Comparisons of transient evoked otoacoustic emissions using chirp and click stimuli

Abstract

Transient-evoked otoacoustic emission (TEOAE) responses (0.7-8 kHz) were measured in normalhearing adult ears using click stimuli and chirps whose local frequency increased or decreased linearly with time over the stimulus duration. Chirp stimuli were created by allpass filtering a click with relatively constant incident pressure level over frequency. Chirp TEOAEs were analyzed as a nonlinear residual signal by inverse allpass filtering each chirp response into an equivalent click response. Multi-window spectral and temporal averaging reduced noise levels compared to a single-window average. Mean TEOAE levels using click and chirp stimuli were similar with respect to their standard errors in adult ears. TEOAE group delay, group spread, instantaneous frequency, and instantaneous bandwidth were similar overall for chirp and click conditions, except for small differences showing nonlinear interactions differing across stimulus conditions. These results support the theory of a similar generation mechanism on the basilar membrane for both click and chirp conditions based on coherent reflection within the tonotopic region. TEOAE temporal fine structure was invariant across changes in stimulus level, which is analogous to the intensity invariance of click-evoked basilar-membrane displacement data.

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

“…The peSPL of the equivalent click was 77.0 dB, or 13.7 dB higher than that of the chirp. In contrast, the total sound exposure level (SEL) (see Keefe et al, 2016) was the same for the chirp and equivalent click responses. For an individual ear, it is convenient to show the SEL spectrum levels of the stimuli and TEOAE response using a finer frequency resolution ( 1 6 octave frequencies between 0.7 and 8 kHz) so as to observe the individual properties, whereas a coarser frequency resolution was adopted in group analyses.…”

“…The (approximately) constant L Q chirp stimuli used in the present study are identical to those used in Keefe et al (2016), which were each generated in terms of a click stimulus with electrical input spectrum V ck ½k: Starting with a click stimulus, a reference voltage spectrum V ck ½k in the DFT of the electrical input signal applied to DAC1 generates a reference stimulus pressure spectrum P ck ½k in the measured data. For the allpass filter spectrum H½k used to produce either the positive or negative chirp, the electrical signal generating that chirp is calculated from the inverse DFT of V ch ½k ¼ H½k V ck ½k; and has a duration of N ¼ 1536 samples.…”

“…The SNR (in dB) is calculated over the L blocks in the time and frequency domains, as is the coherence synchrony modulus (CSM), which varies from 0 for a random noise signal to 1 for a deterministic signal (Keefe, 2012(Keefe, , 2014Keefe et al, 2016). The SNR is a measure of the ratio of TEOAE signal to noise energy, while CSM is a measure of the phase synchrony of the TEOAE.…”

“…The TEOAE measurements with the reference stimulus are those described in Keefe et al (2016). The constant L W (or powerweighted) stimulus design is described below for the chirp created by DAC1 applied to receiver 1.…”

“…The procedures to measure TEOAEs with (approximately) constant L Q stimulus are those described in Keefe et al (2016). Measurements were obtained in 58 adult ears with normal hearing.…”