Manual asymmetries in goal-directed movement: examination of the motor output hypothesis

Control of the dominant and nondominant hand: exploitation and taming of nonmuscular forces

Movements of the dominant and nondominant hand have been claimed to differ with respect to how they take intersegmental dynamics into account. Consistent with this claim, movements of the dominant hand are hypothesized to better exploit the intrinsic limb dynamics, whereas movements of the nondominant hand are controlled to make the intrinsic dynamics ineffective as far as this is possible. For rapid finger oscillations this hypothesis implies a higher level of co-contractions in the nondominant than in the dominant hand. Replicating previous findings on finger tapping, finger oscillations of the dominant hand were faster and less variable than those of the nondominant hand. More importantly, the variance of the relative difference between myoelectric signals of antagonistic muscles and thus the power of reciprocal myoelectric activity was smaller in the nondominant hand, indicating a relatively higher level of co-contractions than in the dominant hand. In addition, a spectral decomposition of the total power of the relative-difference signal revealed stronger relative power in the frequency band of the finger oscillations in the dominant than in the nondominant hand. These findings are consistent with the hypothesis that for the dominant hand more accurate feedforward control is possible based on a more accurate internal model of limb dynamics.

Modeling variability of force during isometric contractions of the quadriceps femoris

The authors modeled variability of force during continuous isometric contractions of the quadriceps femoris. Twenty adults (aged 25 +/- 6 years old) performed isometric leg extensions. Target forces were 11 percentages of maximum voluntary contraction (%MVC), ranging from 2 to 95%, and 5 absolute levels, from 25 to 225 N. The authors used standard deviation of absolute force, coefficient of variation, and signal-to-noise ratio as measures of variability. The results suggested a nonlinear relationship between variability and level of force, which could best be expressed as %MVC and not as absolute force. Variability for continuous isometric contractions was described best by a sigmoidal logistic function. The sigmoidal pattern of variability as a function of %MVC is consistent with physiological mechanisms.

Goal-Directed Aiming: Correcting a Force-Specification Error With the Right and Left Hands

In 2 experiments, the authors examined manual aiming asymmetries as well as the ability of participants to adjust their aiming trajectories following an unexpected change to the inertial resistance to movement. In Experiment 1, participants (N = 11) were able to rapidly adjust their movement trajectories to conform to the new movement requirements. They were faster and more consistent when aiming with their right hand than with their left hand, regardless of whether or not the movement was perturbed. In Experiment 2, participants' (N = 11) vision of the hand was manipulated so that the role of visual feedback in the corrective process could be examined. Vision had an impact not only on performance but also on the characteristics of the movement trajectories. Manual asymmetries in aiming were associated with a right hand superiority during the final corrective stages of the movement.