James Lyons

Goal-Directed Aiming: Two Components but Multiple Processes

This article reviews the behavioral literature on the control of goal-directed aiming and presents a multiple-process model of limb control. The model builds on recent variants of Woodworths (1899) two-component model of speed-accuracy relations in voluntary movement and incorporates ideas about dynamic online limb control based on prior expectations about the efferent and afferent consequences of a planned movement. The model considers the relationship between movement speed and accuracy, and how performers adjust their trial-to-trial aiming behavior to find a safe, but fast, zone for movement execution. The model also outlines how the energy and safety costs associated with different movement outcomes contribute to movement planning processes and the control of aiming trajectories. Our theoretical position highlights the importance of advance knowledge about the sensory information that will be available for online control and the need to develop a robust internal representation of expected sensory consequences. We outline how early practice contributes to optimizing strategic planning to avoid worst-case outcomes associated with inherent neural-motor variability. Our model considers the role of both motor development and motor learning in refining feed-forward and online control. The model reconciles procedural and representational accounts of the specificity-of-learning phenomenon. Finally, we examine the breakdown of perceptual-motor precision in several special populations (i.e., Down syndrome, Williams syndrome, autism spectrum disorder, normal aging) within the framework of a multiple-process approach to goal-directed aiming.

Optimal Control Strategies Under Different Feedback Schedules: Kinematic Evidence

Abstract Two experiments were conducted in which participants (N = 12, Experiment 1; N = 12, Experiment 2) performed rapid aiming movements with and without visual feedback under blocked, random, and alternating feedback schedules. Prior knowledge of whether vision would be available had a significant impact on the strategies that participants adopted. When they knew that vision would be available, less time was spent preparing movements before movement initiation. Participants also reached peak deceleration sooner but spent more time after peak deceleration adjusting limb trajectories. Consistent with those findings, analysis of spatial variability at different points in the trajectory indicated that variability increased up to peak deceleration but then decreased from peak deceleration to the end of the movement.

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.

Does Joe influence Fred's action?: Inhibition of return across different nervous systems

Inhibition of return (IOR) refers to the slowing of responses to a target that appears in the same location as a previous event. Many researchers have speculated that IOR arises from inhibitory neural processes that have developed through evolution to facilitate efficient search patterns by biasing the action and/or attention of an individual towards novel locations. Throughout evolution, however, humans conducted searches as individuals as well as members of a group. In this context, we sought to determine if IOR could also be observed in the behavior of one individual after the observation of anothers behavior. Consistent with our reasoning, there was no difference in the magnitude of the IOR effect found when participants followed their own response or the response of their partner. These results are discussed in the context of action-based attention and possible underlying neural mechanisms.

Sensory Attenuation of Self-Produced Feedback: The Lombard Effect Revisited

The Lombard effect describes the automatic and involuntary increase in vocal intensity that speakers exhibit in a noisy environment. Previous studies of the Lombard effect have typically focused on the relationship between speaking and hearing. Automatic and involuntary increases in motor output have also been noted in studies of finger force production, an effect attributed to mechanisms of sensory attenuation. The present study tested the hypothesis that sensory attenuation mechanisms also underlie expression of the Lombard effect. Participants vocalized phonemes in time with a metronome, while auditory and visual feedback of their performance were manipulated or removed during the course of the trial. We demonstrate that providing a visual reference to calibrate somatosensory-based judgments of current vocal intensity resulted in reduced expression of the Lombard effect. Our results suggest that sensory attenuation effects typically seen in fingertip force production play an important role in the control of speech volume.

Optimizing rapid aiming behaviour: Movement kinematics depend on the cost of corrective modifications.

Recent studies have shown that the initial impulse associated with goal-directed aiming movements typically brings the limb to a position short of the target. This is because target overshooting is associated with greater temporal and energy costs than target undershooting. Presumably these costs can be expected to vary not only with the muscular forces required to move the limb, but also the gravitational forces inherent in the aiming task. In this study we examined the degree to which primary movement endpoint distributions depend on the direction of the movement with respect to gravity. We hypothesized that the magnitude of an undershoot bias would be greatest for downward movements because target overshooting necessitates a time and energy consuming movement reversal against gravity. Participants completed rapid aiming movements toward targets located above and below, as well as proximal and distal to a central home position. Movements were made both with and without additional mass attached to the limb. Although movement time did not vary with experimental condition, primary movement endpoint distributions were consistent with our predictions. Specifically, both greater undershooting and greater endpoint variability was associated with downward aiming movements. As well, a greater proportion of the overall movement time was spent in the corrective phase of the movement. These results are consistent with models of energy minimization that posit an inherent efficiency of control and hold that movements are organized to minimize movement time and energy expenditure and maximize mechanical advantages.

Hand, Space and Attentional Asymmetries in Goal-Directed Manual Aiming*

Two experiments were conducted to explore the interaction of the two cerebral hemispheres in motor control, by examining hand, space and attentional asymmetries in goal-directed aiming. In Experiment 1, right-handed subjects moved to targets more quickly with their right hand than their left hand. In addition, each hand was faster when moving in its own hemispace. Although in a control condition, movements were initiated more quickly with the left hand, visual distractors disrupted left hand performance more than right hand performance. For contralateral aiming, ipsilateral distractors caused the greatest interference. In Experiment 2, when targets and distractors were all presented at the midline, a right hand advantage was found for movement time along with a left hand advantage for reaction time, independent of target and distractor location. Our findings are discussed in terms of a right hemisphere role in movement preparation and the allocation of attention in space, and greater left hemisphere involvement in movement execution.

Action representations in perception, motor control and learning: implications for medical education.

Medical Education 2011: 45: 119–131

Within- and between-nervous-system inhibition of return: Observation is as good as performance

Inhibition of return (IOR) has been shown to occur when an individual returns to a target location (within-person IOR) and when an individual moves to a location just engaged by another individual (between-person IOR). Although within- and between-person IOR likely result from the same inhibitory mechanisms, different processes must activate these mechanisms following the performance and observation of action. Consistent with the suggestion that the mirror neuron system may be responsible for activating the inhibitory mechanisms behind IOR on observation trials, between-person IOR was only detected under restricted viewing conditions known to activate mirror neurons. These results indicate that mirror neuron system may be involved in both higher-order and automatic cognitive behavior.

The utilization of visual information in the control of rapid sequential aiming movements

Two experiments were conducted to examine the role of vision in the execution of a movement sequence. Experiment 1 investigated whether individual components of a sequential movement are controlled together or separately. Participants executed a rapid aiming movement to two targets in sequence. A full vision condition was compared to a condition in which vision was eliminated while in contact with the first target. The size of the first target was constant, while the second target size was varied. Target size had an influence on movement time and peak velocity to the first target. Vision condition and target size did not affect the time spent on the first target. These results suggest that preparation of the second movement is completed before the first movement is terminated. Experiment 2 examined when this preparation occurred. A full vision condition was compared to a condition in which vision was occluded during the flight phase of the first movement. Movement initiation times were shorter when vision was continually available. Total movement time was reduced with vision in two-target condition, but not in a control one-target condition. The time spent on the first target was greater when vision was not available during the first movement component. The results indicate that vision prior to movement onset can be used to formulate a movement plan to both targets in the sequence [Fischman & Reeve (1992).