Volume 117, Issue 5, May 2005
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
Distortion product otoacoustic emissions for hearing threshold estimation and differentiation between middle-ear and cochlear disorders in neonates117(2005); http://dx.doi.org/10.1121/1.1853101View Description Hide Description
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 and 4 weeks later (follow-up) at 11 test frequencies between 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.
117(2005); http://dx.doi.org/10.1121/1.1880792View Description Hide Description
Given that high-frequency hearing is most vulnerable to cochlear pathology, it is important to characterize distortion-product otoacoustic emissions (DPOAEs) measured with higher-frequency stimuli in order to utilize these measures in clinical applications. The purpose of this study was to explore the dependence of DPOAE amplitude on the levels of the evoking stimuli at frequencies greater than 8 kHz, and make comparisons with those data that have been extensively measured with lower-frequency stimuli. To accomplish this, DPOAE amplitudes were measured at six different frequencies (2, 5, 10, 12, 14, and 16 kHz), with a frequency ratio of 1.2, at five fixed levels (30 to 70 dB SPL) of one primary (either or while the other primary was varied in level (30 to 70 dB SPL). Generally, the level separation between the two primary tones generating the largest DPOAE amplitude (referred to as the “optimal level separation”) decreased as the level of the fixed primary increased. Additionally, the optimal level separation was frequency dependent, especially at the lower fixed primary tone levels SPL). In agreement with previous studies, the DPOAE level exhibited greater dependence on than on
Using the short-time correlation coefficient to compare transient- and derived, noise-evoked otoacoustic emission temporal waveforms117(2005); http://dx.doi.org/10.1121/1.1893285View Description Hide Description
Transient-evoked otoacoustic emissions (TEOAEs) and derived, noise-evoked otoacoustic emissions (derived-NEOAEs) were measured in seven normally hearing subjects. The evoked OAEs were all recorded at three excitation levels chosen to ensure that the OAE level curve compressive region was reached. The short-time correlation coefficient (STCC) was used to compare the OAE waveforms at different excitation levels, and thus estimate the time over which the response exceeds the noise level. The short-time correlation for TEOAEs is significant for longer than it is for NEOAEs, particularly in some individuals, and the STCC allows this to be quantified. This suggests that derived NEOAEs do not display the highly synchronized dominant frequencies often seen in TEOAEs. This has been confirmed by examining the derived frequency responses for the two types of excitation. Conventional TEOAEs thus appear to measure a combination of two conceptually different processes, while NEOAEs measure just one.
117(2005); http://dx.doi.org/10.1121/1.1880812View Description Hide Description
Two-tone distortion was measured in the intracochlear pressure in the base of the gerbil cochlea, close to the sensory tissue, where the local motions and forces of the organ of Corti can be detected. The measurements probe both the underlying nonlinear process that generates two-tone distortion, and the filtering and spreading of the distortion products. Some of our findings are as follows: (1) The observations were consistent with previous observations of two-tone distortion in BM motion [J. Neurophysiol. 77, 2385–2399 (1997); J. Neurophysiol. 78, 261–270 (1997)]. (2) Frequency sweeps show distortion product tuning and phase-versus-frequency behavior that is similar, but not identical, to single tone tuning. (3) The decay of distortion products with distance from the basilar membrane confirms the feasibility that they could drive the stapes by a direct fluid route, as proposed by Ren [Nat. Neurosci. 7, 333–334 (2004)]. (4) The phases of the distortion products within a single family (the group of distortion products generated by a single primary pair) in some cases alternated between and when referenced to the phases of the primaries. This behavior is predicted by a simple compressive nonlinearity.