Neural Encoding Lab
- Eric D. Young, Ph.D., Professor of Biomedical Engineering
- Murray B. Sachs, Ph.D., Professor of Biomedical Engineering
- Bradford J. May, Ph.D., Professor of Otolaryngology-Head and Neck Surgery
- Paul Nelson, Ph.D., postdoctoral fellow
- Sean Slee, Ph.D., postdoctoral fellow
- Amanda Lauer, Ph.D., postdoctoral fellow
- Josh Vogelstein, graduate student
- Tessa Ropp, graduate student
- Matt Roos, graduate student
- William Tam, graduate student
- Ben Haeffele , graduate student
- Yang Li, graduate student
Research in the neural encoding laboratory investigates the representation and processing of complex stimuli in the auditory system. One goal is to understand the relationships between the perception of sound and the responses of auditory neurons. Another is to analyze the effects of hearing impairment on the representation and to investigate signal processing for neural prostheses. Some specific examples of our approach:
1. Neural circuits in the brainstem auditory system. How is the brain organized for auditory information processing? How are neurons interconnected and how do they interact? Examples of research in this area:
2. The representation of complex stimuli in neural responses. How does the activity of neurons in the brain represent the acoustic environment? How do we discriminate between sounds? How can we understand and model the neural representation of sound? Examples of research in this area:
- Receptive fields of auditory neurons can be linear or nonlinear - Auditory spectral receptive fields become nonlinear in some neurons in the cochlear nucleus. A method of constructing receptive fields for spectral shape (i.e. the frequency content of sounds) gives first and second-order receptive fields. These are used to show that neurons in the ventral cochlear nucleus are reasonably linear, i.e. well-represented by first plus second order models, whereas neurons in dorsal cochlear nucleus are frequently nonlinear.
- Receptive fields of auditory neurons can be linear or nonlinear - A method of constructing receptive fields for spectral shape (i.e. the frequency content of sounds) gives first and second-order receptive fields. These are used to show that neurons in the ventral cochlear nucleus are reasonably linear, i.e. well-represented by first plus second order models, whereas neurons in dorsal cochlear nucleus are frequently nonlinear. The nonlinearity in dorsal cochlear nucleus is mainly caused by the effects of sound level, possibly through the actions of inhibitory interneurons.
- Neurons in dorsal cochlear nucleus are more linear at low spectral contrast - The linearity of receptive fields depends on the degree of spectral contrast (meaning the fluctuation of sound levels in the sound spectrum). In addition, the gain of neurons increases at low contrasts. These effects occur in the auditory nerve, but are stronger in the dorsal cochlear nucleus.
- Information about sound localization is distributed across neuron types in the inferior colliculus - Three neuron type can be recognized in the inferior colliculus, based on response maps. These seem to be connected differently to brainstem auditory neurons, suggesting a difference in the representation of different sound localization cues. Analysis of the representations using mutual information shows that some segregation exists, but generally auditory information is distributed broadly across the response types. Information is also coded in temporal aspects of spiking, like first spike latency.
- Perceptual forward masking corresponds well to the properties of neurons in inferior colliculus - The dynamic range of perceptual forward masking is very wide, up to 80 dB, whereas in the auditory nerve, the dynamic range is 30 dB or less. The inferior colliculus seems to have inhibitory inputs that widen its dynamic range for masking to correspond to that seen psychophysically.
3. Studies of stimulus representation in animals with hearing impairment. Acoustic trauma is used to produce a hearing loss resembling a sloping high-frequency hearing loss, typical of older listeners and hearing-aid users. Examples of research in this area: