John F. Soechting - US grants

The long term goals of this project are to arrive at a better understanding of how the central nervous system works to organize and control the limb movements involving more than one joint. The problems that arise in he organization and control of such movements concern questions such as: how is a point in space mapped into a proper set of joint angles so that the limb moves accurately to a target, how are the many muscles required to produced a movement coordinated, and what kind of feedback is appropriate to control multi-joint limb movements? This proposal deals with each of these problems. Psychophysical studies are planned to identify how information on the location of a point in extra-personal space and the orientation of the arm is represented within the central nervous system. Other experiments deal with the question: what are the rules which determine the proper level of activation of different muscles given a desired amount of torque. Results of these experiments should provide a better understanding of how the CNS normally controls movements and provide the basis for a better assessment of movement disorders and for the rational design of prosthetic devices.

Skilled movements are thought to be produced by adding together in series a number of simpler movements. In the case of skilled movements of the hands and fingers, simultaneous movements of both hands are often involved. This project to be conducted by Dr.John Soechting will use the movements of the hands and fingers during typing as a model for the way in which complex, bimanual movements can be derived by putting together a sequence of simpler movements. In typing, these simpler movements are the individual keystrokes and the movment sequence is the series of keystrokes that generate a word or a phrase. The motions of the hands and of the fingers will initially be described for single letters typed in isolation. Then the process of how such individual movements are put together in series will be studied by asking subjects to type words in which only two letters are typed by one hand and all other letters are typed with the other hand. Finally, by changing the location of the keys on the keyboard and forcing typists to relearn the keyboard layout, the processes by which movement sequences are learned will be studied. This research will contribute to understanding how individual motor acts are integrated to form coordinated series of movements.

DESCRIPTION: (provided by applicant) The overall aim is to determine how visual and kinesthetic sensory information is used online to guide movements. A better understanding of these processes is important for rehabilitation and the development of orthotic devices for patients with senson-motor deficits. There are two principle aims. One major aim is to provide a foundation for understanding the neural processes in tactile handling - the manipulation of tools. To this end, we will study the motions and forces developed by the fingers in grasping and manipulating objects, and the processes whereby kinesthetic information can be used to identify an object by its shape. The second major aim tests the hypothesis that gaze signals, of extraretinal origin, provide a major input to the limb motor control system. Visual guidance of grasping movements will be studied by comparing the kinematics of the hand and fingers when visual and or tactile information is unavailable with the behavior when this information is present. The temporal evolution of hand and finger kinematics will be characterized, as will be the times at which various sources of information become important. The guiding hypothesis of this study is that there exist a few temporal patterns of coordination (synergies) that account for most of the variations in finger kinematics. The control of grip forces in a tripod grasp will be studied under non-equilibrium conditions - for example, when the grasped object is rotated. Previous investigations restricted to static, equilibrium conditions had uncovered a simple synergy and the proposed investigations will determine how this synergy is modified under more general experimental conditions. The third part of the first aim will be to determine the extent to which kinesthetic information can be utilized to deduce hand trajectories, in particular, distortions in the kinesthetically derived information about curvature and rate of change of curvature of hand trajectories will be determined. The ultimate aim of this project is to define the algorithms whereby information about endpoint trajectories are derived from biological variables such as muscle lengths or joint angles. The hypothesis underlying the second aim is based on previous observations that errors in gaze induced by visual illusions are accompanied by errors in limb motor control in pointing or interception tasks. To test this hypothesis, ocular and manual tracking performance will be investigated in patients with spinocerebellar ataxia. Since the cerebellum is intricately involved in tracking, this task is a very sensitive test of cerebellar function and has been found to elicit errors in this patient population. The hypothesis predicts that errors in ocular and manual tracking should be reliably correlated in time and in amplitude.

DESCRIPTION (provided by applicant): The aims of this project are to identify the variables important for the control of eye and hand movements used to track visual targets moving in two dimensions. The proposal is based on the premise that studying movements in two or more dimensions reveals unexpected facets of neural control mechanisms. While considerable work has been done on reflexive and saccadic eye movements in three dimensions, multi-dimensional pursuit tracking is less well understood. Recent evidence suggests that there is much more interaction between the brain centers controlling eye and limb motion than previously thought, and this proposal also aims to further the understanding of these interactions in the context of tracking. The proposal has three specific aims. The first aim is to characterize qualitatively and quantitatively the response of the smooth pursuit system to step changes in target direction. Normally, ocular tracking involves saccades as well as smooth pursuit. For this aim, a paradigm has been developed to minimize the probability of intervening saccades. The second aim is to study interactions between ocular and manual tracking of a target. Experiments are proposed in which subjects will track targets moving in two dimensions, with the eye and/or the hand. The hypothesis to be tested is that a gaze signal provides an important input to the limb motor control system and that ocular tracking will be modified to accommodate limb control. Control experiments will test the effects of attention on the ocular response. The third aim is to generalize the results of the first two aims, with the goal of being able to predict normal eye and hand tracking of curvilinear motion. Studies proposed under this aim will determine whether the information used to control tracking is the same as that used for target interception, whether eye and hand tracking is under intermittent control, and whether information about curvature and rate of change of curvature of target motion is utilized in tracking. Control experiments will assess the influence of expectations on the response. The results of these experiments will be incorporated into a quantitative model. The results of this work will characterize normal human tracking behavior. As such they will provide a norm for diagnostic testing in patient populations. Furthermore, this work will identify the logical operations carried out by different brain areas in transforming a visual signal into motor commands to the eyes and to the limbs, and will consequently refine our understanding of brain function.