Auditory Perception and Cognition Group :: Andrew J. Oxenham, PhD
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Our Research

 

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:

  1. 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.
  2. 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).

 

 
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