Rodrigo Pizarro Ordoñez

Overexposure effects of a 1-kHz tone on the distortion product otoacoustic emission in humans

The effects of overexposure on the properties of distortion product otoacoustic emissions (DPOAEs) are investigated. In total, 39 normal-hearing humans were monaurally exposed to a 1-kHz tone lasting for 3 min at an equivalent threshold sound-pressure level of 105.5 dB. The effects of overexposure were studied in two experiments (1) on the broadband DPOAE and (2) on the DPOAE fine structure, measured using a higher frequency resolution in a narrower frequency range. The obtained DPOAE shifts were compared to temporary threshold shift (TTS) obtained after a similar exposure. Similarities between DPOAE shifts and TTS were found in the affected frequency range and the time course of recovery. The amount of TTS was higher in the early recovery time (1-4-min postexposure), but similar to the DPOAE shift (even in absolute terms) at later recovery times (5-20-min postexposure). The DPOAE fine structure was not systematically changed after the exposure.

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.

Stimulus ratio dependence of low-frequency distortion-product otoacoustic emissions in humans

Active amplifiers within the cochlea generate, as a by-product of their function, distortion-product otoacoustic emissions (DPOAEs) in response to specific two-tone stimuli. Focus has been on invoking emissions in a mid-frequency range from ∼0.5 to 4 kHz. The present study investigates stimulus parameters of the DPOAE at 2f1-f2 frequencies below 0.5 kHz. Eighteen out of 21 young human adults screened had audiometrically normal hearing for inclusion in the experiment. DPOAEs were measured with pure-tone stimuli in four configurations: f2 fixed around 2.13 kHz, f2 fixed around 0.53 kHz, 2f1-f2 fixed at 1.23 kHz and 0.25 kHz. Eight stimulus ratios, f2/f1, and three stimulus sound pressure levels, L1/L2, were measured in each configuration. Trends in ratio-magnitude responses for the mid-frequency DPOAE agree with those reported in previous literature. DPOAEs are not limited to distortion frequencies >0.5 kHz, but the stimulus ratio invoking the largest DPOAE in the mid-frequency range does not do so in the low-frequency range. Guiding the ratio according to the equivalent rectangular bandwidth of auditory filters maintains the DPOAE level.

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.

Effects of personal stereo use: pilot results from 20 university students

Modern personal stereo systems have the ability to store thousands of music files in small, relatively low‐cost, compact devices. The popularity and widespread presence of the MP3 player cannot go unnoticed in contemporary society. Given a sufficient noise level and listening duration, consumers are at risk of developing a noise‐induced hearing loss. A study into the effects of personal stereo use will be carried out with the intention of investigating common noise exposure levels in realistic settings, user listening habits and the hearing status in a group of listeners. Noise exposure levels are to be obtained by using the manikin technique described in the ISO 11904‐2 standard. The questionnaire to be presented to interested participants is designed to report personal stereo listening habits and to screen subjects for the hearing status evaluation. The hearing status of selected subjects will be evaluated through the use of conventional and possibly extended high‐frequency audiometry, transient‐evoked ...

A pilot study of phase-evoked acoustic responses from the ears of human subjects

Otoacoustic emissions (OAEs) evoked by pure tones lock onto the phase of the stimulus at the place of their generation in the cochlea. The effects of phase transitions in a pure tone stimulus on OAEs have not been investigated. By combining responses to pure tones with smooth phase transitions, phase-evoked residual responses (PERRs) were extracted from nine normal-hearing subjects. Five of them had PERRs in at least 18 of 36 parameter conditions expected to yield a response. PERRs do not have a straightforward dependence on stimulus parameters, but their general prevalence suggests a temporary decoupling between stimulus and OAE phase – between 5 and 10 ms. Since the stimulus is narrow in the frequency domain, the PERR may reflect the dynamic behavior of localized regions of OAE generators.

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.

Changes in oto-acoustic emissions after exposure to live music

Distortion Product Oto-acoustic Emissions (DPOAE) and Transient Evoked Oto-acoustic Emissions (TEOAE) were measured in subjects before and after attendance to live music. The changes measured were compared to the exposure levels measured at the position of the subject. The main objectives of this experiment were two fold: 1) to assess the validity of the proposed measurement protocol to measure changes in DPOAE and TEOAE after a concert; 2) to test the reliability of the oto-acoustic emission measurement system under field conditions; Initial results shows that it is possible to measure changes in hearing after exposures of relative short duration (<1.5 hours). There are large individual differences both in sound exposure levels as well as in the changes on oto-acoustic emissions produced by similar exposures. Current results will be presented.

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.]