Spatial and temporal modulation of joint stiffness during multijoint movement.

Joint stiffness measurements during small transient perturbations have suggested that stiffness during movement is different from that observed during posture. These observations are problematic for theories like the classical equilibrium point hypothesis, which suggest that desired trajectories during movement are enforced by joint stiffness. We measured arm impedances during large, slow perturbations to obtain detailed information about the spatial and temporal modulation of stiffness and viscosity during movement. While our measurements of stiffness magnitudes during movement generally agreed with the results of measurements using fast perturbations, they revealed that joint stiffness undergoes stereotyped changes in magnitude and aspect ratio which depend on the direction of movement and show a strong dependence on joint angles. Movement simulations using measured parameters show that the measured modulation of impedance acts as an energy conserving force field to constrain movement. This mechanism allows for a computationally simplified account of the execution of multijoint movement. While our measurements do not rule out a role for afferent feedback in force generation, the observed stereotyped restoring forces can allow a dramatic relaxation of the accuracy requirements for forces generated by other control mechanisms, such as inverse dynamical models.

Quantitative kinematics of gait patterns during the recovery period after stroke.

BACKGROUND AND PURPOSE: The purpose of this study was to assess the potential of a new quantitative kinematic analysis for the documentation and evaluation of recovery of gait function after neurological injury. METHODS: We assessed the kinematics of gait function in 16 patients with hemiplegia at varying intervals over a 1-year period after a stroke, using a novel method for gait pattern assessment based on principal component analysis. Conventional measures such as gait speed and stride length were also evaluated. Testing started as soon as patients became ambulatory after stroke. RESULTS: Of the 16 patients assessed, 7 showed at least a 50% increase in self-selected gait speed from the first to the last test. The results of the pattern analysis closely mirrred self-selected gait speed at higher speeds, but relative rankings derived from gait speed and the pattern analysis did not match for 6 of the 16 patients. Kinematic pattern analysis suggested that different mechanisms were used to generate changes in gait speed at different speed levels. CONCLUSION: There is a sizable fraction of the stroke population for whom kinematic gait pattern analysis can provide information that is different from that provided by speed, stride length, and cadence. The kinematic analysis can potentially provide information about the mechanisms of pathological gait.

Quantitative analysis of human movement synergies: constructive pattern analysis for gait.

To record three-dimensional coordinates of the joints from normal human subjects during locomotion, we used a digital motion analysis system (ELITE). Recordings were obtained under several different conditions, which included normal walking and stepping over obstacles. Principal component analysis was used to analyze coordinate data after conversion of the data to segmental angles. This technique gave a stable summary of the redundancy in gait kinematic data in the form of reduced variables (principal components). By modeling the shapes of the phase plots of reduced variables (distortion analysis) and using a limited number of model parameters, good resolution was obtained between subtly different conditions. Hence, it was possible to accurately resolve small distributed changes in gait patterns within subjects. These methods seem particularly suited to longitudinal studies in which relevant movement features are not known a priori. Assumptions and neurophysiological applications are discussed.

Lateral eye-movements, hypnotic susceptibility and imaginal ability in right-handers.

A total of 46 male and 36 female right-handers were assessed on three measures of left-moving, as well as on hypnotic susceptibility, and several measures of imaginal ability. The three left-moving indices intercorrelated significantly. However, none of these indices correlated significantly with hypnotic susceptibility or imaginal ability variables in either sex.

Effects of hypnotists' and subjects' sex on hypnotic susceptibility.

2 male and 2 female student-hypnotists administered the Stanford Hypnotic Susceptibility Scale, Form C to 49 male and 42 female subjects. Subjects were also administered a group hypnotic-susceptibility scale and questionnaire measure of absorption and willingness to cooperate with hypnosis. The effects of these three measures on Stanford, Form C scores were statistically controlled with analysis of covariance. Neither hypnotists' sex, subjects' sex, nor the interaction of these variables was significantly related to scores on the Stanford scale. Implications for hypnosis research were briefly discussed.