Otoacoustic emissions

TEOAE amplitude growth, detectability, and response threshold in linear and nonlinear mode and in different time windows

Transitory evoked otoacoustic emissions (TEOAE) have been recorded in 60 ears of 31 adult volunteers with nearly normal hearing at stimulus levels ranging from 83 dB SPL peak equivalent down to the individual response threshold using linear and nonlinear recording mode. The stimulus level dependence of response incidence and amplitude has been analysed for the integral response and in time windows selecting response components of limited latency ranges. At stimulus levels above 70 dB SPL peak equivalent the TEOAE records received in linear mode are contaminated with stimulus artifacts. At moderate stimulus levels the TEOAE amplitude differs only to a small extent between the two recording modes. At low levels the linear mode turns out to be better suited for signal detection due to its inherent lower noise level. The response threshold, defined as the highest stimulus level yielding a reproducibility of at least 60%, is significantly correlated to hearing threshold. The consideration of time windowed responses yields best results with respect to incidence and threshold of responses in the latency range between 5 and 10 ms, but it does not enhance frequency specificity.

Hypoacousis prevalence in Kaiowá and Guarani indigenous children

OBJECTIVES: to determine hypoacousis prevalence in Kaiowá and Guarani indigenous children. METHODS: a cross-sectional study was performed using a sample of 126 indigenous children from zero to 59 months old from the Caarapó Indian Reserve, Mato Grosse do Sul, Brazil. Hearing ability screening was performed by measuring transient evoked otoacoustic emissions. Children with hearing impairment were retested. Confirmed cases following retest were referred to imitanciometry testing. RESULTS: during hearing ability screening, 25 (23.6%) children showed hearing impairment. Seventeen children had normal outcomes during retest and six of them confirmed hearing impairment and were referred to imitanciometry testing. Hypoacousis prevalence identified by the study reached 5.6%, 3 (2.8%) and 3 (2.8%) suggestive of conductive and sensorineural types, respectively. The last ones were referred to complementary otorhinolaryngologic assessment for diagnosis confirmation. Hearing impairment cases determined by this study were not statistically significant when related to gender and age. CONCLUSIONS: problems concerning the prevalence of hearing impairment determined in the focused population suggest the need for hearing health programs to be developed with other child health programs.

Temporal nonlinearity revealed by transient evoked otoacoustic emissions recorded to trains of multiple clicks

A series of detailed experiments is described that investigates how a transient evoked otoacoustic emission (TEOAE) recorded to one-click stimulus is affected by the presence of a variable number of preceding clicks presented over a range of interclick intervals (ICIs). Part of the rationale was to determine if the resulting nonlinear temporal interactions could help explain the amplitude reduction seen when TEOAEs are recorded at very high click rates, as when using maximum length sequence stimulation. Amongst the findings was that the presence of a preceding train of clicks could either suppress or enhance emission amplitude, depending on the number of clicks in the train and the ICI. Results also indicated that the duration of the click trains, rather than the ICI, was the important factor in yielding the most suppressed response and that this seemed to depend on stimulus level. The results recorded at two levels also suggested that the cochlear temporal nonlinearity being monitored was in part related to the nonlinear process that determines the compressive input/output function for stimulus level. It is hypothesised that nonlinear temporal overlap of vibration patterns on the basilar membrane may underlie much of the pattern of results.

Comparison of transient evoked otoacoustic emission thresholds recorded conventionally and using maximum length sequences

Presenting clicks according to maximum length sequences (MLSs) enables transient evoked otoacoustic emissions (TEOAEs) to be recorded at very high stimulation rates. Despite a decrease in TEOAE amplitude, the very large number of responses obtainable at high rates means that both signal to noise ratio (SNR) and detection sensitivity increase as the click rate increases. This study characterises conventional and MLS TEOAEs near threshold for a group of normally hearing adults. Stimulus presentation rates of 40 clicks/s (conventional) and 5000 clicks/s (MLS) were used. Compared to conventional recordings, the MLS technique enabled smaller responses to be detected, when averaged for the same time and to the same SNR. TEOAE amplitude recorded at detection threshold for MLS responses was 13 dB lower than that recorded conventionally. For each individual, MLS recording also produced clear, repeatable responses at stimulus levels below the detection threshold for conventional TEOAEs. The click level at TEOAE threshold was 12 dB lower for MLS compared to conventional emissions. These results suggest that TEOAE thresholds are not absolute but strongly related to the detection sensitivity of the recording system and physiological noise. The initial growth rates and the shape of input/output functions were found to be similar for the two recording techniques.

Suppression of distortion product otoacoustic emissions and hearing threshold

A distortion product otoacoustic emission (DPOAE) suppression tuning curve (STC) shows the minimum level of suppressor tone that is required to reduce DPOAE level by a fixed amount, as a function of suppressor frequency. Several years ago, Mills [J. Acoust. Soc. Am. 103, 507-523 (1998)] derived, theoretically, an approximately linear relationship between the tip-to-tail suppressor level difference on a DPOAE STC, and the gain of the cochlear amplifier, defined as the maximum increase in the active over the passive basilar membrane (BM) response. In this paper, preliminary data from adult human subjects are presented that establish a correlation between this tip-to-tail DPOAE STC difference and the threshold of hearing, the latter measured at the frequency of the f2 primary tone. Assuming that both suppression and the DPOAE are by-products of active, nonlinear BM dynamics, the above result suggests that threshold elevation in mild levels of hearing loss may be attributed, in part, to a reduction of cochlear amplifier gain, which is detectable with the suppression paradigm.