Perceptual measures and consequences
of cochlear nonlinearities
The inner ear, or cochlea, is the first stage of processing along
the auditory pathways. It is where sound energy is transformed into
neural spikes, which are transmitted along the auditory nerve to
the brain. Most cases of hearing impairment involve some damage
to the cochlea. This project has two main aims:
- Characterize cochlear hearing loss using perceptual measures.
It is not possible to make direct measures of how a cochlea is
responding in humans, so we are developing indirect behavioral
tests. Accurate assessments of cochlear function will provide
insight into what changes need to be compensated for in hearing
aids, and could provide a useful diagnostic tool in the clinic.
- Determine the perceptual consequences of cochlear processing.
Many of the difficulties experienced by hearing-impaired people
(such as understanding speech in noisy backgrounds) are caused
by changes in the cochlea. We use behavioral testing coupled with
quantitative modeling of cochlear function, to assess the effect
of normal and impaired cochlear processing on perception.
Selected publication:
Oxenham,
A. J., and Bacon, S. P. (2003). "Cochlear compression: Perceptual
measures and implications for normal and impaired hearing,"
Ear Hear. 24, 352-366.
Pitch perception
Pitch, along with loudness and timbre, is one of the fundamental
auditory percepts. It is crucial for our appreciation of music and
plays a vital role is speech perception. Most importantly perhaps,
differences in pitch are used by the auditory system to segregate
sounds. Our work concentrates on the perception of multiple pitches
in normal-hearing and hearing-impaired listeners. The aim is to
uncover the neural basis of pitch perception, using behavioral techniques
and, in collaboration with researchers at the Massachusetts Eye
and Ear Infirmary, functional magnetic resonance imaging (fMRI).
Selected publication:
Bernstein,
J. G., and Oxenham, A. J. (2003). "Pitch discrimination of
diotic and dichotic tone complexes: Harmonic resolvability or harmonic
number?," J. Acoust. Soc. Am. 113, 3323-3334.
Speech perception with acoustic and
electric hearing
Speech presented in isolation can be degraded and distorted in many
ways and still remain highly intelligible. Our work concentrates
on more critical situations, with the speech presented in various
acoustic backgrounds, where the auditory system has to “work
hard” render speech sounds intelligible. We use a so-called
noise-vocoder technique to simulate certain aspects of cochlear-implant
processing, with the aims of understanding normal speech coding
and improving cochlear-implant processing algorithms' ability to
deal with speech in challenging acoustic environments.
Selected publications:
Smith,
Z. M., Delgutte, B., and Oxenham, A. J. (2002). "Chimaeric
sounds reveal dichotomies in auditory perception," Nature 416,
87-90.
Qin, M. K.,
and Oxenham, A. J. (2003). "Effects of simulated cochlear-implant
processing on speech reception in fluctuating maskers,"
J. Acoust. Soc. Am. 114, 446-454.
Functional anatomy of auditory scene
analysis
We effortlessly parse an incoming acoustic waveform into perceptual
objects (such as words or notes) or streams (such as speech or melodies),
but very little is known about the underlying neural processing
beyond the level of the cochlea. This project aims to uncover neural
correlates of auditory object and stream formation by measuring
the changes in brain activation (using fMRI) that occur in various
acoustic situations where listeners hear one, two, or many auditory
streams.
Conference abstract:
Wilson, E.
C., Melcher, J. R., Micheyl, C., Oxenham, A. J. (2004). "Neural
correlates of auditory stream segregation in humans using fMRI,"
Assoc. Res. Otolaryngol., Feb. 2004, Daytona Beach, FL (abstract).
Our research is funded primarily by the National
Institute on Deafness and other Communication Disorders (NIDCD).
|