Olivocochlear Efferent Activity Is Associated With the Slope of the Psychometric Function of Speech Recognition in Noise

Abstract

Objectives: The medial olivocochlear (MOC) efferent system can modify cochlear function to improve sound detection in noise, but its role in speech perception in noise is unclear. The purpose of this study was to determine the association between MOC efferent activity and performance on two speech-in-noise tasks at two signal-to-noise ratios (SNRs). It was hypothesized that efferent activity would be more strongly correlated with performance at the more challenging SNR, relative to performance at the less challenging SNR.

Design: Sixteen adults aged 35 to 73 years participated. Subjects had pure-tone averages ≤25 dB HL and normal middle ear function. High-frequency pure-tone averages were computed across 3000 to 8000 Hz and ranged from 6.3 to 48.8 dB HL. Efferent activity was assessed using contralateral suppression of transient-evoked otoacoustic emissions (TEOAEs) measured in right ears, and MOC activation was achieved by presenting broadband noise to left ears. Contralateral suppression was expressed as the decibel change in TEOAE magnitude obtained with versus without the presence of the broadband noise. TEOAE responses were also examined for middle ear muscle reflex activation and synchronous spontaneous otoacoustic emissions (SSOAEs). Speech-in-noise perception was assessed using the closed-set coordinate response measure word recognition task and the open-set Institute of Electrical and Electronics Engineers sentence task. Speech and noise were presented to right ears at two SNRs. Performance on each task was scored as percent correct. Associations between contralateral suppression and speech-in-noise performance were quantified using partial rank correlational analyses, controlling for the variables age and high-frequency pure-tone average.

Results: One subject was excluded due to probable middle ear muscle reflex activation. Subjects showed a wide range of contralateral suppression values, consistent with previous reports. Three subjects with SSOAEs had similar contralateral suppression results as subjects without SSOAEs. The magnitude of contralateral suppression was not significantly correlated with speech-in-noise performance on either task at a single SNR (p > 0.05), contrary to hypothesis. However, contralateral suppression was significantly correlated with the slope of the psychometric function, computed as the difference between performance levels at the two SNRs divided by 3 (decibel difference between the 2 SNRs) for the coordinate response measure task (partial rs = 0.59; p = 0.04) and for the Institute of Electrical and Electronics Engineers task (partial rs = 0.60; p = 0.03).

Conclusions: In a group of primarily older adults with normal hearing or mild hearing loss, olivocochlear efferent activity assessed using contralateral suppression of TEOAEs was not associated with speech-in-noise performance at a single SNR. However, auditory efferent activity appears to be associated with the slope of the psychometric function for both a word and sentence recognition task in noise. Results suggest that individuals with stronger MOC efferent activity tend to be more responsive to changes in SNR, where small increases in SNR result in better speech-in-noise performance relative to individuals with weaker MOC efferent activity. Additionally, the results suggest that the slope of the psychometric function may be a more useful metric than performance at a single SNR when examining the relationship between speech recognition in noise and MOC efferent activity.

Trial registration: ClinicalTrials.gov NCT02574247.

Conflict of interest statement

Financial Disclosures/Conflicts of Interest: The authors have no conflicts of interest to disclose.

Figures

Fig. 1

Box plots of audiometric thresholds. The bottom and top of each box represents the first and third quartiles, respectively. The horizontal line within each box represents the median. The lower and upper vertical lines extend to the minimum and maximum values, respectively.

Fig. 2

Schematic of stimuli presentation in the no CAS and CAS conditions. Clicks and CAS are shown in the top and bottom of the figure, respectively. Amplitude is displayed in arbitrary units. The two pairs of dashed vertical lines represent the 2-s interval of noise alone and silence, respectively, to allow for the onset and offset of the MOCR. The number of clicks displayed in the figure is reduced so that individual click stimuli can be visualized. The figure was adapted from Mertes & Leek (2016). CAS indicates contralateral acoustic stimulation; MOCR indicates medial olivocochlear reflex.

Fig. 3

Example of mean TEOAE waveforms (left panel) and spectra (right panel) for one representative subject. TEOAE amplitudes and magnitudes decreased in the presence of contralateral noise, as expected. In both panels, black and gray solid lines represent responses in the no CAS and CAS conditions, respectively. In the right panel, the thin black and gray dotted lines represent the recording noise floors in the no CAS and CAS conditions, respectively. TEOAE indicates transient-evoked otoacoustic emission; CAS indicates contralateral acoustic stimulation; mPa indicates millipascal.

Fig. 4

Changes in speech perception scores across SNRs for the CRM (left panel) and IEEE (right panel) tests. Each line represents performance for a different individual subject. The difference in percent correct at each SNR was divided by 3 to yield the slopes of the individual psychometric functions. SNR indicates signal-to-noise ratio; CRM indicates coordinate response measure; IEEE indicates Institute of Electrical and Electronics Engineers.

Fig. 5

Associations between contralateral suppression and speech-in-noise performance. Left and right columns display results for the CRM and IEEE tests, respectively. The top and middle rows display percentage correct at the SNR displayed in the top left corner of each panel. The bottom row displays results for the slopes of the psychometric functions. Spearman correlation coefficients (rs) and partial correlation coefficients (rsp) are displayed in the top right corner of each panel. Asterisks denote correlations that were significant at p < 0.05. CRM indicates coordinate response measure; IEEE indicates Institute of Electrical and Electronics Engineers; SNR indicates signal-to-noise ratio.