Onset of dyskinesia and changes in postural task performance during the course of neuroleptic withdrawal.

The effect of neuroleptic withdrawal on postural task performance of 20 adults with mental retardation was examined. Dyskinesia was measured using the DISCUS rating scale and postural stability using a force platform during a prospective longitudinal neuroleptic medication withdrawal protocol. Assessments were conducted at baseline and monthly intervals, extending to approximately one year following complete medication withdrawal, when significant changes in amount of postural motion and sequential pattern of postural movement complexity were observed.

Further evidence on the dynamics of self-injurious behaviors: impact forces and limb motions.

The dynamics of self-injurious behaviors (SIBs) were examined in 8 adults with mental retardation. The trajectories of the arm movements and the impact forces of the head blows were determined from a dynamic analysis of videotapes of discrete bouts of self-injury. The results revealed a high degree of cycle-to-cycle consistency in the qualitative dynamics of the limb motions, indicating that the motions involved in SIB are often stereotyped in nature.

Changing complexity in human behavior and physiology through aging and disease.

Lipsitz and Goldberger proposed that there is a loss in the complexity of physiological and behavioral systems with aging and disease. Here, we show that this unidirectional view of the change in system complexity is too narrow in its consideration of the actual changes that occur with aging and disease. An increase or decrease in the complexity of a behavioral or physiological system output can occur and the direction of change is dependent on the confluence of constraints that channel the system dynamics.

Impulse and Movement Space-Time Variability.

In 3 experiments, the authors examined movement space-time variability as a function of the force-time properties of the initial impulse in a movement timing task. In the range of motion and movement time task conditions, peak force, initial rate of force, and force duration were manipulated either independently or in combination across a range of parameter values. The findings showed that (a) impulse variability is predicted well by the elaboration of the isometric force variability scaling functions of L.

Coordination Patterns in Ball Bouncing as a Function of Skill.

By observing the coordination patterns of people of different ages and skill levels bouncing a ball, the authors addressed hypotheses regarding (a) the relative increase and decrease of degrees of freedom with learning and (b) the order of progression in the changing organization of those degrees of freedom with development and learning. The movement patterns of the dominant arm and hand of subjects at various skill levels were contrasted in a cross-sectional design so that the way movement organization changes as a function of practice could be examined. Nine subjects aged between 4 and 22 years bounced a basketball at a preferred rhythm while standing still.