Future Research Goals
A. Psychophysical investigation of outcome differences in speech motor learning
Variability in speech is ubiquitous, yet little is known about the sources of variability, their importance and their neural underpinnings. Sources of variability in speech can be sensory, motor or both and by studying the variability patterns the sensorimotor support mechanisms of speech can be unraveled. A knowledge of variability will further aid in our understanding of motor control issues in speech disorders as evidenced by the emergence of characteristic variability patterns in disordered speech. Until now, there is little research done linking the fundamental sources of variability in speech with the patterns of speech motor control. One of our long-term research goals is to study the origins and structures of variability in speech, their neural foundations and relationship to speech motor control and apply the knowledge gained to understand speech development, age related changes to speech and disorders of motor speech such as stuttering, apraxia and dysarthria.
We expect that there are variability phenotypes in speech, that is, the characteristic variability patterns inherently present in an individual’s speech, and that they can be globally partitioned into sensory and motor variants. The variability phenotypes would capture the sensory and motor supports in speech and show how they vary across the individuals, affected by healthy development or speech disorders.
B. Neural underpinnings
Determining the neural substrates that underlie sensorimotor processes in speech is important for understanding the brain basis for speech motor behaviors and may have clinical implications. One of our goals is to understand the neural basis of the sensorimotor functions outlined above using EEG. we are investigating the neural dynamics of speech motor learning by using the methods of phase synchrony that presumably illuminates the process of information transfer across neuronal populations. The use of neural phase coherence (synchrony) has proven to be successful in elucidating spatio-temporal dynamics of learning and memory and explicitly looks into the time locking between the phases of two oscillations. Essentially, synchrony quantifies the dynamics of coordinated activity across neuronal populations that comprise functional networks, including speech motor control, on a -1.0 – 1.0 scale. Very little is presently known about the brain dynamics of motor speech development and the emerging patterns of neural synchrony in the context of speech motor learning.
Our approach compliments the more recent progress based on the fMRI neuroimaging techniques in documenting the brain structures and their connectivity patterns that support sensorimotor learning in speech. The fMRI studies provide little insight into the underlying neural dynamics due to the well-known limitation of the fMRI techniques in resolving temporal details. Indeed, a complete understanding of the neural processes that underlie speech would require complementary knowledge of the functional networks of the brain structures involved and of the neural dynamics that these networks support. Methods of neural synchrony have the potential to break new grounds in understanding the neural mechanisms of speech production/perception.
C. Orosensory contributions to dysphagia
Our interest in dysphagia followed recent exciting developments in human motor control in which there is growing realization on the close link between action and perception. In speech also, perception and production are increasingly found to be tightly integrated. By contrast, little research has been done that examines the relationship between swallow motor function and oral sensation, although we suspect a strong relationship between the two. We started pursuing this research objective with late Dr. Jeri Logemann at Northwestern University that has evolved in a full-fledged research endeavor in collaboration with Dr. Barbara Pauloski at University of Wisconsin at Milwaukee.