Volume 119, Issue 4, April 2006
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
Resonant modes in transiently evoked otoacoustic emissions and asymmetries between left and right ear119(2006); http://dx.doi.org/10.1121/1.2178718View Description Hide Description
A number of single-frequency resonant modes in click evoked otoacoustic emissions(OAEs) was investigated. The OAE modes were identified by means of an adaptive approximation method based on the matching pursuit (MP) algorithm. The signals were decomposed into basic waveforms coming from a very large and redundant dictionary of Gabor functions. The study was performed on transiently evoked otoacoustic emissions (TEOAEs) from left and right ears of 108 subjects. The correspondence between waveforms found by the procedure and resonant modes was shown (both for simulated noisy data and for single-person TEOAEs). The decomposition of TEOAEs made distinction between short and long-lasting components possible. The number of main resonant modes was studied by means of different criteria and they all led to similar results, indicating that the main features of the signal are explained on average by 10 waveforms. The same number of resonant modes for the right ear accounted for more energy than for the left ear.
119(2006); http://dx.doi.org/10.1121/1.2173517View Description Hide Description
The operating point (OP) of outer hair cell (OHC) mechanotransduction can be defined as any shift away from the center position on the transduction function. It is a dc offset that can be described by percentage of the maximum transduction current or as an equivalent dc pressure in the ear canal. The change of OP can be determined from the changes of the second and third harmonics of the cochlear microphonic (CM) following a calibration of its initial value. We found that the initial OP was dependent on sound level and cochlear sensitivity. From CM generated by a lower sound level at SPL to avoid saturation and suppression of basal turn cochlear amplification, the OHC OP was at constant 57% of the maximum transduction current (an ear canal pressure of ). To perturb the OP, a constant force was applied to the bony shell of the cochlea at the best frequency location using a blunt probe. The force applied over the scala tympani induced an OP change as if the organ of Corti moved toward the scala vestibuli (SV) direction. During an application of the constant force, the second harmonic of the CM partially recovered toward the initial level, which could be described by two time constants. Removing the force induced recovery of the second harmonic to its normal level described by a single time constant. The force applied over the SV caused an opposite result. These data indicate an active mechanism for OHC transduction OP.
119(2006); http://dx.doi.org/10.1121/1.2180533View Description Hide Description
The development of the auditory brainstem response was studied to quantitatively assess its dependence on stimulus frequency and level. Responses were not observed to stimuli on P12, however, the full range of responsive frequencies included in the study was observed by P14. Response thresholds were high on P12, exceeding SPL for all stimuli tested. The rate of threshold development increased progressively for stimulus frequencies between and , with the most rapid changes occurring at frequencies . Adultlike thresholds were observed by P18. Response latencies and interpeak intervals matured rapidly over the course of the second and third postnatal weeks and did not achieve adultlike characteristics until after P18. Latencies of higher-order peaks were progressively and sequentially delayed relative to wave I. Wave I amplitudes developed nonmonotonically, growing during the first and stabilizing at adult values by . Slopes of wave I amplitude-and latency-level curves were significantly steeper than those of adults during the neonatal period and the outcome of input-output analyses, as well as frequency-specific maturational profiles, support developmental models in which function initially matures in the mid-frequency range and proceeds, simultaneously, in both apical and basal directions.