Miguel Angel Aranda de Toro

Recovery of distortion-product otoacoustic emissions after a 2-kHz monaural sound-exposure in humans: Effects on fine structures

A better understanding of the vulnerability of the fine structures of distortion-product otoacoustic emissions (DPOAEs) after acoustic overexposure may improve the knowledge about DPOAE generation, cochlear damage, and lead to more efficient diagnostic tools. It is studied whether the DPOAE fine structures of 16 normal-hearing human subjects are systematically affected after a moderate monaural sound-exposure of 10 min to a 2-kHz tone normalized to an exposure level L(EX,8h) of 80 dBA. DPOAEs were measured before and in the following 70 min after the exposure. The experimental protocol allowed measurements with high time and frequency resolution in a 1/3-octave band centered at 3 kHz. On average, DPOAE levels were reduced approximately 5 dB in the entire measured frequency-range. Statistically significant differences in pre- and post-exposure DPOAE levels were observed up to 70 min after the end of the sound exposure. The results show that the effects on fine structures are highly individual and no systematic change was observed.

Is it necessary to penalize impulsive noise +5 dB due to higher risk of hearing damage?

It is studied whether the +5 dB penalty for impulsiveness established by ISO 1999:1990 accounts for a higher risk of noise-induced hearing loss. A total of 16 normal-hearing human subjects were exposed for 10 min to two types of binaural industrial-recordings: (1) a continuous broad-band noise normalized to L(EX,8 h)=80 dBA and (2) the combination of the previous stimulus with an impulsive noise normalized to L(EX,8 h)=75+5(db penalty)=80 dBA (peak level 117 dBC and repetition rate of 0.5 impacts per second). Distortion product otoacoustic emissions (DPOAEs) were measured in a broad frequency range before and in the following 90 min after the exposure. The group results show that the continuous exposure had a bigger impact on DPOAE levels, with a maximum DPOAE shift of approximately 5 dB in the frequency range of 2-3.15 kHz during the first 10 min of the recovery. No evident DPOAE shift is seen for the impulsive + continuous stimulus. The results indicate that the penalty overestimated the effects on DPOAE levels and support the concept that the risk of hearing loss from low-level impulses may be predicted on an equal-energy basis.

Changes in distortion product oto-acoustic emissions after exposure to continuous and impulsive noise

Temporary changes in the hearing of human subjects were monitored with distortion product otoacoustic emissions (DPOAEs) after control sound exposures in a laboratory. The objectives of the experiment were to investigate whether the +5~dB penalty for impulsiveness used in international standards and legislation correlates to a higher risk of hearing damage. Subjects were exposed to two types of binaural recordings consisting of a continuous broad-band noise-exposure normalized to LEX,8h = 80~dB and the interaction of the previous stimulus with a noise of impulsive character normalized to LEX,8h = 75 + 5~dB penalty = 80~dB. The results show that the effects on DPOAE levels from the two stimuli could be compared in terms of their total acoustic energy.

Recovery of distortion product otoacoustic emissions (DPOAE) after impulse vs. continuous equal-energy exposures

The correct assessment of impulse noise from occupational environments for hearing‐conservation purposes is still a controversial issue. Currently, no universally accepted standard defines impulse noise accurately nor does a standard method exist to measure impulses. Moreover, current impulse‐damage risk‐criteria suffer from lack of empirical data needed to quantify impulse noise exposures and assess potential damage. In this experiment human subjects are exposed to binaural recordings of noises from industrial environments. Stimuli consist of impulse noise, continuous noise, and combinations of impulse and continuous noise. Noise exposures are normalized to have the same energy (LAeq,8h= 80dB). The effects in the hearing of the subjects are monitored by measuring the recovery of the distortion product otoacoustic emissions (DPOAE) with high‐time resolution. The results can be used to investigate the validity of current assessment methods and descriptors of the temporal characteristics of sound exposures ...

Recovery of distortion product otoacoustic emissions (DPOAE) with high time-resolution from a moderate monaural-exposure to 2-kHz in human subjects

The amplitude of distortion product otoacoustic emissions (DPOAE) decreases temporarily after exposure to a sound of moderate level. These changes show similarities to the changes observed in absolute hearing thresholds after similar sound exposures. This paper presents the experimental protocol to study how DPOAEs in human subjects are affected after a monaural exposure of ten minutes to a pure tone of 2 kHz. The experimental protocol allows to measure fine structures of the DPOAE with high time‐resolution in a limited frequency range. Thus, the results give a detailed description of the DPOAE recovery process and can be used to develop a mathematical model of the recovery. This is the first approximation to study the recovery of more complex exposures. [Work supported by the Danish Research Council for Technology and Production.]

Influence of the sweeping direction of the primaries f1 and f2 in the assessment of distortion product otoacoustic emissions (DPOAEs) fine structure

It was studied if the sweeping direction of the primaries f1 and f2 influences fine structure measurements of the 2f1−f2 distortion product otoacoustic emission (DPOAE). Two different methodologies named DPOAE5ASC (ascending sweep) and DPOAE5DES (descending sweep) were implemented with the commercial system ILO96. Both methods perform fine structure measurements in the same frequency range (1.4–6 kHz) with L1/L2=65/45 dB, f2/f1=1.22 and 0.7 s averaging time per primary presented. DPOAE fine structures were measured in the right ear of 14 normal‐hearing subjects with both methods in a balanced experiment and without refitting the sound probe. Results showed that the two methods are highly repeatable and able to detect fine structures even in subjects with low S/N. However, when DPOAE5ASC measurements are compared with DPOAE5DES, fine structures appear shifted and the level contour is altered. A minor level difference was inadvertently induced due to differences in the level calibration procedure of the two...

Time characteristics of distortion product otoacoustic emissions recovery function after moderate sound exposure

Exposure to sound of moderate level temporarily attenuates the amplitude of distortion product otoacoustic emissions (DPOAEs). These changes are similar to the changes observed in absolute hearing thresholds after similar sound exposures. To be able to assess changes over time across a broad frequency range, a detailed model of the recovery time characteristics is necessary. In the present study, the methodological aspects needed in order to monitor changes in DPOAEs from human subjects measured with high time resolution are presented. The issues treated are (1) time resolution of the measurements, (2) number of frequency points required, and (3) effects in fine structures, are they affected with the exposure? [Work supported by the Danish Research Council for Technology and Production.]