Effect of contralateral acoustic stimulation on active cochlear micromechanical properties in human subjects: dependence on stimulus variables

Abstract

1. Outer hair cells (OHCs) have active micromechanical properties that are thought to be the origin of evoked otoacoustic emissions (EOAEs). In the present study, click-evoked otoacoustic emissions were recorded in humans with or without various contralateral acoustic stimulations. A previous study, concentrating on contralateral stimulation with broadband noise, had shown a decrease of the EOAE amplitude in humans. Results support a role for the efferent system in cochlear mechanics; indeed, medial efferent neurons of the olivocochlear bundle terminate on the OHCs. To obtain a better understanding of the medial efferent system functioning in humans, the present study looked at the contralateral suppressive effect as a function of stimulus parameters. 2. The study of the input-output function of the EOAE amplitude with and without a 50-dB SPL contralateral broadband noise showed that the suppressive effect was equivalent to a mean reduction of 3.77 dB. 3. For the EOAEs to tone pips, the contralateral suppressive effect was strongest when the contralateral ear stimuli were narrow bands that were centered around the central EOAE frequency. This frequency specificity disappeared for contralateral narrow band noise levels greater than 50 dB SPL. 4. The contralateral suppressive effect was also observed with transient contralateral sounds (nonfiltered clicks). Significant reductions of the EOAE amplitude were seen with contralateral click levels as low as 17.5 dB SL. Above this level, the EOAE amplitude decreased as the contralateral stimulus level increased. This effect was still present in subjects without any stapedial reflex, but absent in total unilateral hearing-loss subjects. Therefore this suppressive effect is unlikely to be due to alteration of the middle ear function or to transcranially conducted sound. 5. When the contralateral interclick interval exceeded 14.2 ms. the suppressive effect was smaller. With contralateral stimulus level maintained subjectively constant, the effect was found to disappear when the interclick interval was greater than 49.9 ms. A saturation of the contralateral suppressive effect was observed for click rates greater than 70/s (interclick interval less than 14.2 ms). 6. Our study confirms and specifies the contralateral sound suppression effect on cochlear mechanisms in humans, assessing the equivalent reduction, showing a frequency specificity and extending these findings to contralateral transient sounds. Any influence of the acoustic crosstalk was eliminated. A role played by middle ear muscles cannot be absolutely ruled out but is not necessary to produce such a contralateral suppressive effect (the effect being found in subjects after surgical removal of the stapedius muscle) and could not explain the frequency specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

Simultaneous Measurement of Noise-Activated Middle-Ear Muscle Reflex and Stimulus Frequency Otoacoustic Emissions

“…To date, the majority of studies using OAEs to study MOC reflex in humans have only indirectly addressed the problem of MEM reflex. For instance, Veuillet et al (1991Veuillet et al ( , 1992 inferred the lack of MEM contamination from the observation that similar changes in emissions were found in subjects with elevated or absent acoustic reflex thresholds. The observation that a broadband acoustic-noise activator generates more suppression of OAEs at low than high activator levels has been interpreted to mean that the effect of the MEM is negligible (Hood et al, 1996(Hood et al, , 2003Veuillet et al, 1991).…”

“…For instance, Veuillet et al (1991Veuillet et al ( , 1992 inferred the lack of MEM contamination from the observation that similar changes in emissions were found in subjects with elevated or absent acoustic reflex thresholds. The observation that a broadband acoustic-noise activator generates more suppression of OAEs at low than high activator levels has been interpreted to mean that the effect of the MEM is negligible (Hood et al, 1996(Hood et al, , 2003Veuillet et al, 1991). The observation that the effects of the acoustic activator are somewhat frequency specific (Liberman, 1989) has been used to argue against substantial MEM contamination ( Maison et al, 1997Maison et al, , 1999Mott et al, 1989;Collet et al, 1990).…”

“…First, some OAE probe stimuli themselves may elicit the MOC reflex, making the shift in the OAE smaller than it would otherwise be in the absence of this partial activation of the reflex by the probe. Second, the MOC activator is generally presented to the contralateral ear to avoid acoustic contamination of the OAE (Collet et al, 1990;Veuillet et al, 1991;Maison et al, 1997). Anatomical evidence suggests that the ipsilateral reflex is stronger than the contralateral reflex (Guinan et al, 1983;Robertson and Gummer, 1985;Warr, 1992), where Bipsilateral^refers to the case when activator and probe are presented in the same ear.…”

“…To date, the majority of studies using OAEs to study MOC reflex in humans have only indirectly addressed the problem of MEM reflex (Mott et al, 1989;Collet et al, 1990;Veuillet et al, 1991Veuillet et al, , 1992Hood et al, 1996Hood et al, , 2003Maison et al, 1997Maison et al, , 1999. The studies of Burns et al (1993) and Whitehead et al (1991) suggest that emissions may be sensitive to small, subclinical MEM contractions, making direct measurement desirable.…”

Measurement of the Distribution of Medial Olivocochlear Acoustic Reflex Strengths Across Normal-Hearing Individuals via Otoacoustic Emissions

“…De Ceulaer et al (2001) presented the first measured distribution of MOCR strengths across individuals using otoacoustic emissions (OAEs). However, it is uncer-tain how much their results are affected by MOC activity evoked by their test clicks (Veuillet et al 1991;Guinan et al 2003) and by their use of the Bnonlinear click method^, which misses the linear part of the MOCR effect. Furthermore, a major drawback of the De Ceulaer study is that no mention is made of how repeatable the measurements were on each individual.…”