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Kresge Hearing Research Institute

Department of Otolaryngology

Central Systems Laboratory

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Cortical Representation of Auditory Space

NIH-RO1-DC00420; P.I.: J.C. Middlebrooks
The specific aims of this project are to:

  1. evaluate the task dependence of cortical spatial sensitivity;
  2. identify cortical substrates of spatial release from masking;
  3. identify cortical substrates of spatial stream segregation.

Spatial hearing is essential for effective listening in a complex auditory scene. In the familiar “cocktail party problem”, a listener must localize a particular talker, must exploit that location information to reduce masking by sounds at other locations, and must be able to assign multiple sequential streams of sounds to discrete sources. We are exploring the cortical mechanisms of spatial hearing using psychophysical experiments in humans and cats and cortical physiology in cats. In the human psychophysics, we aim to quantify the perceptual algorithms by which listeners localize sounds and isolate sounds of interest from complex auditory scenes. In animal studies, we aim to identify cortical mechanisms that could underlie those algorithms. Ongoing studies in cats have demonstrated that the spatial sensitivity of cortical neurons tends to sharpen when the animal performs a localization task. We are beginning studies in which we will explore cortical mechanisms aspects of spatial release from masking and spatial stream segregation, again monitoring the effect of an animal’s task performance on cortical responses.

Cortical and Behavioral Responses to Cochlear Implants

NIH-RO1-DC04312; P.I.: J.C. Middlebrooks

The objective of this study is to evaluate auditory-cortical responses to stimulation of a cochlear prosthesis with the goal of designing stimulation strategies that optimize information transmission from the cochlear implant to the auditory cortex. In parallel, we exploit the cochlear implant as a research tool to explore basic mechanisms of central auditory function. Physiological experiments are conducted in anesthetized guinea pigs. Parallel psychophysical experiments in guinea pigs and humans are being carried out by co-investigator Dr. Bryan Pfingst.

The specific aims of this project are to:

  1. characterize the cortical transformation of codes for amplitude modulation
  2. distinguish peripheral and central mechanisms of temporal acuity and identify electric-stimulation parameters that influence forward masking
  3. quantify plasticity in transmission of temporal information resulting from deafening and chronic stimulation

Feasibility of an Intraneural Auditory Prosthesis Stimulating Electrode Array

NIH-NO1-DC-5-0005; P.I.: J.C. Middlebrooks

The objective of this study is to test the feasibility of direct stimulation of the auditory nerve as a new mode of auditory prosthesis. Experiments are conducted in anesthetized cats. We implant a 16-electrode stimulating array in the auditory nerve and record responses in the inferior colliculus. Compared to a conventional cochlear implant, the intra-neural electrode array offers advantages of more spatially restricted activation of auditory nerve populations and reduced interference among stimulated channels.