We study many aspects of hearing, ranging from how the ear processes sound to how the brain interprets the signals it receives from the ear. Most of our work involves behavioral (or psychoacoustic) studies using people with normal or impaired hearing. Here are some of the projects that people in our lab are currently working on:

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.

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 others, functional magnetic resonance imaging (fMRI) and magneto-encephalography (MEG).

Selected publications:

1. Bernstein, J. G., and Oxenham, A. J. (2003). "Pitch discrimination of diotic and dichotic tone complexes: Harmonic resolvability or harmonic number?," Journal of Acoustical Society of America, 113, 3323-3334.
2. Oxenham, A. J., Bernstein, J. G. W., and Penagos, H. (2004). "Correct tonotopic representation is necessary for complex pitch perception," Proceedings of the National Academy of Sciences USA, 101, 1421-1425. (See also commentary: Shamma, S. A. 2004. PNAS 101:11145.)
3. Penagos, H., Melcher, J. R., and Oxenham, A. J. (2004). "A neural representation of pitch salience in non-primary human auditory cortex revealed with fMRI," Journal of Neuroscience, 24, 6810-6815.

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:

1. Smith, Z. M., Delgutte, B., and Oxenham, A. J. (2002). "Chimaeric sounds reveal dichotomies in auditory perception," Nature, 416, 87-90.
2. Qin, M. K., and Oxenham, A. J. (2003). "Effects of simulated cochlear-implant processing on speech reception in fluctuating maskers," Journal of Acoustical Society of America, 114, 446-454.
3. Qin, M. K., and Oxenham, A. J. (2005). "Effects of envelope-vocoder processing on F0 discrimination and concurrent-vowel identification" Ear and Hearing, 26, 451-460.

Neural Bases 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 combining behavioral (psychoacoustic) measures with measures of brain activation (using MEG and fMRI) in various acoustic situations where listeners hear one, two, or many auditory streams.

Selected Publications:

1. Gutschalk, A., Micheyl, C. Melcher, J. R., Rupp, A., Scherg, M., and Oxenham, A. J. (2005). "Neuromagnetic correlates of streaming in human auditory cortex," Journal of Neuroscience, 25, 5382-5388.
2. Wilson E. C., Melcher J. R., Micheyl C., Gutschalk A., and Oxenham A. J. (2007). "Cortical fMRI activation to sequences of tones alternating in frequency: Relationship to perceived rate and streaming," Journal of Neurophysiology, 97, 2230-2238 .