Auditory Biophysics and Simulation Laboratory
Department of Biomedical Engineering
44 Cummington Street, Boston, MA 02215
Principal Investigators: David C. Mountain, Allyn E. Hubbard
The goal of this project is to bridge the gap between basic research in cochlear physiology and clinical tools in otology such as otoacoustic emissions and cochlear implants. We are using a combination of experimental and theoretical techniques to develop comprehensive computer models of cochlear function. The experimental work is specifically designed to generate detailed data sets that can be used for model parameter estimation and model validation. Our project specifically focuses on how the electrical and mechanical properties of the cochlea, both active and passive, result in the extremely sensitive responses observed in inner hair cells (IHC) and auditory-nerve (AN) fibers. The models being developed will be used to integrate a wide range of experimental data as well as to simulate changes in otoacoustic emissions due to cochlear pathology and to simulate the electric fields produced by cochlear implants.
We are addressing four fundamental questions:
- How does the architecture of the organ of Corti determine the passive mechanical properties of the cochlea?
- How do outer hair cell (OHC) electromechanical properties lead to cochlear amplification?
- What are the mechanisms that drive and distribute ionic current flow throughout the cochlea?
- Where and how are otoacoustic emissions produced in the cochlea?
To answer these questions, we are using a combination of experimental and theoretical techniques to study the mechanical and electrical properties of the gerbil and the human cochlea. We are developing detailed finite element hydromechanical and electroanatomical models of the cochlea, as well as an integrated finite difference model for the cochlear amplifier that incorporates both the hydromechanical properties and the electroanatomical properties of the cochlea. These models will allow us to simulate the intrinsic current flows that lead to clinically important field potentials such as the cochlear microphonic (CM), summating potential (SP) and the compound action potential (CAP), as well as to create tools that can be used to predict the effects of artificial currents such as those produced by cochlear implants. The models being developed can also be used to interpret emission data from normal and diseased ears.
At present, there are broad scientific and public concerns about potential impacts of human sound sources in the oceans. It is imperative for conservation purposes that a method be developed to assess how marine mammals may be affected by anthropogenic noise in the oceans. To achieve the necessary level of detailed insight known about hearing in land mammals would require acute experimentation on whales that is impossible for practical, regulatory, and ethical considerations. Therefore, we are developing alternative methods for obtaining reliable underwater hearing and impact estimates.
The overall goal of this project is to improve our understanding of how acoustic power is coupled to the inner ear of cetaceans in order to better predict the normal hearing capabilities of these species as well as to better predict the impact of man-made sounds.
The specific objectives of this project are to develop biophysically based models of the acoustic power flow from the water, through the tissues of the head and middle ear, into the cochlea, and ultimately to the sensory receptor cells (hair cells). These models allow us to estimate audiograms for multiple cetacean species from anatomical and mechanical measurements and to predict the excitation pattern within individual cochlea for a range of acoustic inputs as well as modeling stresses and strains on key cochlear tissues from over-stimulation.
Concerns about man-made sounds in the marine environment have been increasing over the last decade. The ONR Effects of Sound on the Marine Environment (ESME) team has been developing sophisticated tools for modeling and conceptualizing how sound propagates and interacts with marine life. The purpose of these tools is to estimate the impact of sound on the marine environment using state-of-the-art propagation and animal behavior models. The ESME Workbench software has the important distinction of being open source and peer-reviewed which allows the research community as well as the Navy to be completely aware of the details behind the simulations. In addition, the user interface for these tools is being carefully designed for ease-of-use for the non-expert without sacrificing the capability to model complex scenarios.
The ESME Workbench is the result of an ONR collaborative basic research initiative (Effects of Sound in the Marine Environment) aimed at simulating the propagation of sound through the ocean and its effect on the physiological function and behavior of marine organisms, with a focus on endangered and protected species. The goal of the ESME research program is to create novel modeling and simulation tools to aid in understanding the potential environmental impacts of manmade underwater sound in general and more specifically the impacts of Naval training exercises. The Workbench combines models of sound sources and propagation with biological models developed by basic research scientists at multiple laboratories into a single framework.
The long-range goal of the EarLab project is to create realistic, large-scale models capable of describing known physiology and capable of predicting human auditory responses to a wide range of acoustic stimuli or environmental insults. Applications range from improved design of cochlear implants to explaining how humans are able to function in complex acoustic environments. To achieve our goal we are synthesizing and integrating existing information on mammalian hearing and create software models and tools that will facilitate effective interaction between investigators from different research disciplines. The models and associated databases will improve our ability to take the knowledge obtained from animal experiments and apply it to humans. In the process of constructing and integrating the EarLab models and tools, data gaps will be identified that will need to be filled by future animal and/or human studies.
The informatics goals are to:
- create the computational infrastructure for a distributed modeling environment
- create desktop and web-based interfaces that will allow rapid reconfiguration of simulations and interchange of model modules
- develop databases and database tools to provide access to reference information useful for both experimental and simulation design and interpretation
- disseminate and support the software that we develop
The neuroscience objectives are to:
- apply EarLab models to studies of sound-source localization
- apply EarLab models to studies of auditory pattern recognition
- develop integrated models of cochlear implant function that can be used to study the factors that influence implant patients’ ability to localize and recognize sounds
Acoustic Mobility Aids
A small number of blind individuals have learned how to use echolocation to avoid obstacles and to identify objects in their environment. Unfortunately, most visually impaired people do not acquire this skill. The Auditory Biophysics and Simulation Laboratory is working to develop a sonar system that can be used as a mobility aid by those visually impaired individuals who can not echolocate on their own.
A pulsed ultrasonic source creates a beam of sound which is reflected back to the user from nearby objects. The returning echoes are shifted down to the audible frequency range and presented to the user via open canal earphones. The system can be mounted either on a baseball cap or on eyeglass frames so that the system will always be aligned with the user's head.