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Within- and Across-Subject Variability of Repeated Measurements of Medial Olivocochlear-Induced Changes in Transient-Evoked Otoacoustic Emissions

Mertes, Ian B.; Goodman, Shawn S.

doi: 10.1097/AUD.0000000000000244
e-Research Articles

Objectives: Measurement of changes in transient-evoked otoacoustic emissions (TEOAEs) caused by activation of the medial olivocochlear reflex (MOCR) may have clinical applications, but the clinical utility is dependent in part on the amount of variability across repeated measurements. The purpose of this study was to investigate the within- and across-subject variability of these measurements in a research setting as a step toward determining the potential clinical feasibility of TEOAE-based MOCR measurements.

Design: In 24 normal-hearing young adults, TEOAEs were elicited with 35 dB SL clicks and the MOCR was activated by 35 dB SL broadband noise presented contralaterally. Across a 5-week span, changes in both TEOAE amplitude and phase evoked by MOCR activation (MOC shifts) were measured at four sessions, each consisting of four independent measurements. Efforts were undertaken to reduce the effect of potential confounds, including slow drifts in TEOAE amplitude across time, activation of the middle-ear muscle reflex, and changes in subjects’ attentional states. MOC shifts were analyzed in seven 1/6-octave bands from 1 to 2 kHz. The variability of MOC shifts was analyzed at the frequency band yielding the largest and most stable MOC shift at the first session. Within-subject variability was quantified by the size of the standard deviations across all 16 measurements. Across-subject variability was quantified as the range of MOC shift values across subjects and was also described qualitatively through visual analyses of the data.

Results: A large majority of MOC shifts in subjects were statistically significant. Most subjects showed stable MOC shifts across time, as evidenced by small standard deviations and by visual clustering of their data. However, some subjects showed within- and across-session variability that could not be explained by changes in hearing status, middle ear status, or attentional state. Simulations indicated that four baseline measurements were sufficient to predict the expected variability of subsequent measurements. However, the measured variability of subsequent MOC shifts in subjects was often larger than expected (based on the variability present at baseline), indicating the presence of additional variability at subsequent sessions.

Conclusions: Results indicated that a wide range of within- and across-subject variability of MOC shifts was present in a group of young normal-hearing individuals. In some cases, very large changes in MOC shifts (e.g., 1.5 to 2 dB) would need to occur before one could attribute the change to either an intervention or pathology, rather than to measurement variability. It appears that MOC shifts, as analyzed in the present study, may be too variable for clinical use, at least in some individuals. Further study is needed to determine the extent to which changes in MOC shifts can be reliably measured across time for clinical purposes.

The goal of this study was to quantify the variability of repeated measurements of transient-evoked otoacoustic emission-based measurements of the medial olivocochlear reflex in normal-hearing subjects. Most subjects showed stable results across a 5-week span; however, some showed high variability within and across sessions that did not appear to be due to changes in auditory function. In some cases, large changes in olivocochlear reflex results would need to occur before the change could be attributed to something other than measurement variability. The results suggested that such measurements may be too variable to be clinically feasible, at least in some subjects.Supplemental Digital Content is available in the text.

Department of Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa, USA.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and text of this article on the journal’s Web site (

Portions of this article were presented at the 2014 MidWinter Meeting of the Association for Research in Otolaryngology (ARO), February 22–26, 2014, and at the 2014 SoCal Hearing Conference, September 13, 2014. The first author received a travel award from the American Academy of Audiology Foundation to present the results at the ARO Meeting. This research served as part of the first author’s doctoral dissertation work.

All authors contributed equally to this work. I.B.M. designed and performed experiments, analyzed data, and wrote the paper and Supplemental Digital Content. S.S.G. designed experiments, analyzed data, and wrote the paper and Supplemental Digital Content.

The authors have no conflicts of interest to disclose.

Received June 12, 2015; accepted September 24, 2015.

Address for correspondence: Ian B. Mertes, Research Service (151), VA Loma Linda Healthcare System, 11201 Benton Street, Loma Linda, CA 92357, USA; and Loma Linda Veterans Association for Research and Education, Redlands, CA, USA. E-mail:

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