Oscillations in Motor Priming: Positive Rebound Follows the Inhibitory Phase in the Masked Prime Paradigm

From among the diverse meanings of stability, the one the author adopts here is that the effects of a perturbation are opposed, and therefore small effects remain small. Except in linear systems, however, instability need not lead to unbounded motion and may actually be desirable when maneuverability is important. Moreover, properties of nerves, muscles, and tendons present serious challenges to stabilization. A review of observations from the motor control literature reveals that responses to perturbations in many common situations assist rather than resist the perturbation and are therefore presumably destabilizing. The observations encompass situations of position maintenance as well as impending or ongoing movement. The author proposes that the motor control system responds to a sudden perturbation by a pattern of muscle activity that mimics an accustomed voluntary movement, oblivious of stability considerations. What prevents runaway motion in the face of short-term instability appears to be voluntary intervention.     

Movement-Produced Feedback as a Mechanism For The Temporal Anticipation of Motor Responses

That part of the input hypothesis of motor timing behavior which postulates that movement-produced feedback can serve as a mechanism for the temporal anticipation of motor responses was tested. 32 male college Ss temporally anticipated (no preview) the coincidence of a moving pointer with a stationary one and executed the timing response with his right hand while either a high (HFB) or low (LFB) level of movement-produced feedback was indirectly manipulated in the left arm. The HFB group temporally anticipated with greater accuracy than the LFB group which supported that part of the input hypothesis being tested. Apparently, Ss were relying on proprioceptive feedback about the position of their left arm movement to cue the timing response of their right hand.     

Immediate Movement History Influences Reach-to-Grasp Action Selection in Children and Adults

The authors review studies of mentally simulated movements. In automatic or cyclical movements, actual and motor imagery (MI) durations are similar. When athletes simulate only dynamic phases of movement or perform MI just before competing, however, environmental and time constraints lead to an underestimation of actual duration. Conversely, complex attention-demanding movements take longer to image. Finally, participants can modify the speed of MI voluntarily when they receive specific instructions. To complete the available data, the authors compared imagined and actual durations in tennis and gymnastics. Results showed systematic and disproportionate overestimation of actual duration. The authors found a relationship between complex motor skills and MI duration. They discuss the factors leading to over- and underestimation and the hypotheses that could be tested.     

How do Motor Systems Deal with the Problems of Controlling Three-Dimensional Rotations?

Rotations are fundamental to motor control, not only for orienting to stimuli but also in the joint articulations that underlie translational movements. Studying three-dimensional (3-D) rotations of the simplest joint system, the eye, has provided general insights into the neural control of movement. First, in selecting one 3-D eye orientation for each two-dimensional (2-D) gaze direction, the oculomotor system generates a behavior called Listing's law that constrains eye position to a 2-D plane, Listing's plane. This selection is made internally by an inverse kinematic transformation called the Listing's law operator. Second, the oculomotor system incorporates the inherent multiplicative relationship between rotational velocity and position to generate the 3-D movement and position commands required by Listing's law. Finally, the coordinate systems for these commands appear to align with Listing's plane rather than with anatomic structures. Recent investigations have revealed similar behavioral constraints in the orientations of the head and arm, suggesting that the neural mechanisms for Listing's law may have analogues in many motor systems.     

Evidence of Incomplete Motor Programming in Parkinson's Disease

One of the essential questions regarding movement deficits in Parkinson's disease (PD) is whether they stem from impaired selecting and switching among movements, impaired use of predictive information to prepare movement, or impaired execution of movement. PD subjects (n = 9) and age-matched control subjects (n = 8) performed a cued, sequential-response RT task. The cue provided either no information, accurate information, or inaccurate information about the upcoming response. PD subjects used predictive information to prepare and to switch among movement sequences normally, but second and third key press latencies were prolonged in comparison with the first key press latency. In Experiments 2 and 3, the effects of choice set and sequence length on key press latencies were examined. These results provide evidence that PD subjects initiate movement before the entire response sequence is prepared. PD does not impair motor programming or execution processes themselves but impairs the smooth coordination of those processes.     

Rapid Aimed Limb Movements: Differential Effects of Practice on Component Submovements

Three experiments are reported in which subjects practiced rapid aimed limb movements (arm pointing and wrist rotation) toward a visible target region. Subjects were required to minimize their movement durations while still landing in the target. The movement trajectories were examined to assess the effects of practice on separate component submovements of the limb movements. The results revealed that practice improved primarily temporal, not spatial, aspects of performance. Practice reduced the overall movement durations, but had different effects on the individual submovements: Practice allowed subjects to reduce the amount of time spent performing final corrective submovements, but actually increased slightly the time needed to produce the initial ballistic submovement. The results suggest that practice in the present task primarily enhanced the ability to use feedback information, but there was also some evidence of changes in the ballistic, preprogrammed portion of the movements. The results demonstrate that analysis of submovements can reveal important details of the underlying motor control processes.     

Gross Motor Performance in Minimally Brain Injured Children

As a pre-requisite to curriculum development, the characteristics of the gross motor performance of special education classes of minimally brain injured boys and girls were described. In general, age changes in mean performance were linear, the scores of the boys being the superior. The level of performance very closely resembled that of comparison groups of educable mentally retarded children from the same school districts.     

The Effect of Rest Following Massed Practice of Continuous and Discrete Motor Tasks

Theories of the rest-related phenomena of reminiscence and warm-up decrement regard them as independent, being due to different factors. In this study it was found that rest following massed practice of a continuous task increased performance (reminiscence) and rest following massed practice of a discrete task lowered performance (warm-up decrement). The near-zero correlation found between the phenomena indicates that they are indeed independent and task-specific. Implications of the findings for the prediction of the effect of rest, and the fact that much motor learning and performance is task-specific, is discussed.     

Bimanual and Unimanual Convergent Goal-Directed Movement Times

Three experiments are reported, investigating the effects of using 1 or 2 hands when making convergent low index of difficulty (ID) and visually controlled movements (2 hands meeting together). The experiments involved movements in four different cases—a probe held in the right hand and moved to a target held in the stationary left hand, vice versa of this arrangement, both hands moving with the probe in the right hand and target in the left hand, and vice-versa of this arrangement. Experiments were the standard Fitts’ paradigm, moving a pin into a hole and a low-ID task. In Fitts’ task, 2-hand movements were faster than 1 hand only at higher IDs; this was also the case in the pin-to-hole transfer task and the movement times were lower when the pin was held in the preferred hand. Movements made with low ID showed a small effect of 1- or 2-handed movements, with the effective amplitude of the movement being reduced by about 20% when 2 hands were used.     

Control of Integrated Task Sequences Shapes Components of Reaching

Reaching toward an object usually consists of a sequence of elemental actions. Using a reaching task sequence, the authors investigated how task elements of that sequence affected feedforward and feedback components of the reaching phase of the movement. Nine right-handed adults performed, with their dominant and nondominant hands, 4 tasks of different complexities: a simple reaching task; a reach-to-grasp task; a reach-to-grasp and lift object task; and a reach-to-grasp, lift, and place object task. Results showed that in the reach-to-grasp and lift object task more time was allocated to the feedforward component of the reach phase, while latency between the task elements decreased. We also found between-hand differences, supporting previous findings of increased efficiency of processing planning-related information in the preferred hand. The presence of task-related modifications supports the concept of contextual effects when planning a movement.