Article
Measurement of medial olivocochlear efferent activity in humans: comparison of different distortion product otoacoustic emissions-based paradigms
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Authors
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Wolfgang Wagner
- Tübingen Hearing Research Center, Dept. of Otolaryngology, Head and Neck Surgery, University of Tübingen, Germany
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Andreas Heyd
- Tübingen Hearing Research Center, Dept. of Otolaryngology, Head and Neck Surgery, University of Tübingen, Germany
| Published: | July 6, 2010 |
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Outline
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Introduction: The medial olivocochlear efferents (MOC) have been shown to be involved in different auditory functions including sound discrimination, selective attention to tones, sound localization and protection of the cochlea against acoustic overstimulation. Measurement of MOC activity using contralateral suppression (CS) of otoacoustic missions (OAE) is complicated by the pronounced dependence of measurement values from stimulus parameters. While a large variety of CS measurement paradigms has been described in literature, systematic comparison of different measurement strategies has not been reported as yet.
Methods: MOC activity was inferred by CS of distorsion product OAE (DPOAE). Four different paradigms employing different stimulus parameters were applied in 16 subjects (paradigm A: fix frequency and varied primary tone levels, B: varied frequency and fix levels, C: varied frequency and varied levels, D: measurement in DPOAE level minimum („dip“) of DPOAE fine structure).
Results: Mean absolute values of CS were 2.17 dB in paradigm A, 1.16 dB in paradigm B, 1.82 dB in paradigm C, and 2.6 dB in paradigm D, respectively. When stimulus parameters of the paradigms overlapped, comparable CS values occurred. However, when subjects were classified quantitatively according to MOC activity (i.e. ranking by amount of CS), the four paradigms produced different relative classifications for the majority of individuals.
Discussion and conclusion: Past literature has shown that intra-individual comparison of CS values over time is well feasible due to good CS repeatability. This study, on the other hand, indicates that inter-individual comparison of CS values and quantitative classification of subjects according to their MOC activity can be misleading. Thus, an “optimum” CS paradigm, which completely and unambiguously describes an individual´s MOC activity, is still to be defined. To date, among potential approaches to achieve that goal are i.) using individualized stimulus parameters by selecting stimulus frequencies and/or primary tone levels for each subject, based on DPOAE structure, ii.) covering the highest possible number of measurement points in each subject, using fine variation of stimulus parameters.
