Development of f2/f1 ratio functions in humans

Towards the preferred stimulus parameters for distortion product otoacoustic emissions in adults: A preliminary study

BACKGROUND

 Although distortion product otoacoustic emissions (DPOAEs) are useful in evaluating cochlear outer hair cell function, determining the optimal stimulus parameters could result in a more reliable, sensitive and specific diagnostic tool across the range of DPOAE applications. Objectives: To identify which stimulus parameters warrant further investigation for eliciting the largest and most reliable DPOAEs in adult humans. Method: A single group, repeated measures design involving a convenience sample of 20 normal-hearing participants between 19 and 24 years of age. Results: Descriptive statistics and mixed model analyses suggested L1/L2 intensity levels of 65/65 dB sound pressure level (SPL) and 65/55 dB SPL, and f2/f1 ratios of 1.18, 1.20 and 1.22 elicited larger and more reliable DPOAEs in both ears. Conclusion: Further investigation of the 65/65 dB SPL and 65/55 dB SPL intensity levels and the 1.18, 1.20 and 1.22 f2/f1 ratios is warranted to determine the stimulus parameters for eliciting the largest and most reliable DPOAEs in adult humans across the range of DPOAE applications.

A systematic review of stimulus parameters for eliciting distortion product otoacoustic emissions from adult humans

OBJECTIVE

The objective of this study is to review the scientific literature to determine if a set of stimulus parameters can be described to elicit distortion product otoacoustic emissions (DPOAEs) of higher absolute level and/or greater reliability in healthy adult humans and higher sensitivity and specificity in adults with cochlear lesions.

DESIGN

Systematic review.

STUDY SAMPLE

Searches of four electronic databases yielded 47 studies that had used different parameters to elicit DPOAEs from within or between-groups of adult humans.

RESULTS

The wide range of stimulus parameters used in the reviewed studies saw a wide range of reported values for DPOAE level, reliability, and sensitivity and specificity to cochlear lesions.

CONCLUSION

The most commonly used stimulus parameters for eliciting DPOAEs from adult humans have included frequency ratios for the two primary tones (f₂/f₁) of between 1.04 and 1.4 and levels (L₁/L₂) of 65/55 dB SPL. The most commonly used parameters for eliciting DPOAEs of higher level in healthy adults appear to be linked to f₂/f₁ values between 1.20 and 1.22 and L₁/L₂ levels of 75/75 dB SPL. The stimulus parameters for eliciting DPOAEs of greater reliability in healthy adults and higher sensitivity and specificity in adults with cochlear lesions have yet to be clearly determined.

Sexing the baby: Part 1--What do we really know about sex differentiation in the first three years of life?

The most common paradigm used to analyze health differences between men and women, is to divide the body from the social environment. In such a model, the bodily contribution and the social contribution add up to 100%. A few health science researchers offer more sophisticated approaches. None, however, offer an intensive study of the first several years of life in order to offer a model which integrates biology and culture in a fashion that demonstrates the productive processes by which gender itself emerges. In this article, we identify the earliest known sex-related biological and behavioral differences in young infants, toddlers and their parents and indicate how these might relate to health and disease. We frame these differences using unifying concepts from the study of neuroplasticity and dynamic systems theory.

Comparing the optimal signal conditions for recording cubic and quadratic distortion product otoacoustic emissions

Odd- and even-order distortion products (DPs), evoked by two primary tones (f(1),f(2),f(1)<f(2)), represent different aspects of cochlear nonlinearity. The cubic and quadratic difference tones (CDT 2f(1)-f(2) and QDT f(2)-f(1)) are prominent representatives of the odd and even DPs. Distortion product otoacoustic emissions (DPOAEs) were measured within a primary level (L(1),L(2)) space over a wide range of f(2)f(1) ratios to compare the optimal signal conditions for these DPs. For CDT, the primary level difference decreased as L(1) increased with a rate proportional to the f(2)f(1) ratio. Moreover, the optimal ratio increased with L(1). A set of two formulas is proposed to describe the optimal signal conditions. However, for a given level of a primary, increasing the other tone level could maximize the QDT amplitude. The frequency ratio at the maximal QDT was about 1.3 and quite constant across different primary levels. A notch was found in the QDT amplitude at the f(2)f(1) ratio of about 1.22-1.25. These opposite behaviors suggest that the optimal recording conditions are different for CDT and QDT due to the different aspects in the cochlear nonlinearity. Optimizing the DPOAE recordings could improve the reliability in clinical or research practices.

Click-evoked otoacoustic emissions (CEOAEs) recorded from neonates under 13 hours old using conventional and maximum length sequence (MLS) stimulation

Maximum length sequence (MLS) stimulation allows click evoked otoacoustic emissions (CEOAEs) to be averaged at very high stimulation rates. This enables a faster reduction of noise contamination of the response, and has been shown to improve the signal-to-noise ratio (SNR) of CEOAEs recorded from adult subjects. This study set out to investigate whether MLS averaging can enhance the SNR of CEOAEs recorded in newborns within the first day after birth, and so improve the pass rates for OAE screening in this period, when false alarm rates are very high. CEOAEs were recorded in a neonatal ward from 57 ears in 37 newborns ranging from 6 to 13h old, using both conventional (50/s) and high rate (5000/s) MLS averaging. SNR values and pass rates were compared for responses obtained within equal recording times at both rates. MLS averaging produced an SNR improvement of up to 3.8dB, with the greatest improvement found in higher frequency bands. This SNR advantage resulted in pass rate improvement between 5% and 10%, depending on pass criterion. A significant effect of age was found on both SNR and pass rate, with newborns between 6 and 10h old showing significantly lower values than those tested between 10 and 13h after birth, as well as a much greater improvement due to MLS averaging. The findings show that MLS averaging can reduce false alarm rates by up to 15% in very young neonates in a neonatal ward setting.

Distortion product otoacoustic emissions for hearing threshold estimation and differentiation between middle-ear and cochlear disorders in neonates

Our aim in the present study was to apply extrapolated DPOAE I/O-functions [J. Acoust. Soc. Am. 111, 1810-1818 (2002); 113, 3275-3284 (2003)] in neonates in order to investigate their ability to estimate hearing thresholds and to differentiate between middle-ear and cochlear disorders. DPOAEs were measured in neonates after birth (mean age = 3.2 days) and 4 weeks later (follow-up) at 11 test frequencies between f2 = 1.5 and 8 kHz and compared to that found in normal hearing subjects and cochlear hearing loss patients. On average, in a single ear hearing threshold estimation was possible at about 2/3 of the test frequencies. A sufficient test performance of the approach is therefore suggested. Thresholds were higher at the first measurement compared to that found at the follow-up measurement. Since thresholds varied with frequency, transitory middle ear dysfunction due to amniotic fluid instead of cochlear immaturity is suggested to be the cause for the change in thresholds. DPOAE behavior in the neonate ears differed from that found in the cochlear hearing loss ears. From a simple model it was concluded that the difference between the estimated DPOAE threshold and the DPOAE detection threshold is able to differentiate between sound conductive and cochlear hearing loss.