Ludo Max - US grants

Under the direction of Dr. Ludo Max, Ms. Margaret Earnest will collect data for her doctoral dissertation. Her research includes three studies investigating the control and coordination of lip and jaw movements in infants and children from 6 to 37 months of age. This work builds on increasing evidence that the transition from babbling to meaningful speech is a crucial stage during which motor constraints may determine important aspects of speech sound acquisition. One major question related to this transition is whether it reflects a maturation that is gradual and continuous or whether early speech requires an extensive reorganization of the previously acquired motor skills. Therefore, two of Ms. Earnest's studies will investigate developmental trends in (a) the respective contribution of individual articulators (lips and jaw) to bilabial closing and opening gestures, and (b) the typically asymmetric nature of these articulatory movements during speech production. Her third study will examine the potential neuromotor basis for infants' selection of the jaw as the primary articulator in babbling and early speech production. Each of these three questions will be addressed by recording movements of the lips and jaw with a camera-based movement tracking system and comparing a variety of kinematic parameters across different age groups.

This research on the early development of orofacial control for babbling and speech is significant for several reasons. First, it will lead to new insights into the neuromotor processes underlying speech development in children. Second, an enhanced understanding of the different stages of speech motor development may be critical for explaining commonly observed trends in the sequence of speech sound acquisition during babbling and early speech. Third, given this potential influence on the order of speech sound acquisition, the constraints imposed by developing speech motor abilities may affect other aspects of language development.

DESCRIPTION (provided by applicant): Understanding the basic neural mechanisms underlying stuttering is widely acknowledged as fundamental to informed diagnosis and treatment. The required cornerstone for this important knowledge is a theoretical framework of stuttering that accounts for various primary and associated speech characteristics and that is consistent with empirically-verified models of sensorimotor control and neural functioning. The research program proposed here takes a comprehensive neurobiological approach to explaining the neural basis of stuttering through an integrated series of theoretically-motivated, hypothesis-driven experiments. Parallel psychophysical (kinematics, sensorimotor adaptation, mechanical/sensory perturbations) and neuroimaging (fMRI) experiments will be conducted to address selected aspects of speech sensorimotor control that, according to our theoretical framework, may be implicated in stuttering. Specific aims of the series of experimental studies are to investigate in individuals who do vs. who do not stutter (a) the ability to acquire and consolidate neural representations (i.e., internal models) of the mappings between central motor commands to the vocal tract musculature and the sensory consequences of those actions, (b) the efficiency of integrating auditory and kinesthetic afferent signals into both the feedforward and feedback components of speech sensorimotor control, and (c) the activation time course and functional connectivity of the neural substrates underlying speech production. This is a collaborative program of research by scientists who have overlapping as well as complementary areas of expertise and who direct research groups using state-of-the-art instrumentation at two performance sites. Combining the expertise and resources from these sites will allow innovative investigations of the sensorimotor systems of stuttering and nonstuttering children and adults at behavioral, physiological, and neural levels of operation. These in-depth studies have the potential to inform on the development and state of the speech motor control system in individuals who stutter, and to suggest new directions for research and clinical management. Thus, this work's direct relevance to public health lies in its contributions to understanding the neural mechanisms underlying stuttering and-by generating such new insights-facilitating the development of improved approaches to diagnosis and treatment.

The Computer Resources Core (Core B) provides a spectrum of services to support and enhance the research endeavors of a core group of scientists investigating questions related to hearing, communication and balance at the University of Washington. The overall goal is to increase the productivity of our research through better use of computers. Specifically, we aim to: enable completely new types of research;accelerate development and spread of technologies new to the University of Washington;facilitate collaboration or interaction among users of the Core;help reduce redundant work by providing consolidated computer expertise accessible by all users of the core;maintain a high level of basic computer support for all supported research groups. We endeavor to provide computer expertise within a broad enough scientific context that any one solution would have potential for more than one application. In consultation with the members of the Core, the Computer Specialists supported by the Core will select a software package or develop custom software to fit the goals of the experiment or analysis desired. The Computer Specialists are responsible for testing and debugging software applications and training and assisting core users to apply the software in their research. Likewise, hardware solutions will be implemented in a similar manner. The Computer Specialists will also help to disseminate information about solutions to particular problems to other Core investigators who might be able to incorporate such solutions into their.own research.

? DESCRIPTION (provided by applicant): Sensorimotor learning plays a critical role in the acquisition and refining of all skilled movements, including speech production. From early babbling to fully mature speech articulation, the central nervous system acquires and updates neural representations of the intricate motor-to-auditory transformations that take place from the generation of motor commands to vocal tract movements and speech sound output. Moreover, auditory-motor learning - the process through which such neural representations are learned and maintained - is believed to play an important role in the etiology of developmental speech disorders such as stuttering and childhood apraxia of speech. This series of six integrated experiments therefore seeks to gain a better understanding of the principles and mechanisms involved in speech sensorimotor learning in general and in auditory-motor learning in particular. The overall program of research is designed around the dual short-term goals of (a) optimizing the rate and extent of auditory-motor adaptation, and (b) minimizing the rate and extent of de-adaptation (decay of sensorimotor learning). The findings from these studies will also elucidate the developmental progression of auditory-motor learning during childhood as well as differences in auditory-motor learning between children and adults. Furthermore, given that the core experimental paradigm for auditory-motor adaptation studies causes speakers to automatically alter their speech output in a short period of time, without instruction, and without effort, one long-term goal of the proposed research program is to develop novel, computer-assisted clinical procedures that induce adaptive changes in speech motor behavior by systematically altering the speaker's auditory feedback. Thus, this work's direct relevance to public health lies in the fact that the generated knowledge will contribute directly to an in-depth understanding of typical speech development, the maintenance of speech articulation skills throughout the lifespan, and fundamental sensorimotor mechanisms underlying developmental speech disorders, while simultaneously paving the way for highly innovative clinical techniques for the treatment of a wide variety of speech disorders.

PROJECT SUMMARY/ABSTRACT Understanding the basic neural mechanisms underlying stuttering is widely acknowledged as fundamental to informed diagnosis and treatment. The required cornerstone for this important knowledge is a theoretical framework of stuttering that accounts for various primary and associated speech characteristics, and that is consistent with empirically-verified models of sensorimotor control and neural functioning. The research program proposed here takes a comprehensive neurobiological approach to developing a mechanistic model of stuttered speech dysfluencies through an integrated series of theoretically-motivated, hypothesis-driven, state-of-the art experiments. A common theme throughout the proposed experiments is the fact that the neural control of movement depends on dynamically adjusted bidirectional interactions between efferent and afferent systems. The direct aim is to elucidate these sensorimotor interactions and their role in stuttered speech. Based on empirical and computational work suggesting that the CNS is able to control fast voluntary movements by continually predicting future sensory states, our lab recently found in multiple studies that typical speakers modulate auditory processing mechanisms prior to the initiation of speech movements, but that this mechanism is entirely lacking in adults who stutter. Thus, predictive modulatory mechanisms prove to be a particularly powerful model for elucidating the mechanisms underlying speech motor breakdowns in stuttering. The individual experiments within this program of research are designed to determine whether stuttering individuals? well-documented deficit in pre-speech auditory modulation is already present in childhood close to stuttering onset, whether this deficit is specific to motor-to-auditory interactions or also affects processing in the somatosensory domain, and to uncover various aspects of the phenomenon?s functional relevance in speech sensorimotor control. The proposed studies comparing both children and adults who stutter with typically fluent speakers have the potential to offer mechanistic insights into the development and limitations of the speech sensorimotor system in this common disorder of speech fluency. Specifically, crucial new insights will be gained into the involvement of sensorimotor interactions in feedback monitoring mechanisms that have long been hypothesized to play a fundamental role in the physiological basis of stuttering. Moreover, these findings will offer suggestions for novel treatment approaches such as non-invasive brain stimulation of neural pathways involved in pre-movement motor-to-sensory signaling. Thus, this work's direct relevance to public health lies in its contributions to understanding the neural mechanisms underlying stuttering and ? by generating such new insights ? facilitating the development of improved approaches to diagnosis and treatment.