Otoacoustic emissions evoked by 0.5 kHz tone bursts

Visual attention does not affect the reliability of otoacoustic emission or medial olivocochlear reflex

This study investigated whether visual attention affects the reliability (i.e., repeatability) of transiently evoked otoacoustic emission (TEOAE) magnitudes or of medial olivocochlear reflex (MOCR) estimates. TEOAEs were measured during three visual attentional conditions: control (subject were seated with eyes closed); passive (subjects looked at a pattern of squares on a computer screen); and active (subjects silently counted an occasionally inverted pattern). To estimate reliability, the whole recording session was repeated the next day. The results showed that visual attention does not significantly affect TEOAE or MOCR magnitudes-or their reliability. It is therefore possible to employ visual stimuli (e.g., watching a silent movie) during TEOAE experiments, a procedure sometimes used during testing to prevent subjects from falling asleep or to keep children still and quiet.

Otoacoustic emissions from ears with spontaneous activity behave differently to those without: Stronger responses to tone bursts as well as to clicks

It has been reported that both click-evoked otoacoustic emissions (CEOAEs) and distortion product otoacoustic emissions (DPOAEs) have higher amplitudes in ears that possess spontaneous otoacoustic emissions (SOAEs). The general aim of the present study was to investigate whether the presence of spontaneous activity in the cochlea affected tone-burst evoked otoacoustic emissions (TBOAEs). As a benchmark, the study also measured growth functions of CEOAEs. Spontaneous activity in the cochlea was measured by the level of synchronized spontaneous otoacoustic emissions (SSOAEs), an emission evoked by a click but closely related to spontaneous otoacoustic emissions (SOAEs, which are detectable without any stimulus). Measurements were made on a group of 15 adults whose ears were categorized as either having recordable SSOAEs or no SSOAEs. In each ear, CEOAEs and TBOAEs were registered at frequencies of 0.5, 1, 2, and 4 kHz, and input/output functions were measured at 40, 50, 60, 70, and 80 dB SPL. Global and half-octave-band values of response level and latency were estimated. Our main finding was that in ears with spontaneous activity, TBOAEs had higher levels than in ears without. The difference was more apparent for global values, but were also seen with half-octave-band analysis. Input/output functions had similar growth rates for ears with and without SSOAEs. There were no significant differences in latencies between TBOAEs from ears with and without SSOAEs, although latencies tended to be longer for lower stimulus levels and lower stimulus frequencies. When TBOAE levels were compared to CEOAE levels, the latter showed greater differences between recordings from ears with and without SSOAEs. Although TBOAEs reflect activity from a more restricted cochlear region than CEOAEs, at all stimulus frequencies their behavior still depends on whether SSOAEs are present or not.

Novel neuro-audiological findings and further evidence for TWNK involvement in Perrault syndrome

BACKGROUND

Hearing loss and ovarian dysfunction are key features of Perrault syndrome (PRLTS) but the clinical and pathophysiological features of hearing impairment in PRLTS individuals have not been addressed. Mutations in one of five different genes HSD17B4, HARS2, LARS2, CLPP or TWNK (previous symbol C10orf2) cause the autosomal recessive disorder but they are found only in about half of the patients.

METHODS

We report on two siblings with a clinical picture resembling a severe, neurological type of PRLTS. For an exhaustive characterisation of the phenotype neuroimaging with volumetric measurements and objective measures of cochlear hair cell and auditory nerve function (otoacustic emissions and auditory brainstem responses) were used. Whole exome sequencing was applied to identify the genetic cause of the disorder. Co-segregation of the detected mutations with the phenotype was confirmed by Sanger sequencing. In silico analysis including 3D protein structure modelling was used to predict the deleterious effects of the detected variants on protein function.

RESULTS

We found two rare biallelic mutations in TWNK, encoding Twinkle, an essential mitochondrial helicase. Mutation c.1196A>G (p.Asn399Ser) recurred for the first time in a patient with PRLTS and the second mutation c.1802G>A (p.Arg601Gln) was novel for the disorder. In both patients neuroimaging studies showed diminished cervical enlargement of the spinal cord and for the first time in PRLTS partial atrophy of the vestibulocochlear nerves and decreased grey and increased white matter volumes of the cerebellum. Morphological changes in the auditory nerves, their desynchronized activity and partial cochlear dysfunction underlay the complex mechanism of hearing impairment in the patients.

CONCLUSIONS

Our study unveils novel features on the phenotypic landscape of PRLTS and provides further evidence that the newly identified for PRLTS TWNK gene is involved in its pathogenesis.

Otoacoustic emissions in newborns evoked by 0.5kHz tone bursts

BACKGROUND

Otoacoustic emissions (OAEs) are currently widely used in newborn hearing screening programs. OAEs evoked by transients (TEOAEs) in newborns are usually characterized by large response levels at higher frequencies but lower frequencies are affected by physiological noise. The purpose of the present study was to acquire responses at lower frequencies by measuring OAEs evoked by 0.5kHz tone bursts (TBOAEs).

METHODS

Otoacoustic emissions (OAEs) were recorded from 49 newborns. Measurements were made using the ILO 292 equipment from Otodynamics. In each ear, three measurements were made: first with a standard click stimulus at 80dB pSPL (CEOAEs), a second using a 0.5kHz tone burst at 80dB pSPL (TBOAEs), and a third recording of spontaneous OAEs (SOAEs). Global and half-octave-band values of OAE signal-to-noise ratio (SNR) and response level were used to assess statistical differences between CEOAEs and 0.5kHz TBOAEs. Additionally, time-frequency (TF) analysis of signals was performed using the matching pursuit method.

RESULTS

Global levels were highest for CEOAEs. However, at low frequencies (0.7-1kHz), 0.5kHz TBOAEs had significantly higher levels and SNRs than CEOAEs. At these frequencies, SNRs of CEOAEs were usually below 0dB. At 0.5kHz there were no statistically significant differences between CEOAEs and TBOAEs. In ears with recordable SOAEs, CEOAEs and TBOAEs had higher levels and SNRs than in ears without SOAEs.

CONCLUSIONS

Use of 0.5kHz TBOAEs may be a useful addition to standard CEOAE tests in newborns. They provide information about lower frequencies, a region where CEOAEs are usually prone to noise. The presence of SOAEs affects the magnitudes of both CEOAEs and TBOAEs.

Tone burst evoked otoacoustic emissions in different age-groups of schoolchildren

INTRODUCTION

Otoacoustic emissions (OAEs) are believed to be good predictors of hearing status, particularly in the 1-4kHz range. However both click evoked OAEs (CEOAEs) and distortion product OAEs (DPOAEs) perform poorly at 0.5kHz. The present study investigates OAEs in the lower frequency range of 0.5-1kHz evoked by 0.5kHz tone bursts (TBOAEs) in schoolchildren and compares them with emissions evoked by clicks.

METHODS

Measurements were performed for two groups of normally hearing schoolchildren. Children from 1st grade (age 6-7 years) and children from 6th grade (age 11-12 years). Tympanometry, pure tone audiometry, and OAE measurements of CEAOEs, 0.5kHz TBOAEs, and spontaneous OAEs (SOAEs) were performed. Additionally, analysis by the matching pursuit method was conducted on CEOAEs and TBOAEs to assess their time-frequency (TF) properties.

RESULTS

For all subjects OAEs response levels and signal to noise ratios (SNRs) were calculated. As expected, CEOAE magnitudes were greatest over the range 1-4kHz, with a substantial decrease below 1kHz. Responses from the 0.5kHz TBOAEs were complementary in that the main components occurred between 0.5 and 1.4kHz. In younger children, TBOAEs had SNRs 4-8dB smaller in the 0.5-1.4kHz range. In addition, CEOAEs had lower SNRs in the 0.7-1.4kHz range, by 3-5dB. TBOAEs in younger children had maximum SNRs shifted toward 1-1.4kHz, whereas in older children it was more clearly around 1kHz. The differences in response levels were less evident. The presence of SOAEs appreciably influenced both CEOAEs and TBOAEs, and TF properties of both OAEs did not differ significantly between grades.

CONCLUSION

TBOAEs evoked at 0.5kHz can provide additional information about frequencies below 1kHz, a range over which CEOAEs usually have very low amplitudes. The main difference between the two age groups was that in older children CEOAEs and 0.5kHz TBOAEs had higher SNRs at 0.5-1.4kHz. Additionally, for ears with SOAEs, 0.5kHz TBOAEs had higher response levels and SNRs similar to CEOAEs.

Low-frequency otoacoustic emissions in schoolchildren measured by two commercial devices

OBJECTIVE

Click evoked otoacoustic emissions in children are known to be good indicators of hearing function when used in the frequency range 1.5-4 kHz. Using two commercial devices, the present study investigates the usefulness of responses in the lower frequency range of 0.5-1 kHz evoked by 0.5 kHz tone bursts.

METHODS

Otoacoustic emissions (OAEs) were recorded from the ears of 37 schoolchildren (age 12-13 years). OAE measurements were then made using two devices: the ILO 292 (Otodynamics) and the HearId (Mimosa Acoustics). Each device was used for two measurements: first with a standard click stimulus at 80 dB pSPL (CEOAEs) and a second using a 0.5 kHz tone burst at 80 dB pSPL (TBOAEs). Pure tone audiometry and tympanometry were also conducted. Half-octave-band values of OAE signal to noise ratios (SNRs) and response levels were used to assess statistical differences.

RESULTS

Both devices provided similar SNR results for click and tone burst stimuli, although the ILO device generated slightly higher response levels for clicks. For the 0.5 kHz tone bursts, both devices evoked very weak responses at 0.5 kHz and the peak response occurred at 0.7-1 kHz. Generally, CEOAE SNRs were about 10 dB in the 1-4 kHz range, while SNRs for 0.5 kHz TBOAEs were about 10 dB at 0.7-1 kHz.

CONCLUSIONS

0.5 kHz TBOAEs could be measured in children as effectively as CEOAEs. They can provide additional information about the 0.7-1 kHz frequency range, a range over which CEOAEs do not usually contain responses above the noise floor. The main difficulty was that the maxima of the 0.5 kHz TBOAEs occurred at frequencies of 0.7-1 kHz, probably because of spectral splatter from the short tone burst stimulus and from rapidly falling responses of the cochlea and the recording system at low frequencies.

Chirp-evoked otoacoustic emissions in children

OBJECTIVE

The purpose of the study was to investigate the properties of otoacoustic emissions (OAEs) evoked by chirp stimuli and compare them with standard click-evoked OAEs. Differences between evoked OAEs in children with and without spontaneous otoacoustic emissions (SOAEs) were also assessed.

METHODS

OAEs were first recorded from 54 children (age 4-10 years) in a screening setup. In each ear five OAE measurements were made using two types of chirps (7.5 ms and 10.5 ms) at around 70 dB pSPL; clicks at 70 and 80 dB pSPL; and a standard synchronized SOAE stimulation protocol. Tympanometry was also conducted. Pass/refer criteria based on signal to noise ratios (SNRs) were applied to all OAEs. Pass/refer rates from all methods (OAEs evoked by chirps and clicks, and tympanometry) were compared. Additionally, half-octave-band values of OAE SNRs and response levels were used to assess statistical differences.

RESULTS

Chirp-evoked OAEs generated a similar number of passes to click-evoked OAEs when the same level of stimulus was used. When using lower stimulus levels, both chirp- and click-evoked OAEs diagnosed nearly all ears that failed tympanometry. The response levels and SNRs of OAEs evoked by clicks and chirps were very similar. The highest response levels were in the 1.4 kHz half-octave band. The SNRs for ears with SOAEs were highest at 1.4 kHz, whereas they were at 4 kHz for ears without SOAEs. Both response levels and SNRs were higher by about 5 dB for ears with SOAEs than ears without SOAEs. Also all ears with SOAEs generated a pass result in screening, while ears without SOAEs gave a pass less frequently (at least 30% fewer cases).

CONCLUSIONS

The results suggest that performance of chirp-evoked OAEs for screening purposes is similar to click-evoked OAEs when the same stimulus level is applied. OAEs evoked with lower stimulus levels (70 vs. 80 dB pSPL) are more sensitive to middle ear pathology. The presence of SOAEs significantly influences the pass rates of OAEs evoked by chirps and clicks.

Moments of click-evoked otoacoustic emissions in human ears: group delay and spread, instantaneous frequency and bandwidth

A click-evoked otoacoustic emission (CEOAE) has group delay and spread as first- and second-order temporal moments varying over frequency, and instantaneous frequency and bandwidth as first- and second-order spectral moments varying over time. Energy-smoothed moments were calculated from a CEOAE database over 0.5-15 kHz bandwidth and 0.25-20 ms duration. Group delay and instantaneous frequency were calculated without phase unwrapping using a coherence synchrony measure that accurately classified ears with hearing loss. CEOAE moment measurements were repeatable in individual ears. Group delays were similar for CEOAEs and stimulus-frequency OAEs. Group spread is a frequency-specific measure of temporal spread in an emission, related to spatial spread across tonotopic generation sites along the cochlea. In normal ears, group delay and spread increased with frequency and decreased with level. A direct measure of cochlear tuning above 4 kHz was analyzed using instantaneous frequency and bandwidth. Synchronized spontaneous OAEs were present in most ears below 4 kHz, and confounded interpretation of moments. In ears with sensorineural hearing loss, group delay and spread varied with audiometric classification and amount of hearing loss; group delay differed between older males and females. CEOAE moments reveal clinically relevant information on cochlear tuning in ears with normal and impaired hearing.

Otoacoustic emissions in neonates measured with different acquisition protocols

OBJECTIVE

The purpose of the study was to investigate the properties of neonatal transiently evoked otoacoustic emissions (TEOAEs) recorded with three most popular stimulation protocols. Differences between the recorded TEOAEs with and without spontaneous otoacoustic emissions (SOAEs), were also assessed. In addition two more issues were addressed: (i) the effect of windowing on the TEOAE responses; and (ii) the contribution of the TEOAE segment from 12.5 to 20 ms to the overall TEOAE response.

METHODS

TEOAEs and SOAEs were recorded from 50 normal hearing neonates using linear, non-linear, QuickScreen and standard synchronized SOAE stimulation protocols. Global and half-octave-band values of TEOAE reproducibility and response level were used to assess statistical differences in the recorded responses. Furthermore protocol differences were evaluated in different recording windows from 2.5 to 12.5 and 12 to 20 ms.

RESULTS

Data from the linear protocol presented TEOAE parameters with the highest values. The differences between recordings with longer and shorter acquisition windows were especially apparent in 1-1.4 kHz frequency range. Furthermore the data have shown that the low frequency TEOAE components are a significant part of the TEOAE response, especially in ears without SOAEs.

CONCLUSIONS

The results suggest that TEOAE protocols using short recording windows (i.e. QuickScreen) can be used only for a fast detection of a valid TEOAE. For more sophisticated clinical analyses the standard 20 ms TEOAE recording window is more appropriate. The presence of SOAEs significantly influences TEOAEs. Ears with SOAEs presented higher values of TEOAE parameters especially in the 2-4 kHz range. On the other hand, in the ears without SOAEs low frequency components contribute more to the signal.

Time-frequency analysis of linear and nonlinear otoacoustic emissions and removal of a short-latency stimulus artifact

Click-evoked otoacoustic emissions (CEOAEs) are commonly recorded as average responses to a repetitive click stimulus. If the click train has constant polarity, a linear average results; if it contains a sequence of clicks of differing polarity and amplitude, a nonlinear average can be calculated. The purpose of this study was to record both protocols from the same set of ears and characterize the differences between them. The major features of CEOAEs were similar under both protocols with the exception of a region spanning 0-5 ms in time and 0-2.2 kHz in frequency. It was assumed that the signal derived from the linear protocol was contaminated by stimulus artifact, and so a simple procedure was used--involving high-pass filtering and time-windowing--to remove components of this artifact. This procedure preserved the short-latency, high-frequency responses; it also produced a marked similarity in the time-frequency plots of recordings made under the two protocols. This result means it is possible to take advantage of the better signal-to-noise ratio of the linear data compared to its nonlinear counterpart. Additionally, it was shown that CEOAEs recorded under the linear protocol appear to be less dependent on the presence of spontaneous otoacoustic emissions (SOAEs).

Detecting high-frequency hearing loss with click-evoked otoacoustic emissions

In contrast to clinical click-evoked otoacoustic emission (CEOAE) tests that are inaccurate above 4-5 kHz, a research procedure measured CEOAEs up to 16 kHz in 446 ears and predicted the presence/absence of a sensorineural hearing loss. The behavioral threshold test that served as a reference to evaluate CEOAE test accuracy used a yes-no task in a maximum-likelihood adaptive procedure. This test was highly efficient between 0.5 and 12.7 kHz: Thresholds measured in 2 min per frequency had a median standard deviation (SD) of 1.2-1.5 dB across subjects. CEOAE test performance was assessed by the area under the receiver operating characteristic curve (AUC). The mean AUC from 1 to 10 kHz was 0.90 (SD=0.016). AUC decreased to 0.86 at 12.7 kHz and to 0.7 at 0.5 and 16 kHz, possibly due in part to insufficient stimulus levels. Between 1 and 12.7 kHz, the medians of the magnitude difference in CEOAEs and in behavioral thresholds were <4 dB. The improved CEOAE test performance above 4-5 kHz was due to retaining the portion of the CEOAE response with latencies as short as 0.3 ms. Results have potential clinical significance in predicting hearing status from at least 1 to 10 kHz using a single CEOAE response.

Use of the matching pursuit algorithm with a dictionary of asymmetric waveforms in the analysis of transient evoked otoacoustic emissions

Transiently evoked otoacoustic emissions (TEOAEs) are normally modeled as the sum of asymmetric waveforms. However, some previous studies of TEOAEs used time-frequency (TF) methods to decompose the signals into symmetric waveforms. This approach was justified mainly as a means to reduce the complexity of the calculations. The present study extended the dictionary of numeric functions to incorporate asymmetric waveforms into the analysis. The necessary calculations were carried out using an adaptive approximation algorithm based on the matching pursuit (MP) numerical technique. The classic MP dictionary uses Gabor functions and consists of waveforms described by five parameters, namely, frequency, latency, time span, amplitude, and phase. In the present investigation, a sixth parameter, the degree of asymmetry, was added in order to enhance the flexibility of this approach. The effects of expanding the available functions were evaluated by means of both simulations using synthetic signals and authentic TEOAEs. The resulting analyses showed that the contributions of asymmetric components in the OAE signal are appreciable. In short, the expanded analysis method brought about important improvements in identifying TEOAE components including the correct detection of components with long decays, which are often related to spontaneous OAE activity, the elimination of a "dark energy" effect in TF distributions, and more reliable estimates of latency-frequency relationships. The latter feature is especially important for correct estimation of latency-frequency data, which is a crucial factor in investigations of OAE-generation mechanisms.