Comparing otoacoustic emissions evoked by chirp transients with constant absorbed sound power and constant incident pressure magnitude

Abstract

Human ear-canal properties of transient acoustic stimuli are contrasted that utilize measured ear-canal pressures in conjunction with measured acoustic pressure reflectance and admittance. These data are referenced to the tip of a probe snugly inserted into the ear canal. Promising procedures to calibrate across frequency include stimuli with controlled levels of incident pressure magnitude, absorbed sound power, and forward pressure magnitude. An equivalent pressure at the eardrum is calculated from these measured data using a transmission-line model of ear-canal acoustics parameterized by acoustically estimated ear-canal area at the probe tip and length between the probe tip and eardrum. Chirp stimuli with constant incident pressure magnitude and constant absorbed sound power across frequency were generated to elicit transient-evoked otoacoustic emissions (TEOAEs), which were measured in normal-hearing adult ears from 0.7 to 8 kHz. TEOAE stimuli had similar peak-to-peak equivalent sound pressure levels across calibration conditions. Frequency-domain TEOAEs were compared using signal level, signal-to-noise ratio (SNR), coherence synchrony modulus (CSM), group delay, and group spread. Time-domain TEOAEs were compared using SNR, CSM, instantaneous frequency and instantaneous bandwidth. Stimuli with constant incident pressure magnitude or constant absorbed sound power across frequency produce generally similar TEOAEs up to 8 kHz.

Assessing Sensorineural Hearing Loss Using Various Transient-Evoked Otoacoustic Emission Stimulus Conditions

“…The stimulus level reported in the present study was based on the peak-to-peak equivalent sound pressure level (peSPL) across all three buffers, so that it was controlled by the peSPL for the simultaneous presentation condition. This is in contrast to the chirp stimulus level measure reported in Keefe et al (2016) and Keefe et al (2017), in which the peSPL was based on the chirp sound produced by the receiver driven by DAC1. Thus, the peSPLs in the present study are reported as about 14 dB higher than in those studies.…”

“…This finding is related to the fact that the power-weighting technique is designed to re-arrange the stimulus energy across frequencies, while maintaining a similar peSPL (Keefe et al (2017)). It should be noted that while the mean peSPL was essentially the same (within 0.2 dB) between the three stimulus methods, the mean SPL of the stimulus was roughly 2 dB greater for the power-weighted method (see Table 2, which also shows the standard error (SE) of the mean).…”

“…To produce the power-weighted chirp, the ambient conductance at the probe tip was obtained as the real part of the measured admittance at the probe tip. As explained in Keefe et al (2017), the chirp stimulus waveform (Figure 2, bottom left panel) was adjusted in amplitude at each time step so that the resulting absorbed sound power spectrum was approximately constant over the frequency range from 0.25 to 8 kHz. This power-weighted chirp stimulus was then scaled by a single gain factor applied to the DAC waveform to generate approximately the same peSPL in the ear as was measured using the unweighted chirp (i.e., the ambient chirp described above).…”

“…This is called an unweighted stimulus in the present study, and it is presented in both ambient pressure and TPP test conditions. Keefe et al (2017) generalized this approach to measure TEOAEs using a stimulus that has approximately constant absorbed sound power level across frequency. This is termed the power-weighted stimulus in the present study, for which a WB admittance measurement is required to calculate the absorbed power level based on an initial measurement in the ear canal using the unweighted stimulus.…”

“…A power-weighted stimulus controls for individual differences in ear-canal standing waves and in the absorbance of the middle ear (Keefe & Schairer 2011). Keefe et al (2017) reported TEOAE data for a group of adults with normal hearing using a power-weighted stimulus. The purpose of the present study was to apply these methods in a group of adults that included ears with normal hearing and ears with SNHL in order to assess the potential utility to predict the presence of SNHL.…”