George E. Stelmach

Cognition and Motor Processes

I Motor Control and Action Planning.- 1 Cognitivism and Future Theories of Action: Some Basic Issues.- 2 A Distributed Processing View of Human Motor Control.- 3 The Apraxias, Purposeful Motor Behavior, and Left-Hemisphere Function.- 4 A Motor-Program Editor.- 5 Eye Movement Control During Reading: The Effect of Word Units.- II Motor Contributions to Perception and Cognition.- 6 Motor Theories of Cognitive Structure: A Historical Review.- 7 Context Effects and Efferent Factors in Perception and Cognition.- 8 Saccadic Eye Movements and Visual Stability: Preliminary Considerations Towards a Cognitive Approach.- 9 Scanning and the Distribution of Attention: The Current Status of Herons Sensory-Motor Theory.- 10 The Relationship Between Motor Processes and Cognition in Tactile Vision Substitution.- III Mediating Structures and Operations Between Cognition and Action.- 11 Mechanisms of Voluntary Movement.- 12 Evaluation: The Missing Link Between Cognition and Action.- 13 Modes of Linkage Between Perception and Action.- 14 The Contribution of Vision-Based Imagery to the Acquisition and Operation of a Transcription Skill.- 15 Speech Production and Comprehension: One Lexicon or Two?.- IV Attention, Cognition, and Skilled Performance.- 16 S-Oh-R: Oh Stages! Oh Resources!.- 17 Automatic Processing: A Review of Recent Findings and a Plea for an Old Theory.- 18 Motor Learning as a Process of Structural Constriction and Displacement.- V Interactions Between Cognition and Action in Development.- 19 Cognition and Action in Development: A Tutorial Discussion.- 20 Biodynamic Structures, Cognitive Correlates of Motive Sets and the Development of Motives in Infants.- 21 Discontinuity in the Development of Motor Control in Children.- Author Index.

Parkinsonism Reduces Coordination of Fingers, Wrist, and Arm in Fine Motor Control

This experiment investigates movement coordination in Parkinsons disease (PD) subjects. Seventeen PD patients and 12 elderly control subjects performed several handwriting-like tasks on a digitizing writing tablet resting on top of a table in front of the subject. The writing patterns, in increasing order of coordination complexity, were repetitive back-and-forth movements in various orientations, circles and loops in clockwise and counterclockwise directions, and a complex writing pattern. The patterns were analyzed in terms of jerk normalized for duration and size per stroke. In the PD subjects, back-and-forth strokes, involving coordination of fingers and wrist, showed larger normalized jerk than strokes performed using either the wrist or the fingers alone. In the PD patients, wrist flexion (plus radial deviation) showed greater normalized jerk in comparison to wrist extension (plus ulnar deviation). The elderly control subjects showed no such effects as a function of coordination complexity. For both PD and elderly control subjects, looping patterns consisting of circles with a left-to-right forearm movement, did not show a systematic increase of normalized jerk. The same handwriting patterns were then simulated using a biologically inspired neural network model of the basal ganglia thalamocortical relations for a control and a mild PD subject. The network simulation was consistent with the observed experimental results, providing additional support that a reduced capability to coordinate wrist and finger movements may be caused by suboptimal functioning of the basal ganglia in PD. The results suggest that in PD patients fine motor control problems may be caused by a reduced capability to coordinate the fingers and wrist and by reduced control of wrist flexion.

Adaptation to gradual as compared with sudden visuo-motor distortions

Abstract If visual feedback is discordant with movement direction, the visuo-motor mapping is disrupted, but can be updated with practice. In this experiment subjects practiced discrete arm movements under conditions of visual feedback rotation. One group was exposed to 10°-step increments of visual feedback rotation up to a total of 90°, a second group to a 90° visual feedback rotation throughout the experiment. After the first group reached the 90° visual feedback rotation, its subjects performed faster, with less spatial error, and showed larger aftereffects than the subjects who practiced constantly under the 90° visual feedback rotation condition. Results suggest that gradually increasing feedback distortion allows more complete adaptation than a large, sudden distortion onset.

The preparation and production of isometric force in Parkinson's disease

Subjects with Parkinsons disease (PD) and age-matched controls performed an isometric force production task, aiming at different target force levels without concurrent force feedback. Overall, PD subjects were as accurate as controls in attaining the target force levels, but executed the task differently. They had longer times to peak force and contraction durations, larger impulses and lower rates of force development, and force-time profiles with many more irregularities. They also initiated lower force contractions with longer latencies, unlike controls. The data suggest that PD subjects are deficient in the regulation of force and time parameters, rather than simply in force production. The ability to produce peak forces accurately limits the generality of previous assertions that PD subjects are heavily dependent on concurrent visual feedback.

Age Related Decline in Postural Control Mechanisms

In order to study voluntary and reflexive mechanisms of postural control, young and elderly persons were given large-fast and small-slow ankle-rotation postural disturbances while standing on a movable platform capable of measuring ground reaction forces. Large-fast rotations were employed to activate long-loop reflexes, and small-slow rotations were employed to tap the higher level sensory integration aspects of postural control. Overall, the elderly persons exhibited more perturbation induced sway and showed a slowing in voluntary, as opposed to reflexive mechanisms of correcting postural disturbance. For both age groups, reflexive mechanisms were found to be relatively intact. When small perturbations were given, the elderly persons swayed more than young participants and produced sporadic reflexive activity. Moreover, elderly persons did not adapt to the small perturbations and exhibited increased postural sway to repetitive presentation of the perturbation, whereas young participants substantially decreased their postural sway. These data demonstrate that elderly persons are at some disadvantage when posture is under the control of slower, higher level sensory integrative mechanisms.

Cognitive-motor abilities of the elderly driver.

This article reviews literature that documents the effects of age on motor performance as it relates to driving behavior. Movement initiation is the focal point of the first part of the article, and it is considered in terms of absolute age differences when functional manipulations are made, such as response preparation, response selection, response programming, and complexity. The second part of the article addresses age difference in the context of movement execution characteristics; differences in movement speed, force production, limb coordination, and sensory motor integration are considered. Movement time and movement kinematics and kinetics are the principal dependent measures reviewed. Adults were found to initiate and execute movements more slowly and with less precision as they age, which may contribute to the decline of their driving skill. Most of the data reviewed were obtained in laboratory settings; nevertheless, they suggest how age may impair the elderly driver.

Persistence in visual feedback control by the elderly

Abstract Young and elderly subjects performed aiming movements to a visual target with a manipulandum to determine whether the elderly reduce their reliance on visual feedback after extended practice. Reliance on visual feedback was assessed by performance on trials in which the cursor displaying arm movement was unpredictably extinguished. Movements were divided into two subcomponents: a primary, ballistic submovement and a secondary, corrective submovement. For both age groups, removal of visual feedback prior to practice resulted in a decrease in the distance covered in the primary submovement, an increase in the distance of the secondary submovement, and a decrease in endpoint accuracy. After extensive practice with the cursor present, the proportion of distance traveled with the primary submovement was again assessed under trial conditions in which the cursor randomly disappeared. Following practice, the young demonstrated that they were capable of extending the primary submovement distance closer to the target. In addition, primary submovement distance was unaffected by the removal of vision following practice. After practice the elderly did not show evidence of lengthening the primary submovement, and submovement distance and endpoint accuracy continued to be altered by the removal of vision. This suggests that, unlike the young, the elderly do not benefit from practice so that they can place a greater proportion of the movement under program control. Thus, on a relative basis, a greater proportion of their overall movement requires corrective adjustments.

Control theories in motor behavior

Abstract The goal of contemporary motor control theorist is the delineation of the “language” of movements. That is, in what unambiguous code are the parameters of movement specified, given the composition of the human body? In this pursuit not only are the elements of the language of movement sought, but the rules of combination or syntax of movement are also to be derived. This paper compares a number of motor control theories according to the form of control they exhibit and according to their ability to address issues in the area. Recurring theoretical trends in motor control are examined and the evidence for each is reviewed, emphasizing their explanatory power in the classical problems of control: motor equivalence (Hebb 1949), complexity (Bernstein 1967), and variability (Glencross 1980; Schmidt 1975, 1976).

The effect of viewing the static hand prior to movement onset on pointing kinematics and variability

Pointing accuracy and arm movement kinematics of six human subjects were measured in three conditions where the hand was never visible during the ongoing movement: (1) in the dark; (2) the static hand was seen in peripheral vision prior to target presentation, but not during the reaction time (H−T); (3) the static hand was seen in peripheral vision until movement onset (H+T). It was shown that: (1) viewing the hand prior to movement decreased pointing variability as compared to the dark condition. (2) Viewing simultaneously hand and target (H+T) further decreased pointing variability as compared to the H−T condition. This effect was proportional to the reaction time. (3) A lengthening of the deceleration phase was observed for movements performed in the H + T condition, as compared to the other two conditions. (4) A negative correlation between variability and the first part of the deceleration phase was observed in the H + T condition, but neither in the H-T condition nor in the dark. These results suggest that the decrease in pointing variability observed in the H + T condition is due to a feedback based on kinesthetic reafference. Better encoding of the initial position of the hand relative to the target (as in H + T) would allow a calibration of arm position sense, which is used to drive the hand toward the target during the deceleration phase.

Orienting the finger opposition space during prehension movements.

Two experiments are reported that examined the act of prehension when subjects were asked to grasp with their thumb and index finger pads an elongated object resting horizontally on a surface and placed at different orientations with respect to the subject. In Experiment 1, the pad opposition preferences were determined for the six angles of orientation examined. For angles of 90 degrees (object parallel to frontal plane) or less, no rotation of the wrist (pronation) was used; for angles 110 degrees or greater, pronation was systematically employed to reorient the finger opposition space. Only one angle, 100 degrees , produced any evidence of ambiguity in how to grasp the object: Approximately 60% of these grasps involved pronation and 40% did not. Using the foregoing grasp preference data, in Experiment 2 we examined the kinematics of the wrist and elbow trajectories during prehension movements directed at an object in different orientations. Movement time, time to peak acceleration, velocity, and deceleration were measured. No kinematic differences were observed when the object orientation either required (110 degrees ) or did not require (80 degrees ) a pronation. By contrast, if the orientation was changed at the onset of the movement, such that an unpredicted pronation had to be introduced to achieve the grasp, kinematics were affected: Movement time was increased, and the time devoted to deceleration was lengthened. These data are interpreted as evidence that when natural prehension occurs, pronation can be included in the motor plan without affecting the movement kinematics. When constraints are imposed on the movement execution as a consequence of a perturbation, however, the introduction of a pronation component requires kinematic rearrangement.