Measuring 'Hearing Flexibility'
I am fascinated by the act of communicating with speech.
I have an idea in my head and I want to get it into your head, so I make a bunch of weird movements with my mouth in order to cause a pattern of changes in the air pressure around my head. These changes flow toward you on a wave and result in minute movements of molecules sitting in your ear canal. These movements result in vibrations of the ear drum, the ossicles (tiny bones in the ear that you may have learned as the hammer, anvil and stirrup), then the basilar membrane and finally the smallest of movements of little hairs (stereocilia) that lead to the firing of auditory nerve fibers.
Then your brain has to decode these neural responses into the idea that was in my head.
This is an amazingly complicated process, yet one that occurs with such ease it can become easily taken for granted.
Of course, there are times when it becomes apparent how difficult the task of communication actually is, such as when there is substantial background noise (as in a restaurant) or if the speaker has a strong accent.
Listeners appear to differ substantially in their ability to understand speech in these challenging conditions.
Of course, some individuals have even greater obstacles to understanding speech, such as profound hearing loss.
One of the marvels of modern medicine has been the development of the cochlear implant — a bionic ear — that can be used by those individuals with deafness or a profound hearing loss. The bionic ear receives sounds from the surrounding environment through an external microphone and transfers them directly to the auditory nerve as electrical impulses. The result is far from clear speech, akin to a harsh whisper.
While the bionic ear has helped many people, there also are substantial differences in how well people perform listening to speech through these devices. This leaves one to wonder why there are such large individual differences in people's abilities to understand speech in challenging listening situations, whether they have normal or impaired hearing.
My dissertation research focuses directly on this question of explaining the variation in people's ability to understand degraded speech. In particular, I have used a simulation of the sound that comes from a cochlear implant to degrade speech and present it to individuals with normal hearing.
This allows me to look at variability in performance without any differences in hearing ability or possible co-existing neural problems.
My hypothesis is that these differences in speech performance are related to our general ability to shift attention to aspects of sound that are reliable in a particular listening environment. The proposal is that this ability varies in the human population and people who are high in this "hearing flexibility" will be better at dealing with speech in noise, foreign accents, rapid speakers, and … the degraded sounds from the bionic ear.
We currently do not have a standard way of measuring "hearing flexibility." That is one of my goals for my dissertation and the work that will follow my hopefully successful defense of the dissertation.
Such a measure may prove to be useful for predicting outcomes for the use of hearing aids and cochlear implants. In addition, it will begin to shed light on how all of us manage to comprehend each other most of the time despite the innumerable challenges of communicating with sound.
Kathy Carbonell is a doctoral candidate in the UA's Department of Speech, Language and Hearing Sciences. Carbonell's dissertation co-chairs are Huanping Dai, an associate professor in the Department of Speech, Language and Hearing Sciences, and Andy Wedel, an associate professor in the Department of Linguistics. Carbonell anticipates that she will complete her program at the UA in December 2015. After graduation, she plans to continue developing her current line of research and pursue either a postdoctoral position or an academic position that would enable her to teach.
Photography: Beatriz Verdugo/UANews
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