The Medial Olivocochlear Reflex Is Unlikely to Play a Role in Listening Difficulties in Children

Abstract

The medial olivocochlear reflex (MOCR) has been implicated in several auditory processes. The putative role of the MOCR in improving speech perception in noise is particularly relevant for children who complain of listening difficulties (LiD). The hypothesis that the MOCR may be impaired in individuals with LiD or auditory processing disorder has led to several investigations but without consensus. In two related studies, we compared the MOCR functioning of children with LiD and typically developing (TD) children in the same age range (7-17 years). In Study 1, we investigated ipsilateral, contralateral, and bilateral MOCR using forward-masked click-evoked otoacoustic emissions (CEOAEs; n = 17 TD, 17 LiD). In Study 2, we employed three OAE types: CEOAEs (n = 16 TD, 21 LiD), stimulus frequency OAEs (n = 21 TD, 30 LiD), and distortion product OAEs (n = 17 TD, 22 LiD) in a contralateral noise paradigm. Results from both studies suggest that the MOCR functioning is not significantly different between the two groups. Some likely reasons for differences in findings among published studies could stem from the lack of strict data quality measures (e.g., high signal-to-noise ratio, control for the middle ear muscle reflex) that were enforced in the present study. The inherent variability of the MOCR, the subpar reliability of current MOCR methods, and the heterogeneity in auditory processing deficits that underlie auditory processing disorder make detecting clinically relevant differences in MOCR function impractical using current methods.

Keywords: auditory processing disorder; listening difficulty; medial olivocochlear reflex; otoacoustic emissions.

Figure 1.

Schematic representation and temporal sequence of events for all OAE types employed in the study: (a) forward-masked CEOAE, (b) CEOAE, (c) SFOAE, and (d) DPOAE. Channels (Ch) indicate separate physical transducers: I = ipsilateral and C = contralateral. Numbers in the figure are duration (ms) of each epoch and trial across OAE types. Note that the sizes of each element in the figure are made disproportionate to their duration to show shorter events clearly. CEOAE = click-evoked otoacoustic emissions; SFOAE = stimulus frequency otoacoustic emissions; DPOAE = distortion product otoacoustic emissions.

Figure 2.

Data quality metrics. Data are plotted as violin plots in Panels (a) and (b). In Panel (a), the distribution of SNR across OAE types (from both studies) is plotted. In Panel (b), the distribution of data rejected due to enhancements in OAE level is plotted. In both panels, the “violin” colors differentiate the OAE types. For each color, darker shades are data from the TD group, and lighter shades are from the LiD group. The shape of the violin is based on the kernel density distribution fitted to the data (Hintze & Nelson, 1998). Included within each violin are traditional box plots where the white circle is the median, the thick black line around the white circle is the interquartile range, and the thin black line is the data range. The horizontal, colored, line is the mean. Individual colored circles within each violin are raw data. The OAE types are presented as x axis labels in both panels. CEOAE 1 and 2 are CEOAEs from Studies 1 and 2, respectively. CEOAE 1 is the mean of all three literalities from Study 1. DPOAE_m is mixed DPOAE, DPOAE_d is distortion component, and DPOAE_r is reflection component of the DPOAE. In Panel (c), a representative CEOAE sample from one participant (TD group) in the baseline and with-noise conditions, and the noise floor + 12 dB (original noise floor is 12 dB below the dashed line) is presented. Enhancements are highlighted with orange filled circles. Data points below the noise floor + 12 dB line and those with enhancements were rejected. SNR = signal-to-noise ratio; OAE = otoacoustic emissions; CEOAE = click-evoked otoacoustic emissions; SFOAE = stimulus frequency otoacoustic emissions; DPOAE = distortion product otoacoustic emissions; SPL = sound pressure level.

Figure 3.

Violin plot demonstrating tests for the MEMR. Panel (a) shows the change in click (Δstimulus level) across the three lateralities in Study 1, and Panel (b) shows SFOAE group delay in the with contralateral elicitor condition in Study 2. The dashed gray line in Panel (a) is the normalized stimulus level in the baseline condition (no forward masker). Violin colors differentiate the CEOAE laterality. For each color, darker shades are data from the TD group, and lighter shades are from the LiD group (see Figure 2 caption for details on violin plots). MEMR = middle ear muscle reflex; SFOAE = stimulus frequency otoacoustic emissions; TD = typically developing; LiD = listening difficulties.

Figure 4.

Study 1 MOCR effect across the three lateralities and the mBIC. In Panel (a), normalized mean MOCR inhibition (%), that is, ΔCEOAE, for the different lateralities is plotted. The mBIC is plotted in Panel (b). In Panel (b), the dashed gray line at 0 represents the condition ipsilateral + contralateral MOCR = bilateral MOCR. As such, negative values indicate larger bilateral MOCR, and positive values indicate smaller bilateral MOCR re: ipsilateral + contralateral MOCR. Violin colors differentiate the CEOAE laterality. For each color, darker shades are data from the TD group, and lighter shades are from the LiD group (see Figure 2 caption for details on violin plots). CEOAE = click-evoked otoacoustic emissions; mBIC = MOCR–binaural interaction component; TD = typically developing; LiD = listening difficulties.

Figure 5.

Temporal analysis. analysis of ΔCEOAE across different time scales. Within-epoch analysis is shown in the top row: Panels (a), (b), and (c) represent ipsilateral, contralateral, and bilateral elicitor conditions, respectively. Mean ΔCEOAE obtained in successive 2.5-ms temporal bins (x axis) is plotted for both TD (circles, darker shades) and LiD (squares, lighter shades). Across-epoch analysis is shown in the bottom row; Panels (d), (e), and (f) represent ipsilateral, contralateral, and bilateral elicitor conditions, respectively. Mean ΔCEOAE (for the entire epoch duration 5–20 ms) obtained in four successive epochs following elicitor cessation is plotted for both TD (circles, darker shades) and LiD (squares, lighter shades). In the bottom panels, time on x axis also includes the 2-ms silent period following elicitor cessation (see Figure 1). Error bars represent 1 SD. CEOAE = click-evoked otoacoustic emissions; TD = typically developing; LiD = listening difficulties.

Figure 6.

Study 2—MOCR effect across the three OAE types. The magnitude of MOC inhibition of OAEs (normalized change in level re: baseline elicitor-off condition) is plotted for all OAE types. Violin colors represent OAE type. For each color, darker shades are data from the TD group, and lighter shades are from the LiD group (see Figure 2 caption for details on violin plots). OAE = otoacoustic emissions; MOCR = medial olivocochlear reflex; CEOAE = click-evoked otoacoustic emissions; SFOAE = stimulus frequency otoacoustic emissions; DPOAE = distortion product otoacoustic emissions.