Auditory signal processing in hearing impaired listeners: 1st international symposium on auditory and audiological research (pp. 201-209). Centertryk A/S, Denmark: ISSAR 2007.
This paper describes some characteristics of the ASSR related to the use of multiple, simultaneous, band-limited chirp-stimuli. In a diagnostic study four one-octave-band chirp-stimuli (500, 1000, 2000 and 4000 Hz) were used to measure the ASSR-threshold in normal-hearing adults (N=20 ears). The four stimuli were presented simultaneously to both ears (eight stimuli) with rates at around 90/s. The ASSRs were detected automatically (error rate 5%), and the thresholds evaluated with a resolution of 5 dB. The ASSR thresholds were compared to the audiometric pure-tone thresholds and the deviations evaluated by the group means and standard deviations. These data compare favorably well with similar data reported by others. In a screening study a low-frequency chirp, (Lo: 180 – 1500 Hz) and a high-frequency chirp (Hi: 1500 –8000 Hz), is used to record the ASSR in newborns (N = 72). The two stimuli are presented both sequentially and simultaneously using a rate at about 90/s and a level of 35 dB nHL. The ASSRs are detected automatically (error rate 0.1%), and stimulus efficiency is evaluated by the detection time. The results from both studies demonstrate that simultaneous application of multiple, frequency-specific stimuli can effectively be applied without sacrificing response detection accuracy. However, in the screening study stimulus interactions are observed.
This paper describes how the temporal dispersion in the human cochlea can be compensated for by using a chirp designed from estimates of the cochlear delay based on derived-band auditory brainstem response (ABR) latencies. To evaluate inter-subject variability and level effects of such delay estimates, a large dataset is analyzed from (N = 81) normal-hearing adults (fixed click level) and from a subset thereof (different click levels). At a fixed click level, the latency difference between 5700 and 710 Hz ranges from about 2.0 to 5.0 ms, but over a range of 60 dB, the mean relative delay is almost constant. Modelling experiments demonstrate that the derived-band latencies depend on the cochlear filter build up time and on the unit response waveform. Because these quantities are partly unknown, the relationship between the derived-band latencies and the basilar membrane group delay cannot be specified. A chirp based on the above delay estimates is used to record ABRs in 10 normal-hearing adults (20 ears). For levels below 60 dB nHL, the gain in amplitude of chirp-ABRs to click-ABRs approaches two, and the effectiveness of chirp-ABRs compares favourably to Stacked-ABRs obtained under similar conditions.
This paper describes how a click stimulus sets up a traveling wave along the basilar membrane, which excites each of the frequency bands in the cochlea, one after another. Due to the lack in synchronization of the excitations, the compound response amplitude is low. A repetitive click-like stimulus can be set up in the frequency domain by adding a high number of cosines, the frequency intervals of which comply with the desired stimulus repetition rate. Straight-forward compensation of the cochlear traveling wave delay is possible with a stimulus of this type. As a result, better synchronization of the neural excitation can be obtained so that higher response amplitudes can be expected. The additional introduction of a frequency offset enables the use of a q-sample test for response detection. The results of investigations carried out on a large group of normal-hearing test subjects (N = 70) have confirmed the higher efficiency of this stimulus design. The new stimuli lead to significantly higher response SNRs and thus higher detection rates and shorter detection times. Using band-limited stimuli designed in the same manner, a "frequency-specific" hearing screening seems to be possible.
This paper describes how chirp stimuli can be used to compensate for the cochlear traveling wave delay in recordings of the ASSR (rate: ~90/s). The temporal dispersion in the cochlea is given by the traveling time, which in this study is estimated from latency-frequency functions obtained from (1) a cochlear model, (2) tone-burst auditory brain stem response ABR-latencies, and (3) derived-band ABR-latencies. These latency-frequency functions are assumed to reflect the group delay of a linear system that modifies the phase spectrum of the applied stimulus. On the basis of this assumption, three chirps are constructed and evaluated in normal-hearing subjects (N = 49). The ASSR to these chirps and to a click stimulus are compared at two levels of stimulation viz. 30 and 50 dB nHL and at a rate of 90/s. The chirps give shorter detection time and higher signal-to-noise ratio than the click. The shorter detection time obtained by the chirps is equivalent to an increase in stimulus level of 20 dB or more. The chirp based on the derived-band ABR-latencies appears to be the most efficient of the three chirps tested here. Overall, the results indicate that a chirp is a more efficient stimulus than a click for the recording of the ASSR in normal-hearing adults using transient sounds at a high rate of stimulation.
This paper describes how the ASSR is expected to be useful for the objective, frequency-specific assessment of hearing thresholds in small children. To detect ASSR close to the hearing threshold, a powerful statistical test in the frequency domain has to be applied. Hitherto so-called one-sample tests are used, which only evaluate the phase, or the phase and amplitude, of the first harmonic frequency (the fundamental). It is shown that higher harmonics with significant amplitudes are also contained in the ASSR spectrum. For this reason, statistical tests that only consider the first harmonic ignore a significant portion of the available information. The use of a q-sample test, which, in addition to the fundamental frequency, also includes higher harmonics in the detection algorithm leads to a better detection performance in normal-hearing and hearing impaired subjects (N = 57). The evaluation of test performance uses both detection rate and detection time.
This paper describes the use of the ASSR as a promising tool for the objective frequency-specific assessment of hearing thresholds in children. The stimulus generally used for ASSR recording (single amplitude-modulated carrier) only activates a small area on the basilar membrane. Therefore, the response amplitude is low. A stimulus with a broader frequency spectrum can be composed by adding several cosines whose frequency intervals comply with the desired stimulus repetition rate. Compensation for the traveling wave delay is also possible with a stimulus of this type, leading to a better synchronization of the neural response and consequently higher response amplitudes especially for low-frequency stimuli. The additional introduction of frequency offset, which minimizes the risks of detecting stimulus artefacts, enables the use of a q-sample test for the response detection, which is important particularly at the lowest frequencies. The results of investigations carried out on a large group of normal-hearing test subjects (N = 70) confirm the efficiency of this stimulus design. The new stimuli lead to significantly improved ASSRs with higher SNRs and thus higher detection rates and shorter detection times.
This paper describes how sequential statistical testing, which usually is applied in an automated response detection algorithm, is time efficient but unfortunately also increases the probability of a false rejection of the null-hypothesis. Therefore, in such test situations the test criterion is normally modified by means of the Bonferroni correction. However, when dealing with dependent or partly dependent data the Bonferroni correction will lead to an over-correction and will therefore not be optimal. A new method to find the optimal test criterion is devised and tested by means of Monte Carlo simulations using real background noise data acquired from clinical ASSR-recordings.
This paper describes an objective quantitative approach to the decision of when to stop averaging in the recording of ABRs. This decision is based on (1) the knowledge of the amplitude distributions of wave V in the ABRs of normal-hearing individuals for varying stimulus levels, (2) calculated estimates of the residual background noise in the average, and (3) the use of a quantitative statistical response detector. Several reasons for terminating an averaging process are presented along with a specific protocol for each of the reasons. These protocols provide a general but consistent framework to address the issue of when to stop averaging and will thus improve the efficiency of clinical ABR testing. Furthermore, it is quite possible to automate the procedure and the decision process.
This paper describes the nature of the residual background noise in ABR averages in normal-hearing subjects. The residual noise is estimated with the Fsp technique. Low-level click stimuli are presented in 2-dB steps in the range from 30 to 48 dB p.e.SPL (approximately from -2 to +16 dB nHL) and for each stimulus level, 10 000 sweeps are acquired and stored for subsequent analysis. The shortcomings of artifact rejection and traditional averaging are demonstrated. It is further demonstrated how weighted averaging can help minimize these shortcomings. Finally, it is analyzed how the number of sweeps per block influences the ability of weighted averaging to control the destructive effects of non-stationary background noise. It turns out that reducing block size from 256 to 32 sweeps per block improves the weighted averaging significantly - but with a small amount only. Minimizing the destructive effects increases the value of statistical techniques used for objective ABR detection or to control the quality of ABR recordings. It is concluded that these techniques in combination improve not only the accuracy of test interpretation but also the efficiency of clinical test time, which is becoming important for the control of medical costs.
This paper describes and analyzes ABRs recorded from ten normal-hearing subjects in response to 100 μs clicks from a TDH 49 earphone at a rate of 48 pps and at levels randomly varied in 2-dB steps between 34 and 52 dB p.e.SPL (approximately 0 - 20 dB nHL). At each level, 10 000 sweeps are averaged using weighted averaging. A running estimate of the signal-to-noise ratio (SNR), FSP, is used to detect the presences of the ABR. The median threshold is found at 38 dB p.e.SPL (approximately 5 dB nHL). The mean averaged background noise level is 11.3 nVrms, and the "true" ABR amplitude function crosses this value at 35.5 dB p.e.SPL (2 – 3 dB nHL), which indicates the level where the SNR = 1. By extrapolation it is found that the ABR amplitude becomes zero at 32 dB p.e.SPL. The perceptual thresholds of the click are estimated by means of a modified block up-down procedure and the median value is found at 33 dB p.e.SPL. The slope of the amplitude function and the magnitude of the averaged background noise are the two factors responsible for the ABR threshold sensitivity which thus depends on both physiological and technical parameters. Therefore, these have to be considered together with the method of detection when the ABR is used as an indicator of the hearing sensitivity.
This paper describes a method to recover the ABR by weighted averaging. The method is an effective technique to deal with the destructive effect of fluctuating, non-stationary background noise, and is based on a statistical approach called ‘Bayesian inference’. The contribution of the individual sweep (or block of sweeps) is weighted inversely proportional to the level of background noise during the acquisition of the sweep. Based on 50 sets of clinical recordings the weighted averaging method is evaluated. Weighted averaging is always as good as or better than traditional averaging, and in about 30% of the cases the weighted averaging improves the recovered ABR significantly over what is obtained by traditional averaging. In these cases the traditional averaging would require 50% more sweeps to be averaged in order to obtain the same precision of the ABR, and the variance of the wave V latency is improved by a factor of approximately two.
This paper describes our early attempt to estimate the signal-to noise ratio of the averaged ABR. In the clinic, ABRs are recovered from the on-going background noise by averaging a number of sweeps. Normally, a test protocol will prescribe a fixed number of sweeps to be averaged and will recommend replications to be obtained. However, since both the ABR and the background noise differ across individual subjects both in magnitude and in other characteristics, such a test protocol can never ensure a given minimum ‘quality’ or signal-to-noise (response-to-noise) ratio, SNR, of the final recovered ABR. Therefore a statistical method is developed in order to estimate the SNR of the recorded ABR during the on-going averaging process. The method calculates the FSP, which is the squared ratio of the estimated magnitude of the ABR to that of the averaged background noise. The method can be employed on-line as an adaptive strategy (1) to estimate the number of sweeps necessary to obtain a given minimum SNR (quality) of the ABR recorded at supra threshold levels, or (2) to automatically detect the presence of an ABR near threshold.
Otoacoustic emissions (OAEs) are responses of the outer hair cells within the cochlea that indicate normal peripheral function of the auditory system. OAE detection is dependent upon the integrity of the ear canal, middle-ear, ossicular chain and cochlea. Any disruption along this path may preclude the detection of OAEs. One such disruption includes the presence of deviant middle-ear pressure. This article reviews some of the literature indicating that compensation for deviant middle-ear pressure improves OAE detection. The authors also present a case that shows pressurizing the ear canal to the pressure of the peak compliance of the middle ear (-167 daPa) via a Titan instrument increases the DPOAE response by ~5 to 10 dB below 2 kHz relative to non-compensated DPOAEs. This suggests that accounting for deviant middle-ear pressure via the Titan OAE module improves detection of OAEs when negative middle ear pressure is present.
Distortion product otoacoustic emissions (DPOAEs) are an objective method for evaluating the integrity of the cochlea; however, middle-ear dysfunction can attenuate the DPOAE response including cases where peak middle-ear pressure deviates from ambient pressure. The effect of deviant middle-ear pressure mostly affects the DPOAE response at frequencies below 1 to 2 kHz. Amongst 12 ototogically normal young adults, the objective of this study was twofold: 1) to quantify the change in DPOAE level across a range (-200 to +200 daPa) of static pressures applied in the ear canal, and 2) to determine the slope of level change across this range in 50 daPa steps. Generally, DPOAEs were largest at 0 daPa for all frequencies of 1, 2, 3 and 4 kHz, and the overall mean DPOAE level reduced by 2.3 dB for each 50 daPa deviation away from ambient pressure. This suggests that accounting for positive or negative pressure in the middle-ear may facilitate the evaluation of cochlear integrity via OAEs in cases that would otherwise preclude OAE detection. The Titan has the ability to measure DPOAEs while also accounting for the presence of deviant middle-ear pressure.
Otoacoustic emissions (OAEs) describe soft sounds measured in the ear canal that originate in the cochlea via transmission through the middle ear. The presence of OAEs indicate normally functioning outer hair cells within the inner ear. However, OAE detection also depends upon the integrity of conductive path via the middle ear. Therefore, a middle ear pathology may preclude OAE detection, even though outer hair cell function is normal. Such middle ear involvement may include the presence of middle-ear pressure that deviates from the ambient pressure in the ear canal, e.g., negative middle ear pressure, which has been shown to attenuate OAEs in the low frequencies. Matching the pressure in the sealed ear canal to the deviant pressure in the middle ear cavity may improve OAE detection assuming that the outer hair cell function is normal. The current study describes the effect of compensating for deviant middle-ear pressure on the amplitude and phase of transient-evoked OAEs (TEOAEs) in 59 children with near-normal and more severe deviant tympanic peak pressure. Subsequent to normalizing abnormal middle ear pressure in pathologic ears, results indicate that the OAEs increase in amplitude and phase lag, and hence, improve detectability. Specifically, ears with mild negative middle ear pressure between -120 and -40 daPa show an average increase of 8 dB near 1 kHz, no level change above 1.5 kHz and a phase increase by 0.4 pi near 1.5 kHz; ears with moderate negative pressure between -200 and -120 daPa show an increase up to 11 dB near 1 kHz and extending up to 2 kHz, and a phase increase by 0.5 pi up to 5 kHz; and finally, ears with the largest negative pressure between -280 and -200 daPa do not show an increase in amplitude but do show a slight increase in phase for the frequencies above 2 kHz over the moderate group. Comparisons made to a Zwislocki middle ear model suggest that the effect of compensating for negative middle ear pressure is a function of a decrease in the stiffness of the middle ear structures. This result supports the notion that compensating for negative middle ear pressure in the measurement of OAEs, as is possible in the Titan TEOAE module, increases the robustness of OAE detection.
Distortion product otoacoustic emissions (DPOAEs) and transient-evoked OAEs (TEOAEs) assist in the evaluation of cochlear function. Negative middle-ear pressure is the most common dysfunction of the middle ear, which can result in hearing loss by diminishing the efficiency of energy transmission via the middle ear cavity. Because OAEs rely on transmission via the middle ear, OAE detection is diminished in the presence of deviant pressure in the ear canal or middle ear. The present study measured DPOAE levels in normal human ears upon voluntarily produced negative middle-ear pressure, and negative and positive ear canal pressures. The author's goal is to compare how negative middle-ear pressure, positive ear-canal pressure, and negative ear-canal pressure, all of the same magnitude, each affect the DPOAE response. Results indicate that positive ear-canal pressure and negative middle-pressure within each of the seven categorical ranges of pressure (e.g., -70 to -95 daPa) produce very similar effects on DPOAE amplitude, which is distinct from the effects of negative ear-canal pressure on the DPOAE amplitude. Specifically, positive ear-canal pressure and negative middle-ear pressure reduce DPOAE level at f2 frequencies from 600 to 1500 Hz, and at 3000 Hz; and increase DPOAE amplitude at 8000 Hz. The effects of applying negative ear-canal pressure have a relatively lesser effect. This suggests that compensating for the presence of middle-ear pressure has the benefit of increasing the ability to detect a DPOAE for frequencies below 2000 Hz and for 3000 Hz.
Evoked otoacoustic emissions (OAE) refer to the acoustic energy recorded in the ear canal generated from the cochlea in response to an evoking stimulus. The evoking stimulus is typically a transient signal or a pair of tones, which produce transient OAEs (TEOAEs) or distortion-product OAEs (DPOAEs), respectively. OAE generation indicates function of the outer hair cells within the cochlea. In addition to the health of cochlear hair cells, the measurement of OAEs depends upon the forward transmission of the evoking acoustic energy from ear canal to the cochlea, and reverse transmission of the cochlear response from the cochlea back to the ear canal. Because the middle-ear is positioned between the ear canal and the cochlea, any dysfunction within the middle ear cavity can alter the OAE. One such common example is negative middle-ear pressure caused by Eustachian tube dysfunction. The objective of this study is to examine the effect of middle-ear pressure on DPOAEs and to validate the effect of compensating for negative middle-ear pressure on DPOAEs. Within a sample of 36 adults with no hearing loss or otologic disease, negative-middle ear pressure reduces DPOAEs for an f2 of 1000 Hz and below. Specifically, negative-middle between -40 and -65 daPa reduces DPOAEs by 4-6 dB, and further reduces DPOAEs down to -12 dB as middle-ear pressure decreases down to -420 daPa. Further, the f2 frequency of 3000 Hz shows a similar reduction in DPOAEs as the magnitude of negative pressure is increased. DPOAEs do not show a significant change for f2 frequencies of 2000, 4000, and 6000 Hz. However, DPOAEs tend to increase for f2 frequencies of 8000 Hz for negative middle ear pressure below -160 daPa, albeit the change is not significant. When pressure applied to the ear canal matches the pressure at peak compliance of the middle ear, the DPOAE response is corrected and resembles the DPOAE response with no negative middle-ear pressure. Finally, the peak and notch of the DPOAE response increases as negative middle-ear pressure decreases, which suggests a change in the resonant attributes of the middle-ear cavity. This study suggests that compensation for deviant middle-ear pressure improves the level of the DPOAE.
IMPEDANCE / Wide Band Tympanometry
Consensus Statement: Eriksholm Workshop on Wideband Absorbance Measures of the Middle Ear.
Feeney MP, Hunter LL, Kei J, Lilly DJ, Margolis RH, Nakajima HH, Neeley ST, Prieve BA, Rosowski JJ, Sanford CA, Schairer KS, Shahnaz N, Stenfelt S, Voss SE. (2013)
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This collection of articles summarizes the efficient and effective diagnosis of the ‘dizzy’ patient by providing a step-by-step guide to the core components of a typical audio-vestibular assessment.
This collection of articles summarizes the efficient and effective diagnosis of the ‘dizzy’ patient by providing a step-by-step guide to the core components of a typical audio-vestibular assessment.
This collection of articles summarizes the efficient and effective diagnosis of the ‘dizzy’ patient by providing a step-by-step guide to the core components of a typical audio-vestibular assessment.