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. 2009 Mar;125(3):1584-94.
doi: 10.1121/1.3068442.

Considering distortion product otoacoustic emission fine structure in measurements of the medial olivocochlear reflex

Carolina Abdala  1 , Srikanta K Mishra, Tracy L Williams
Affiliations

Considering distortion product otoacoustic emission fine structure in measurements of the medial olivocochlear reflex

Carolina Abdala et al. J Acoust Soc Am. 2009 Mar.

Abstract

In humans, when the medial olivocochlear (MOC) pathway is activated by noise in the opposite ear, changes in distortion product otoacoustic emission (DPOAE) level, i.e., the MOC reflex, can be recorded in the test ear. Recent evidence suggests that DPOAE frequency influences the direction (suppression/enhancement) of the reflex. In this study, DPOAEs were recorded at fine frequency intervals from 500 to 2500 Hz, with and without contralateral acoustic stimulation (CAS) in a group of 15 adults. The MOC reflex was calculated only at DPOAE frequencies corresponding to peaks in the fine structure. Additionally, inverse fast-Fourier transform was conducted to evaluate MOC effects on individual DPOAE components. Results show the following: (1) When considering peaks only, the mean MOC reflex was -2.05 dB and 97% of observations reflected suppression, (2) CAS reduced distortion characteristic frequency component levels more than overlap component levels, and (3) CAS produced an upward shift in fine structure peak frequency. Results indicate that when the MOC reflex is recorded at DPOAE frequencies corresponding to fine structure maxima (i.e., when DPOAE components are constructive and in phase), suppression is reliably observed and level enhancement, which probably reflects component mixing in the ear canal rather than strength of the MOC reflex, is eliminated.

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Figures

Figure 1
Figure 1
DPOAE fine structure and noise floor from four randomly selected adult subjects. Panels (a) and (d) are from adults with strong fine structure and pronounced minima. Panels (b) and (c) in contrast show relatively poor-to-fair fine structure, with more shallow minima and more poorly defined peaks.
Figure 2
Figure 2
Mean DPOAE level at four f2 center frequencies in 15 normal-hearing adults. Data were collected for each subject during two separate runs (trials 1 and 2) within the same test session. Error bars reflect ±1 s.d.
Figure 3
Figure 3
Mean DPOAE fine structure spacing ratio and depth as a function of DP frequency in 15 adults. Data were collected for each subject during two separate runs (trials 1 and 2) within the same test session. Error bars reflect ±1 s.d.
Figure 4
Figure 4
Upper panel: Mean DP component level (overlap and CF) as a function of DP frequency in 15 adults. Data from trials 1 and 2 are combined. Lower panel: IFFT level output from one adult subject showing composite DPOAE level recorded in the ear canal, as well as overlap and CF component levels.
Figure 5
Figure 5
Mean DPOAE fine structure spacing ratio (upper panel) and depth (lower panel) as a function of DP frequency in 15 adult subjects. The parameter is absence or presence of CAS. The filled squares represent no-CAS and the open squares represent +CAS. Trials 1 and 2 data are combined. Error bars reflect ±1 s.d.
Figure 6
Figure 6
Upper panel: Mean difference scores reflecting the level difference between overlap and CF components as a function of DP frequency. The filled triangles represent no-CAS and the open triangles represent +CAS. Lower panel: Mean level for the overlap and CF components in no-CAS and +CAS conditions. Error bars reflect ±1 s.d.
Figure 7
Figure 7
Mean MOC reflex (defined as the difference between DPOAE level in no-CAS and +CAS conditions) calculated at DPOAE fine structure maximum frequencies only and shown as a function of DP frequency. Data were collected during two separate trials conducted within the same test session for 15 adults. Error bars reflect ±1 s.d.
Figure 8
Figure 8
DPOAE fine structure for four adult subjects with no-CAS, which is depicted with a solid black line, and in +CAS, which is depicted by a dashed gray line.
Figure 9
Figure 9
DPOAE fine structure from the two adult subjects also shown in panels (d) and (a) of Fig. 8. The no-CAS condition is depicted with a solid black line and +CAS with a dashed line. The corresponding MOC reflex (gray solid line) is superimposed on fine structure and referenced to the right axis.
Figure 10
Figure 10
Mean MOC shift (defined as an upward shift in fine structure peak frequency with the presentation of CAS) as a function of DP frequency for 15 adult subjects. Error bars reflect ±1 s.d.
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References

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