Esther Thelen - US grants

Support is requested for a program of research in the developmental origins of motor control in humans. The overall goal of the program is an understanding of aspects of the motivational, neural, and biomechanic contributions to the acquisition of motor competence during the first year. A new model is proposed which integrates current theoretical advances in motor control with a developomental and ecological perspective. The model is used to conceptualize research in three areas. The first study is a completion and replication of a longitudinal investigation of the electromyographic and kinematic characterictics of spontaneous infant kicking, a behavior I believe is an important precursor to mature locomotion. This descriptive project will report on the temporal and topographical changes in leg movements, and the patterns of their underlying muscle activations. A second study asks what happens to a spontaneous movement when it comes under voluntary conrol. These experimens will reinforce spontaneous leg kicks for frequency and/or topographical qualities to assess which parameters are stable and which amenable to voluntary control. The third group of experiments will manipulate themass of the legs through adding weights and having infants move underwater. These studies will assess the effect of mass changes on movement quality. Infant motor behavior is a neglected area of study in human development and this research is unique in approaching motor development from the perspective of current motor theory. It offers the promise of leading to a new synthetic theory of motor development, but it also is an essential precursor to similar studies directed to diagnosis and treatment of neuromuscular dysfunctions and to the motor consequences of developmental delays.

The overall goal is to understand the role of limb dynamics in the acquisition of motor skills in infancy. When limbs move in voluntary and involuntary actions, their trajectories are a result of active muscle contractions, the forces of gravity, and the motion-dependent forces that arise from the mechanical interactions of the segments of the limbs, the intersegmental dynamics. Neuroscientists have discovered that these nonmuscle forces can contribute significantly to the motion of limbs and that particular joints appear to be especially responsive to these motiondependent forces. There is strong evidence that harnessing and optimizing dynamics is essential to skill acquisition at all ages. Such biodynamics factors have never been quantified in infants. A systems-functionalist theoretical framework is used to generate questions about the development role of dynamical factors: 1. How are moments of force partitioned among the body segments in newborn infants? 2. What is the effect of posture? 3. How do limb dynamics change with age? 4. How do limb dynamics change with task? 5. What are the underlying patterns of muscle activities in common infant actions? 6. How do perturbations of movements affect limb dynamics? These questions will be answered by collaboration between the motor development laboratory of Thelen and the biomechanical laboratory of Zernicke. Infants in a longitudinal and several cross-sectional studies will have their movements recorded by a computerized motion-analysis system, and kinematic and kinetic measures of limb coordination, control, and distribution of energy will be determined. These studies have important developmental implications: 1. They describe, for the first time, how forces are apportioned among body segments as infants gain skill. 2. They show how dynamical factors interact with other structural and contextual variables to determine motor performance. 3. They provide a principled basis for understanding how information about the individual's body and the external world can be transduced to produce developmental change.

I have three broad goals for the period of requested support. The first is to continue work on a general theory of development based on dynamic systems principles. The theory seeks to describe, and hopefully, to model, developing organisms as multicomponent systems, where the elements of the system are coupled in parallel, and where the resulting behavior obeys the general principles of nonlinear dynamics. Plans for professional growth include tutorial and collaboration with scientists working on dynamic and connectionist models in motor control and cognition. The second goal is a program of research devoted to understanding an aspect of skill development in infancy. This research, in collaboration with a leading biomechanist, Dr. Ronald F. Zernicke, of UCLA, seeks to understand how infants harness and optimize the forces associated with moving their limbs and body segments, a process believed to be essential in acquiring skill. A systems- functionalist theoretical framework is used to generate questions about the development role of these so-called intersegmental dynamics. 1. How are the moments of force partitioned among the body segments in newborn infants? 2. How do limb dynamics change with and affect, task? 3. How do limb dynamics change with age? 4. What is the effect of posture on skill acquisition? 5. What are the underlying patterns of muscle activities in common infant actions? 6. How do perturbations of movement affect limb dynamics? Infants in a longitudinal and several cross-sectional studies will have their movements recorded by a computerized motion-analysis system, and kinematic and kinetic measures of limb coordination, control, and distribution of energy will be determined. These studies have important implications for understanding skill development: 1. They describe, for the first time, how forces are apportioned among body segments as infants gain skill 2. They show how dynamical factors interact with other neural, structural, and contextual variables to determine skill performance. 3. They provide a principled basis for understanding how information about the individual's body and the external world can be transduced by the nervous system to produce action, and ultimately, developmental change. My final goal is to write the theoretical and empirical work in a monograph.

workshop; information theory; information system analysis; child physical development; child psychology; travel;

Funds are requested for an ADAMHA Research Scientist Award to support research in the acquisition of skills in infants. There is an intimate relation between developing perceptual-motor skills and all other areas of mental functioning during early life. The proposed studies are informed by a dynamic systems perspective. Thus, the research strategy is twofold: (1) to provide a detailed description of the developmental changes in reaching and walking and their multiple interacting subsystems, and (2) to identify and experimentally manipulate agents and processes critical to the emergence of new behavioral forms. Specific aim 1 is to complete the analysis of longitudinal data on the kinematics, kinetics, and muscle patterns of infant reaching, collected weekly from 4 infants from weeks 3-52. This will describe the transition from spontaneous to goal-directed reaching, the improvements in the accuracy, speed and smoothness in reaching, and the dynamic segmental forces and muscle patterns that underlie these changes. Specific aim 2 is to conduct a longitudinal study of infants between 6 months and 18 months to trace the kinematic, kinetic and EMG characteristics of treadmill steps, supported steps, and independent walking. This study will describe the developmental transition in the neuromuscular precursors of walking when infants stand, bear weight, and move forward independently. Specific aim 3 is to conduct experiments where kicking and reaching movements are perturbed by a slight tug, which simulates the naturally occurring internal and external force environment. This study investigates how infants detect and adjust their muscles to proprioceptive input. Specific aim 4 is a series of experiments investigating how infants acquire new motor forms. Infants will be trained to use bilateral kicks to activate a mobile, and the conditions and contexts that facilitate learning and remembering the new pattern of coordination will be manipulated. These studies are important to (1) illuminate basic developmental processes; (2) understand fundamental mechanisms of perceptual-motor coordination and control; and (3) impact on clinical practice.

The goal of this research program is to understand the acquisition of motor skills in infancy and early childhood. Specifically, this research is concerned with the dual-nature of skill: how children learn to become both stable in their performance and flexible in their abilities to engage in new tasks. The studies are informed by a dynamic systems perspective and address skill development in terms of dynamics tested and coupled over levels and time scales. This theoretical approach focuses on the multiple, interacting factors that lead to movement. Here we especially consider how perception, motor memory, and task intersect in producing movements of eyes and head, and manual actions of varying complexities. Studies look at changes in real and developmental time and include empirical research, model simulation and robotics. Specific Aim 1 is based on a new model of infant visual habituation. In six experiments, we manipulate the metric parameters contributing to infants' development of visual attention. In Specific Aim 2 we study the dynamics of action memories for simple reaching with hands and with feed in infants and toddlers, and how those memories interact with visual attention. Specific Aim 3 is to study the dynamics of complex motor actions. Infants and toddlers are tested with toys of varying complexity to understand how recent and longer-term experience affect their tendencies to repeat or switch to new actions. In Specific Aim 4 we implement these theoretical models in an autonomous robot to further explore mechanisms of real time behavior and its developmental course. Specific Aim 5 is to continue experiments on infant limb perturbations currently funded and Specific Aim 6 to write a book on development of embodied cognition based on these and previous experimental and modeling work. These studies impact upon our understanding of basic mechanisms of skill development and continue to contribute new theories of clinical intervention in pediatric physical and occupational therapy.