Abstract:
The medial olivocochlear system is a descending neural pathway that originates in the
brainstem and innervates cochlear outer hair cells. Activation of this system has been shown to
modify active cochlear micromechanics, thereby modulating the flow of information travelling
from the peripheral auditory system to higher brain centres. Although the functional
significance of this system remains unclear, evidence suggests it plays a role in enhancing the
perception of sounds masked by noise. Data also suggests that medial olivocochlear activity is
amenable to auditory training, although research in this area is scarce and limited to the use of
unnatural stimuli.
The primary aim of this thesis was to investigate the effect of an auditory training
programme on listeners’ medial olivocochlear function as well as their ability to perceive
speech masked by noise. Transient and distortion product otoacoustic emissions measured with
and without contralateral acoustic stimulation were used as a physiological measure of medial
olivocochlear efferent activity. A novel masked whole-word recognition test and a commonly
used sentence recognition in babble test were used as measures of speech in noise perception
ability. Physiological and perceptual measurements were gathered before and after an auditory
training programme.
After undergoing training, listeners showed an improvement in the ability to perceive
words masked by noise, but no improvement in the ability to perceive sentences in multi-talker
babble. No significant change in otoacoustic emission measures was observed after training.
Results suggest that auditory training did not affect medial olivocochlear activity, as measured
by contralateral suppression of otoacoustic emissions. It is proposed that through training,
participants developed listening strategies independent of the medial olivocochlear system that
resulted in enhanced abilities to recognise words masked by constant noise, but not sentences
masked by multi-talker babble.