Performance and Learning of Generalized Motor Programs: Relative (GMP) and Absolute (Parameter) Errors

The effects of practice (Experiment 1) and parameter variability (Experiment 2) on the learning of generalized motor programs (GMPs) and movement parameterization were investigated In each experiment, 2 tasks with different relative force-time structures were tested. Participants (N = 32, Experiment (N = 40, Experiment 2) attempted to exert a pattern of force that resembled in force and time a waveform that was displayed on a computer monitor. In both experiments, the analysis suggested that the GMP, although refined over practice, was relatively stable (i.e., resistant to decay and interference), even early in practice (after 20 trials). In addition, the results indicated that constant and variable parameter practice did not differentially affect GMP learning but did degrade the learning of the parameter that was not varied. The data provided additional evidence for the dissociation of the GMP and the parameterization processes proposed in GMP theory. Contrary to schema theory, the present data suggest an interdependence between the force and the time parameters: The manipulation of 1 of the parameters has a negative effect on the learning of the other parameter.     

Predictive Pointing Movements and Saccades Toward a Moving Target

The authors investigated whether and, if so, how velocity information is used to control predictive manual pointing movements and saccades. Participants (N = 6) intercepted an occluded moving target as if it were still visible. They kept their eyes fixated while the target moved. The target traveled over a fixed distance and changed its velocity on the way. The presentation time of the final velocity was varied. Both the eye and the hand overshot the slow target and undershot the fast target, particularly when the duration of the final velocity was short. Thus, responses were biased in the direction of the target's initial velocity. The error seemed to arise because participants did not take their latency into account when aiming at the target. Instead, they strategically aimed farther ahead when the target was fast. Amplitude was also more related to the position of velocity change than to final velocity duration. Both findings suggest that target velocity is not extrapolated but that individuals add an increment to the position of velocity change.     

Motivational Effects of Outcome Feedback on Motor Performance

This study examined the effects of success and failure feedback on subsequent motor performance. Based upon the general motivation (or level-of-aspiration) hypothesis, initial success should lead to better subsequent performance than does initial failure, while the reverse prediction was derived from the cognitive dissonance theory. To test these rival hypotheses, two experiments were conducted on undergraduate male students (n =120) performing a motor maze task. Initial failure improved subjects’ subsequent performance, thus supporting the dissonance theory. However, this effect was observed only under low-ego-involving conditions, thereby suggesting that the effects of dissonance and ego involvement are interdependent. The findings were discussed in terms of motivational and informational/attributional effects of outcome feedback on motor performance.     

The Impact of Real and Illusory Perturbations on the Early Trajectory Adjustments of Goal-Directed Movements

Examinations of goal-directed movements reveal a process of control that operates to make adjustments on the basis of the expected visual afference associated with the limb's movement. This experiment examined the impact of perturbations to the perceived and actual velocity of aiming movements when each was presented alone or in tandem with the other. Perturbations to perceived velocity were achieved by translating the background over which aiming movements were performed. An aiming stylus that discharged air either in the direction of the movement or in the direction opposite the movement generated the actual velocity perturbations. Kinematic analyses of the aiming movements revealed that only the actual perturbation influenced the control of early movement trajectories. The results are discussed with respect to the influence that visual information has on the control exerted against physical perturbations. Speculations are raised regarding how potential for perturbations influences the strategies adopted for minimizing their impact.     

The Use of Location and Distance in Reproducing Different Amplitudes of Movement

Experiments have demonstrated that in order to reproduce a standard movement, subjects can move for a certain distance or move to a certain location. Available evidence tentatively suggests the use of distance for short movements and location for long movements. However, this evidence is in conflict with the motor short-term memory characteristics of short and long movements. An experiment is reported which demonstrates that subjects spontaneously use distance for short movements and location for long movements, the procedure adopted being to shift by small amounts the starting-point of the estimation movements and test for a consequent shift in the end-point of the estimation. The experiment also revealed that using distance or location to reproduce a 40° movement resulted in equal accuracy, suggesting that the use of large amplitudes of movement has caused previous investigators to find that distance is less accurate than location.     

The Discriminating Properties of an Optoelectronic Movement Analysis Method in Patients With Parkinsonism

Several partly overlapping diseases have Parkinsonism as a symptom and tools that may differentiate between these disorders would be helpful. The authors evaluated the discriminating properties of the objective automated posturo-locomotor-manual (PLM) L-DOPA test in regard to health, and the movement disorders Parkinson's disease (PD), multiple system atrophy (MSA), and progressive supranuclear palsy (PSP). A PLM test–retest procedure was performed in healthy controls (n = 37) and results were compared with PLM L-DOPA tests performed by 132 patients with Parkinsonism in intermediate to advanced stages (56 PD, 53 MSA, 23 PSP). The movement time (MT) for the standardized movement and its different components was measured. The discriminating abilities of individual, or combinations of, test variables were determined by forward stepwise multiple logistic regression and evaluated with receiver-operating characteristic (ROC) analysis. Each PLM variable separated healthy persons from patients with Parkinsonism before administration of L-DOPA (area under the curve (AUC) = 0.94–0.99, p <.001 for any separate variable). A combination of (MT_off – MT_on)/MT_off and MT_on had the highest ability to separate patients with PD from patients with atypical Parkinsonism (area under the curve = 0.91, p <.001). The PLM test discriminates between healthy controls and patients with Parkinsonism, and between patients with Parkinson's disease and patients with atypical Parkinsonism.

[Supplementary material is available for this article. Go to the publisher's online edition of Journal of Motor Behavior for the following free supplemental resource: supplementary data.]     

Visual and Proprioceptive Determinants of Space Perception and Movement

The present study determined the relationship between perception of the upright in 2-dimensional space and movement accuracy. 161 female Ss were administered the Rod and Frame Test, and 30 Ss, whose scores indicated the greatest and least error in perceptual differentiation, were assigned to 2 experimental groups and measured on accuracy of postural pursuit tracking. The effects of direction of movement and visual field conditions on accuracy of performance were determined by a coordinate postural platform and hybrid computer methods. A direct relationship existed between perception of the vertical in space and accuracy of motor responses and that perceptual integration was affected by the direction of movement and the presence of a stable visual field.     

Gender-Specific Movement Strategies Using a Computer-Pointing Task

Females typically demonstrate a movement time advantage for tasks requiring high levels of manual dexterity, whereas males are notably better at targeting activities. According to D. Kimura (2000), the hunter-gatherer hypothesis primarily accounts for those performance advantages; that dichotomy fails, however, when one makes movement outcome predictions for tasks that are not clearly fine-motor or interceptive in nature. Investigators have recently proposed that time constraints (M. Peters, 2005) and gender-specific response style differences (M. Peters & P. Campagnaro, 1996; L. E. Rohr, 2006) affect motor performance. Here, the author used a computer-pointing task measuring both movement error and movement time in 16 participants to further investigate response style differences. Kinematic and linear regression analyses between resultant error and both movement time and task difficulty reinforced the notion that gender-specific movement biases emphasize speed and accuracy, respectively, for men and women.     

Sequential and Biomechanical Factors Constrain Timing and Motion in Tapping

The authors examined how timing accuracy in tapping sequences is influenced by sequential effects of preceding finger movements and biomechanical interdependencies among fingers. Skilled pianists tapped sequences at 3 rates; in each sequence, a finger whose motion was more or less independent of other fingers' motion was preceded by a finger to which it was more or less coupled. Less independent fingers and those preceded by a more coupled finger showed large timing errors and change in motion because of the preceding finger's motion. Motion change correlated with shorter intertap intervals and increased with rate. Thus, timing of sequence elements is not independent of the motion trajectories that individuals use to produce them. Neither motion nor its relation to timing is invariant across rates.     

The Cascade Neural Network Model and a Speed-Accuracy Trade-Off of Arm Movement

We propose a hybrid neural network model of aimed arm movements that consists of a feedforward controller and a postural controller. The cascade neural network of Kawato, Maeda, Uno, and Suzuki (1990) was employed as a computational implementation of the feedforward controller. This network computes feedforward motor commands based on a minimum torque-change criterion. If the weighting parameter of the smoothness criterion is fixed and the number of relaxation iterations is rather small, the cascade model cannot calculate the exact torque, and the hand does not reach the desired target by using the feedforward control alone. Thus, one observes an error between the final position and the desired target location. By using a fixed weighting parameter value and a limited iteration number to simulate target-directed arm movements, we found that the cascade model generated a planning time–accuracy trade-off, and a quasi–power-law type of speed–accuracy trade-off. The model provides a candidate neural mechanism to explain the stochastic variability of the time course of the feedforward motor command. Our approach also accounts for several invariant features of multijoint arm trajectories, such as roughly straight hand paths and bell-shaped speed profiles.