The medial olivocochlear bundle and speech-in-noise deficits
Target Investigator:
Thierry Morlet, PhD
Research Scientist
Mentors: H. Timothy Bunnell, Ph.D.
Jeffery L. Twiss, M.D., Ph.D.

In children, auditory processing disorder (APD) presents as difficulty processing speech despite audiometrically normal hearing. Commonly, this difficulty is most pronounced in the presence of competing background noise, which, unfortunately, represents most typical real-world listening situations. The causes of APD are not known, and in all likelihood, APD as broadly defined represents a family of auditory processing deficits stemming from multiple causes. The present proposal focuses on one possible cause for (or contribution to) APD: a failure in the way cortical and peripheral components of the auditory system interact when processing speech sounds in noise. This cortical-peripheral interaction is believed to involve both afferent nerve fibers from the cochlea and efferent nerve fibers which project through the medial olivocochlear nucleus to the cochlea. Moreover, existing data on the nature of the efferent system suggest that (a) it plays a role in improving the listener’s ability to detect signals in noise, and (b) in normally hearing individuals it mirrors the pattern of laterality that is typically observed for speech, that is, it appears to function more robustly for signals reaching the right ear. Our overall hypothesis is that the normal functioning of this efferent system is disrupted in children with APD, resulting in a system that performs poorly when stimuli are presented in noise, and fails to demonstrate the right ear advantage that is typical of a normally functioning efferent system. We will test this hypothesis with the following specific aims:


Specific Aim 1: Examine ear advantages and interhemispheric asymmetry in APD.

Hypothesis: Children with APD will fail to show both a right ear advantage and a left hemispheric advantage when processing speech, particularly in the presence of competing background noise.

Here, we will determine the ear advantage and interhemispheric asymmetries in children with APD vs. age-matched normal hearing children. We will use behavioral (dichotic listening paradigm) and electrophysiological measures (auditory event related potentials) for testing in quiet and in noise conditions.


Specific Aim 2: Measure asymmetry in the cochlear function and efferent pathways in APD.

Hypothesis: Peripheral asymmetries in cochlear function as measured by differences in the magnitude of otoacoustic emissions and their suppression will be directly correlated with more central asymmetries (as measured by dichotic listening and auditory event related potentials), and the correlation will reverse in children with APD in presence of noise.