Factors Influencing Microstructure of Aiming Movements

Arizona State University, Scottsdale AZ

Investigators

Abstract

Movements of daily living, such as reaching for a glass of water or pushing an elevator button, are motor acts that most of us perform easily and without conscious consideration of how they are executed. However, it takes considerable time for children to learn to reach and aim accurately for objects. Also, these movements, which seem to be so easy for young and healthy individuals, can become difficult for older adults and patients with motor disorders. This suggests that the organization of aiming movements is not a simple task for the central nervous system. One of the observations that supports this assumption is that the final stage of aiming movements when performed by elderly individuals and Parkinson's patients usually includes "submovements" represented by a number of small inflections in movement profile that are hardly noticeable in movements of young adults. These submovements have always been interpreted as corrections performed to achieve required accuracy at the target. This research is based on the hypothesis that another factor, which emerges from mechanical properties of the arm, might also contribute to the submovement phenomenon. In this view, to terminate hand motion at the target, energy developed for movement production has to be dissipated, and this might require a specific control strategy that causes submovements. To investigate the role of this factor, the structure of aiming movements that require termination at the target will be compared to the structure of continuous point-to-point movements. The continuous movements will be from the initial point to the target and back to the initial point, and therefore they will not require termination of motion at the target. The effect of the motion termination factor will be enhanced by using a solid target that helps to terminate motion passively and a flexible target that requires active termination of motion. The study will be useful both for understanding basic principles of human movement control and for investigation of factors underlying dysfunction caused by age and motor disorders.