As you would expect from a program with such diverse expertise, SHBT has produced breakthroughs in fields from bioinformatics to biomedical imaging, from molecular biology to regenerative medicine. Some highlights:
Dr. Jennifer Melcher and her colleagues at the Martinos Imaging Center are developing a new technique for identifying areas of the brain with different structural properties, using fMRI. This method is the only approach that can be used to non-invasively map the features of the living brain which vary from person to person.
A team of scientists led by Dr. Dan Merfeld is developing a vestibular prosthesis, the first of its kind, restoring the ability to maintain balance for those who have lost this sense due to inner ear disease. The team was awarded a prize by the 2005 MIT Entrepreneurship Competition to commercialize this technology.
Dr. Frank Guenther and colleages at Boston University are developing DIVA, a neural network model of the brain processes underlying speech production and perception. In computer simulations, DIVA learns to control the movements of a virtual vocal tract in order to produce speech sounds. The model accounts for a large number of speech production phenomena, and can be used to help determine the neural bases of various communication disorders.
Dr. Christopher Shera is using mathematical models to understand how the inner ear processes, amplifies, and creates sounds. His research has revolutionized understanding of these processes in the field of cochlear mechanics - one of his findings demonstrates that the cochlea acts as a biological analogue of a laser oscillator. Clinical application of this research is leading to better noninvasive tests of infant hearing.
Dr. Stefan Heller and colleagues discovered the presence of stem cells in the adult inner ear. They demonstrated that these cells have the ability to differentiate into specialized sensory cells and neurons, which, together, convert acoustic energy into neural activity that is relayed to the brain. The discovery of these adult stem cells provides a source of cells for ongoing transplantation experiments that will help develop technology to rebuild a damaged ear.
Dr. Bertrand Delgutte and co-workers discovered that the envelope of speech signals is most important for conveying word meaning, while the fine structure is important for pitch and sound localization. To do this research they devised 'chimeric' sounds, which combine features of two different speech sounds into one. This finding may indicate that our brains process the meaning of sounds separately from their locations in space. It also has direct relevance for improving cochlear implant technology.
Humans can hear sounds that move the eardrum less than the size of a hydrogen atom. Using transgenic mice, a multi-university research team co-led by Dr. Charles Liberman demonstrated that prestin, a newly identified protein, is the molecular motor responsible for the thousand-fold amplification of sound-induced vibrations by the sensory cells in the inner ear. This result was a important step in piecing together the molecular mechanisms underlying the remarkable sensitivity of hearing.
A cross-institutional research team led by Dr. Steven Zeitels and Dr. Robert Langer is developing bio-implants to restore elasticity in vocal cords damaged by scarring, the leading cause of voice disorders. Major progress has been made in determining which biochemical constituents of the vocal cords need to be synthesized for an implant, and experiments are ongoing to assess the effectiveness of candidate substances.
Dr. Robert Hillman has been leading a research team that is developing an improved voice prosthesis to benefit the thousands of individuals worldwide who have lost the ability to produce voice and speech due to severe laryngeal dysfunction or surgical removal. The project has many innovative elements, including the construction of new sound sources, development of signal processing approaches, and precise hands-free pitch control via electromyographic signals to produce a more natural-sounding voice.
Dr. Donald Eddington performed a key role in a cross-institutional team to develop a new speech processing strategy for cochlear implants. This strategy led to significant improvement in speech reception for implant users and has been widely applied in the industry ever since.
By examining the relations between adjustments of articulatory parameters and the properties of the sounds that result from these movements, Professor Kenneth Stevens and his colleagues have shown that human speech production system is characterized by an inventory of quantal states. These states are a consequence of the physical structure of the system and its acoustic and aerodynamic attributes. The states coincide with the inventory of distinctive features that are used by linguists to describe phonological contrasts that occur across languages. The theory also proposes that for each feature, additional attributes are superimposed on the defining acoustic attribute to enhance its perceptual saliency.
A team of scientists led by Dr. Robert Weisskoff developed a revolutionary approach to functional magnetic resonance imaging (fMRI) that for the first time enabled the detection of sound-induced neural responses in the brain stem. Up until that time, fMRI had been mostly restricted to the study of activation on the cortex. This approach is now allowing scientists to learn more about small structures of the brain deep beneath the cortex.
Hearing research has long been at the forefront of neuroscience, particularly at its interface with technology. Auditory neuroscientists were the first to use computers in neurophysiology (1959), to use glass microelectrodes to record from single neurons (1943), to use digital technology for stimulus synthesis (1959), to use correlation techniques for neural system identification (1963), and to propose a neural architecture that performs a specific computation (1951). Many of these firsts occurred at Harvard and MIT.
Dr. Dennis Freeman and colleagues developed a laser-optical system for measuring sound-induced motions in the inner ear. The exquisite sensitivity of the cochlea to submolecular motions necessitated a system with unprecedented accuracy; this system is now being used in microlithography with the goal of manufacturing the next generation of computer chips.
