Concurrent measures of contralateral suppression of transient-evoked otoacoustic emissions and of auditory steady-state responses

Abstract

Contralateral suppression of otoacoustic emissions (OAEs) is frequently used to assess the medial olivocochlear (MOC) efferent system, and may have clinical utility. However, OAEs are weak or absent in hearing-impaired ears, so little is known about MOC function in the presence of hearing loss. A potential alternative measure is contralateral suppression of the auditory steady-state response (ASSR) because ASSRs are measurable in many hearing-impaired ears. This study compared contralateral suppression of both transient-evoked otoacoustic emissions (TEOAEs) and ASSRs in a group of ten primarily older adults with either normal hearing or mild sensorineural hearing loss. Responses were elicited using 75-dB peak sound pressure level clicks. The MOC was activated using contralateral broadband noise at 60 dB sound pressure level. Measurements were made concurrently to ensure a consistent attentional state between the two measures. The magnitude of contralateral suppression of ASSRs was significantly larger than contralateral suppression of TEOAEs. Both measures usually exhibited high test-retest reliability within a session. However, there was no significant correlation between the magnitude of contralateral suppression of TEOAEs and of ASSRs. Further work is needed to understand the role of the MOC in contralateral suppression of ASSRs.

Figures

FIG. 1.

(Color online) Mean audiometric thresholds for the left and right ears. Error bars represent ±1 SEM. Results for the left and right ears are offset from each other at a given frequency to aid visualization.

FIG. 2.

(Color online) Schematic of the equipment setup for concurrent measurement of contralateral suppression of ASSRs and of TEOAEs. Stimulus outputs are represented by solid arrows. Input from the ER-10B+ microphone is represented by a dashed black arrow. Inputs from the electrode headstage and preamplifier are represented by the dotted arrows.

FIG. 3.

(Color online) Schematic of one interleaved presentation of stimuli. Click trains are shown in the top half of the panel for the right ear and broadband contralateral noise is shown in the bottom half of the panel for the left ear. The number of clicks displayed is reduced by a factor of 10 to aid visualization of individual click stimuli. Two stimulus conditions (no CAS and CAS) are shown, separated by a 2-s noise-alone interval (first pair of vertical dashed lines). The two stimulus conditions were repeated continuously, with 2 s of silence between repetitions (second pair of vertical dashed lines). Note that TEOAEs and ASSRs were measured concurrently for the duration of the recording.

FIG. 4.

(Color online) Recorded TEOAE and ASSR spectra (left and right panels, respectively) for one representative subject. Solid lines represent responses obtained in the no CAS condition. Dotted lines represent responses obtained in the CAS condition. The filled gray regions represent the recording noise floors.

FIG. 5.

Magnitudes of TEOAEs and ASSRs (top and bottom panels, respectively) for each individual subject. Responses in the no CAS and CAS conditions are represented by black and white bars, respectively. The recording noise floors are represented by gray bars; noise floors in the no CAS and CAS conditions are on the left and right side, respectively, for each individual subject. The magnitudes displayed here represent the mean computed across the two replicate measurements obtained from each subject.

FIG. 6.

Test–retest reliability of contralateral suppression of TEOAEs (left panel) and of ASSRs (right panel). Results are plotted as the contralateral suppression value obtained in the second measurement against that of the first measurement (note the different ordinate scales). The filled circles represent data from each individual subject. The dashed line represents a 1:1 correspondence between the results at each measurement. Both measures exhibited high test–retest reliability within a session.

FIG. 7.

Contralateral suppression of TEOAEs (black bars) and of ASSRs (hatched bars). Individual subject data are plotted to the left of the vertical dashed line. The mean data (+1 SEM) are plotted to the right of the dashed line. Note that Subject 6 showed close to 0 dB (−0.01 dB) of contralateral suppression of the ASSR and thus no hatched bar is apparent for this subject.

FIG. 8.

Association between contralateral suppression of TEOAEs and of ASSRs. The filled circles represent data from individual subjects. The dashed line represents a least-squares fit to the data. The correlation between the two measures was not significant.