Relationship between medial‐olivocochlear reflex strength and masked thresholds.

Abstract

Otoacoustic emission amplitude is reduced by contralateral acoustic stimulation (CAS). This effect is produced by the medial‐olivocochlear (MOC) reflex. Past studies have shown that the MOC reflex is related to listening in noise and selective attention. The present study examined the relationship between the MOC reflex and masked thresholds in 14 normally hearing adults. Detection thresholds were determined for a 1000‐Hz, 300‐ms tone presented simultaneously with a 300‐ms masker. Three masking conditions in which energetic or informational masking predominate were investigated. DPOAEs were evoked from 500–4000 Hz with primary tones swept in frequency at 8 s/oct, using a fixed f2/f1 ratio of 1.22 at 65/55 dB sound pressure level. The MOC reflex and MOC‐shift were measured at DPOAE fine structure maxima at 948 and 1091 Hz with and without CAS. An inverse fast‐Fourier transform was performed to evaluate MOC effects on individual DPOAE components. Preliminary data analyzes showed MOC activity to be correlated with masked thresholds for both indices of medial efferent function. Most notably, higher masked thresholds for the random and broadband conditions were associated with a stronger MOC reflex for DPOAE maxima around 948 Hz. These results suggest that MOC activation plays a role in selective listening.