Romeo Chua

Visual regulation of manual aiming

Abstract Traditional models of visuomotor control have generally emphasized the importance of vision in the guidance of limb movements. Vision is thought to subserve the modificational processes underlying the control of these movements. The objectives of the present work were to elaborate upon the role of vision in the regulation of an ongoing limb movement, address issues pertaining to the nature of this regulation, and examine predictions of the Optimized Submovement Model (Meyer, Abrams, Kornblum, Wright and Smith 1988) of limb control. An aiming task was adopted in which subjects were required to displace a graphics cursor on a monitor toward a target. The presence of visual feedback proved to be a potent determinant of performance. In experiment 1, superior performance consistency with visual feedback was attribute to the prevalence of discrete and continuous modifications made to the movement when visual information was available. In experiment 2, the same visually-based performance advantage was found. However, this advantage was no longer related to the presence of adjustments to the movement. The present results are discussed with reference to current issues in the nature of visuomotor regulation and their implications toward the Optimized Submovement Model.

Discrete vs. continuous visual control of manual aiming

Abstract Two experiments were conducted to examine the influence of instructional set and vision on the kinematics and end-point accuracy of a simple target-aiming movement. While instructional set had a large impact on the velocity and acceleration patterns of the movements, the availability of vision before and during the movement was the best predictor of accuracy. Although subjects were more accurate in a full vision condition than in two visually degraded conditions, subjects made no more discrete adjustments to the movement trajectory. These data suggest that the visual control of aiming may occur in a continuous fashion.

Asymmetries in Coupling Dynamics of Perception and Action.

The influence of information-based dynamics on coordination dynamics of rhythmic movement was examined with special reference to the expression of asymmetries. In Experiment 1, right-handed subjects performed unimanual, rhythmical movements in coordination with either a discrete or continuous visual display. The right hand-visual display system defined a more stable perception-action collective than the left, particularly when continuous visual information was available. In Experiment 2, the same subjects performed rhythmic bimanual movements in coordination with a continuous visual display. The action collective was inherently more stable than the perception-action collective, although similar patterns were observed at both levels. Importantly, the dynamics of the perception-action collective impinged upon the dynamics of the action collective in terms of stability. Asymmetries remained evident between limbs in the bimanual preparations, with the left hand exhibiting greater limit-cycle variability and also a tendency to more often effect transitions at the action couple. Features of dynamical models that capture characteristics of manual asymmetries are discussed.

The contribution of vision to asymmetries in manual aiming.

An experiment was conducted to examine the hypothesis that the right hand system is superior in the processing of visual information. A manual aiming task utilizing four visual conditions was employed. In the full-vision (FV) condition subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off (AO) condition, the room lights were extinguished at movement initiation, thus preventing vision of the moving limb. The target remained illuminated. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. Ambient illumination and thus vision of the hand remained present. Finally there was a no-vision (NV) condition in which ambient illumination was removed and the target was extinguished upon initiation of the response movement. Although the manipulation of vision had potent effects upon terminal accuracy, and influenced reaction and movement time measures, the hands did not differ in the extent to which these characteristics were expressed. A left hand advantage for reaction time was observed. This may reflect a relative increase in right hemisphere involvement prior to aiming movements which are spatially complex.

Asymmetries in the Regulation of Visually Guided Aiming

An experiment was conducted to examine the contribution of sensory information to asymmetries in manual aiming. Movements were performed in four vision conditions. In the full-vision condition (FV), subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off condition (AO), the room lights were extinguished at movement initiation, preventing vision of the moving limb. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. In a no-vision (NV) condition, ambient illumination was removed and the target was extinguished upon initiation of the response movement. Results indicated that accuracy was superior in the full-vision and target-off conditions and when movements were made by the right hand. Movements made by the right hand were also of shorter mean duration. The magnitudes of performance asymmetries were uninfluenced by vision condition. Analyses of movement kinematics revealed that movements made in conditions in which there was vision of the limb exhibited a greater number of discrete modifications of the movement trajectory. On an individual-trial basis, no relationship existed between accuracy and the occurrence of discrete modifications. These data suggest that although vision greatly enhances accuracy, discrete modifications subserved by vision reflect the imposition of nonfunctional zero-order control processes upon continuous higher-order control regimes.

Optimizing the use of vision in manual aiming: the role of practice.

The purpose of this study was to determine how subjects learn to adjust the characteristics of their manual aiming movements in order to make optimal use of the visual information and reduce movement error. Subjects practised aiming (120 trials) with visual information available for either 400 msec or 600 msec. Following acquisition, they were transferred to conditions in which visual information was available for either more or less time. Over acquisition, subjects appeared to reduce target-aiming error by moving to the target area more quickly in order to make greater use of vision when in the vicinity of the target. With practice, there was also a reduction in the number of modifications in the movement. After transfer, both performance and kinematic data indicated that the time for which visual information was available was a more important predictor of aiming error than the similarity between training and transfer conditions. These findings are not consistent with a strong “specificity of learning” position. They also suggest that, if some sort of general representation or motor programme develops with practice, that representation includes rules or procedures for the utilization of visual feedback to allow for the on-line adjustment of the goal-directed movement.

The influence of intermittent vision on manual aiming.

Two experiments were conducted to examine the influence of intermittent vision on right and left hand aiming. In Experiment 1, increased visual occlusion times led to a steady deterioration in performance that was most pronounced for high index of difficulty targets. Longer visual sample times only partially compensated for this effect (Experiment 2). It is suggested that a short-lived visual representation of the movement environment may in some cases provide a reasonable, although not perfect, substitute for direct visual pickup. In Experiment 2, there was some indication that the right hand system may be faster at using visual information than the left hand system.

The role of impulse variability in manual-aiming asymmetries

SummaryTwo experiments are reported in which we examined the hypothesis that the advantage of the right hand in target aiming arises from differences in impulse variability. Subjects made aiming movements with the left and right hands. The force requirements of the movements were manipulated through the addition of mass to the limb (Experiments 1 and 2) and through control of movement amplitude (Experiment 1). Although the addition of mass diminished performance (i. e., it increased movement times in Experiment 1 and increased error in Experiment 2), the two hands were not differently affected by the manipulation of required force. In spite of the fact that the right hand exhibited enhanced performance (i. e., lower movement times in Experiment 1 and greater accuracy in Experiment 2), these advantages were not reflected in kinematic measures of impulse variability.

The influence of age on manual asymmetries in movement preparation and execution

An experiment was conducted to examine the influence of age on the expression of manual asymmetries in movement preparation and execution and the implication toward the hypothesis of differential hemispheric aging. Young, middle age, and elderly subjects performed a simple pointing task under a precuing paradigm (Rosenbaum, 1980). Although elderly subjects were slower in initiating and completing their movements compared to younger subjects, they demonstrated the same right‐hand advantage for the speed of movement execution and exhibited the same left‐hand advantage for speed of preparation as the younger subjects. These results indicate that elderly subjects exhibit the same pattern of manual asymmetry as younger subjects. Furthermore, elderly subjects exhibited a more pronounced left‐hand advantage than younger subjects for movement preparation. This finding is not consistent with the idea that right‐hemisphere visuospatial function deteriorates more rapidly with age.

Effects of schizophrenia and prefrontal leukotomy on movement preparation and generation

The purpose of this study was to investigate the ability of leukotomized and unleukotomized schizophrenic patients to use advance information in the process of movement preparation. Subjects participated in an aiming task in which movements could be defined on the basis of hand used to perform the task, and distance travelled to the target. Subjects were provided with full, partial, or no prior information about the upcoming movement by either precueing hand, distance, both hand and distance, or by providing no precue. The leukotomized and unleukotomized schizophrenic patients were able to use this advance information to facilitate the speed of their responses in much the same way as did subjects in a normal control group. These results are discussed in terms of models of movement preparation, and the role of the frontal lobes in schizophrenia and movement planning.