No Change in Medial Olivocochlear Efferent Activity during an Auditory or Visual Task: Dual Evidence from Otoacoustic Emissions and Event-Related Potentials

Abstract

The medial olivocochlear (MOC) system is thought to be responsible for modulation of peripheral hearing through descending (efferent) pathways. This study investigated the connection between peripheral hearing function and conscious attention during two different modality tasks, auditory and visual. Peripheral hearing function was evaluated by analyzing the amount of suppression of otoacoustic emissions (OAEs) by contralateral acoustic stimulation (CAS), a well-known effect of the MOC. Simultaneously, attention was evaluated by event-related potentials (ERPs). Although the ERPs showed clear differences in processing of auditory and visual tasks, there were no differences in the levels of OAE suppression. We also analyzed OAEs for the highest magnitude resonant mode signal detected by the matching pursuit method, but again did not find a significant effect of task, and no difference in noise level or number of rejected trials. However, for auditory tasks, the amplitude of the P3 cognitive wave negatively correlated with the level of OAE suppression. We conclude that there seems to be no change in MOC function when performing different modality tasks, although the cortex still remains able to modulate some aspects of MOC activity.

Keywords: EEG; P3; attention; contralateral acoustic stimulation; event-related potentials; medial olivocochlear efferent system; otoacoustic emissions.

Figure 1

Schematic of measurement setup. TEOAE, transiently evoked otoacoustic emission; CAS+, contralateral acoustic stimulation on; CAS-, contralateral acoustic stimulation off; ERP, event-related potential.

Figure 2

Stimuli used for the visual paradigm as presented on a monitor screen. (A) standard; (B) Deviant. The background grey field is 10 × 10 cm, the stimulus is an aqua square 1.7 × 1.7 cm.

Figure 3

Example of application of matching pursuit. (A) TEOAE signal without CAS (grey) with the strongest resonant mode (superimposed, black) detected by matching pursuit, the highest energy single-frequency component of the TEOAE; (B) The same resonant mode (grey) with superimposed mode obtained from TEOAE with CAS (black), the amplitude is now slightly decreased; (C) The point in the time–frequency plane where the resonant mode has maximum amplitude.

Figure 4

Grand-average ERPs for all subjects recorded during the auditory task (black lines) and the visual task (grey lines). In both tasks the ERPs are synchronized to auditory stimuli. The consecutive plots show ERPs at Fz, Cz, and Pz electrodes, respectively. P3 is evident in responses to stimuli during the auditory task but, because of the synchronization arrangement, seems to be absent during the visual task.

Figure 5

Average suppression levels for TEOAEs measured in a 2.5–20 ms window under auditory and visual attention conditions. (A) Suppression expressed in dB; (B) Suppression expressed as % change in the signal. Whiskers indicate standard errors. There were no statistically significant differences between any of the data (p > 0.05).

Figure 6

Average suppression levels for TEOAEs measured in an 8–18 ms window under auditory and visual attention conditions. (A) Suppression expressed in dB; (B) Suppression expressed as % change in the signal. Whiskers indicate standard errors. There were no statistically significant differences between any of the data (p > 0.05).

Figure 7

Suppression of resonant modes detected by matching pursuit for auditory and visual attention conditions. (A) Average suppression for TEOAE main resonant mode found by matching pursuit as shown in Figure 3. Whiskers indicate standard errors. There were no statistically significant differences between any of the data (p > 0.05); (B) Time–frequency positions of resonant modes used for calculations.

Figure 8

Individual data for all subjects of MOC reflex during visual and auditory tasks, and shown in order of suppression level calculated as raw dB effect. (A) Raw dB effect; (B) Normalized % effect. Above the results for each subject is a letter indicating which modality gave the higher effect, i.e., a, auditory and v, visual.

Figure 9

Example of multiple repeats of the experiment in a single subject. (A) Raw dB effect; (B) Normalized % effect. Above the results for each run is a letter indicating which modality gave the higher effect, i.e., a, auditory and v, visual.

Figure 10

Combined ERP and TEOAE results. (A) P3 amplitude (while performing an auditory task) grouped according to whether TEOAE suppression was stronger for that task (circles, average for subjects who had stronger suppression during the auditory task and triangles, average for subjects who had stronger suppression during the visual task). Suppressions are calculated in both dB and % change in signal; (B) TEOAE suppression (as a % change in signal) during an auditory task plotted against P3 amplitude at the Cz electrode. P3 amplitude (during the auditory task) negatively correlates with the level of suppression.

Figure 11

Average noise levels (A) and percent of rejected trials (B), for four modes, i.e., reference 1 and 2 (squares), auditory (circles), visual (triangles). Ref 1, reference 1; Ref 2, reference 2; Aud, auditory task; Vis, visual task.