Thesis: Cue evoked effects on tone detection in noise: influence of the medial olivocochlear system
Hearing in noisy environments is a difficult task made all the more challenging in individuals with hearing impairment. The cocktail party effect, a term coined in the late 50's, describes our ability to focus auditory attention on a specific sound (an individual speaker) and filter this out from background noise (a noisy cocktail party).
My research concerns a potential link between a subcortical auditory system known as the medial olivocochlear system (MOCS), and the formation of the auditory filter through modulation of activity of the outer hair cell (OHC) amplifier. The auditory attentional filter is characterised by a cue-probe experiment, in which a clearly audible pure tone cue is played just preceding a threshold tone. The detectability of the threshold tone is influenced primarily in the difference in frequency between the cue and the probe. If they are the same frequency, then detection is high, if they are of a different frequency then they become considerably harder to detect.
The MOCS is in an ideal position to help form this filter. It possesses both the tonotopic anatomy to aid in the detection of tones at the same frequency, as well as the ability to modulate OHC activity to aid in their detection.
My research is using otoacoustic emissions (OAE) suppression to characterise the strength of the MOCS, and correlating this with measures of strength of the attentional filter. In normal hearing participants, we hypothesise that individuals with stronger MOCS will have sharper, stronger attentional filters.
My research will continue using participants with hearing impairments. Different forms of hearing impairment give different views into the effect of the MOCS on hearing in noise. Finally, I will perform experiments in those with cochlear implants, as these individuals have no remaining targets for the MOCS, and therefore represent a population with no MOCS effects.
Why my research is important
Initial importance is simply to deepen our understanding of the mechanisms behind how human listeners focus auditory attention.
This understanding has a number of beneficial outcomes however. The first is in those with hearing impairment, especially those with sensorineural hearing loss and cochlear implants. A very common complaint in such individuals is difficulty understanding speech in noisy environments. It is possible that this is due to a diminished auditory attentional filter due to loss of MOCS function. We may be able to train, or compensate for this loss through other cortical pathways, such as the visual pathway in lip reading for example.
Another potential outcome is the improvement of cochlear implants to take the formation of these filters into account in their speech processors. A greater understanding of how the normal auditory system functions in noisy environments will enable improvements to be made here.