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Neuroscience Graduate Program at UCSF
Learning and Adaptation in Sensorimotor Control:
Human Psychophysics and Neurophysiology and Computational Methods
It has been known for over a century that the visuomotor transformations underlying reaching are highly adaptive. When optical prisms are placed over the eyes, for example, subjects quickly adapt to the displacement of visual feedback. This is shown by the fact that if the prisms are removed after even only a few movements, subjects exhibit reaching errors in the direction opposite the visual shift, despite the fact that their vision is now correct. Furthermore, the adaptive capabilities of the sensorimotor system are complex, e.g. displaying context dependent effects. Finally, sensorimotor learning is a continuous process: even in natural environments, sensory feedback from each behavior influences performance in subsequent movements. How sensorimotor learning takes place is a crucial question both for understanding the sensorimotor system and for developing more general theories of neural plasticity at the functional level. The mechanisms of sensorimotor adaptation are the primary focus of my lab. We address these issues with a combination of psychophysical, physiological, and computational methods.
Psychophysics of Sensorimotor Adaptation: We are using human psychophysical studies to gain an understanding of the computational principles underlying sensorimotor adaptation. With our virtual reality setup, we can artificially manipulate the visual feedback available to the subject while they perform arbitrary reaching tasks. Upcoming experiments will focus on adaptation in the face of alterations of the visuomotor map. While a simple prism-like shift of the visual world is easily learned, earlier experiments of mine have shown that human subjects are unable to adapt to more complex perturbations. By probing the limits of learnable maps and observing how the sensorimotor system generalizes to movements outside the training domain, it will be possible to identify the adaptive degrees of freedom.
Sensorimotor Learning in Development: We are preparing to investigate the development of visually guided behavior by studying children of various ages. One question of particular interest is whether there is a varying tradeoff during development between flexibility and robustness of behavior. This could be manifested, for example, by a progressive restriction in the degrees of freedom of the sensorimotor map with a concurrent increase in the ability of the system to generalize across the workspace.
Neural Basis of Sensorimotor Adaptation: The sensorimotor pathways responsible for visually guided reaching are an ideal system for studying the neural basis of adaptation. As discussed above, the transformation from vision to action can adapt quite rapidly. This allows us to monitor the fine temporal dynamics of cortical changes in relation to behavioral changes. In addition, the primary cortical pathways underlying reaching have already been identified. Of greatest interest here is the reciprocally connected network of sensory and motor areas which appear to be responsible for converting perception into action: the Superior Parietal Cortex (Areas 5, V6a, and MIP which combine visual and somatosensory information into the precursors of movement commands) and the Frontal motor areas (PMd and M1). Furthermore, rapid progress is being made in understanding the neural representations recorded in these areas. We are in the process of building a state-of-the-art physiology laboratory, including a 64-channel recording system. We will use this lab to study the role of the cortical sensorimotor network in sensorimotor adaptation.
Reach Planning: The central nervous system (CNS) has access to an overabundance of perceptual information and has control over a body with a vast number of independent degrees of freedom. For a given set of behaviors, what information does the CNS utilize from this perceptual flow, what aspects of the movement does it attempt to regulate, and what computational principles and physiological mechanisms underly the sensorimotor transformation? We are addressing these questions with a combination of computational and psychophysical methods. One key topic in this work is the way in which information from the various sensory modalities and from internal predictive models are combined.
Sam Sober, Graduate Student, B.S. Wesleyan University, Psychophysics of Adaptation and Motor Planning
Sam Sober's website: www.keck.ucsf.edu/~sam
Sen Cheng , Sloan Postdoctoral Fellow, Ph.D. Physics, Michigan State University, Theory and Psychophysics of Sensorimotor Adaptation
Jason Ku, MSTP Rotation Student, BS, Sensorimotor Adaptation in Patient Populations; Physiology of Adaptation
Sabes, P.N, Breznen, B., and Andersen, R.A. "The Parietal Representation of Object Based Saccades." In Preparation.
Breznen, B., Sabes, P.N, and Andersen, R.A. "Dynamics of the parietal activity during object-based saccades." In Preparation.
Sabes, P.N. "The Planning and Control of Reaching Movements." In Press, Current Opinions in Neurobiology (2000).
Sabes, P.N, Jordan, M.I., and Wolpert, D.M. "The role of inertial sensitivity in motor planning." J. Neuroscience, 18:5948-5957 (1998).
Sabes, P.N and Jordan, M.I., "Obstacle avoidance and a sensitivity model of motor planning." J. Neuroscience, 17:7119-7128 (1997).
Philip N. Sabes, Ph.D.
Phone
415-476-0364
Physical Address
513 Parnassus
HSE-816
Mailing Address
UCSF, 513 Parnassus Box 0444
San Francisco, CA 94143-0444
For Internal Campus Mail
Box 0444
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