Outflow and inflow in movement duplication

Investigation of how accurately individuals with hemiparetic stroke can mirror their forearm positions

Current literature suggests that greater than 50% of survivors of a stroke cannot accurately perceive where their upper extremity is positioned. Our recent work demonstrates that the extent to which this perception is affected can depend on how the task is performed. For example, individuals with stroke who have a deficit in mirroring the position of their passively-placed paretic forearm during a between-arms task may accurately reproduce the position of their actively-controlled paretic forearm during a single-arm task. Moreover, the ability of individuals with various types of unilateral lesions to locate their thumb can depend on whether they reach for their paretic thumb or non-paretic thumb. Consequently, we investigated to what extent the accuracy of individuals post-hemiparetic stroke in mirroring forearm positions on a between-arms task is influenced by various conditions. Eighteen participants with hemiparetic stroke rotated their reference forearm to a target position, and then rotated their opposite forearm to concurrently mirror the position of their reference forearm. This task was performed when participants referenced each forearm (paretic, non-paretic) at two target positions (extension, flexion) for two modes of limb control (passive, active). We quantified for every testing scenario of each participant their position-mirroring error. The number of times for which participants were classified as having a deficit was least when mirroring forearm positions at the flexed position when referencing their non-paretic forearm. Additionally, the difference in the magnitude of errors when participants referenced each arm was greater during active than passive movements. Findings from this study provide further evidence that the accuracy with which individuals post stroke perceive the position of their limbs can depend on how a task is performed. Factors to consider include whether movements are active versus passive, which limb is referenced, and where the limb is positioned.

Ability of individuals with chronic hemiparetic stroke to locate their forearms during single-arm and between-arms tasks

Background

According to between-arms assessments, more than 50% of individuals with stroke have an impaired position sense. Our previous work, which employed a clinical assessment and slightly differing tasks, indicates that individuals who have a deficit on a between-forearms position-localization task do not necessarily have a deficit on a single-forearm position-localization task.

Objective

Our goal here was to, using robotics tools, determine whether individuals with stroke who have a deficit when matching forearm positions within an arm also have a deficit when mirroring forearm positions between arms, independent of the arm that leads the task.

Methods

Eighteen participants with chronic hemiparetic stroke and nine controls completed a single-arm position-matching experiment and between-arms position-mirroring experiment. For each experiment, the reference forearm (left/right) passively rotated about the elbow joint to a reference target location (flexion/extension), and then the participant actively rotated their same/opposite forearm to match/mirror the reference forearm’s position. Participants with stroke were classified as having a position-matching/-mirroring deficit based on a quantitative threshold that was derived from the controls’ data.

Results

On our single-arm task, one participant with stroke was classified as having a position-matching deficit with a mean magnitude of error greater than 10.7° when referencing their paretic arm. Position-matching ability did not significantly differ for the controls and the remaining seventeen participants with stroke. On our between-arms task, seven participants with stroke were classified as having a position-mirroring deficit with a mean magnitude of error greater than 10.1°. Position-mirroring accuracy was worse for these participants with stroke, when referencing their paretic arm, than the controls.

Concluding remark

Findings underscore the need for assessing within-arm position-matching deficits, in addition to between-arms position-mirroring deficits when referencing each arm, to comprehensively evaluate an individual’s ability to locate their forearm(s).

Proprioceptive identification of joint position versus kinaesthetic movement reproduction

Regarding our voluntary control of movement, if identification of joint position, that is independent of the starting condition, is stronger than kinaesthetic movement reproduction, that implies knowledge of the starting position and movement's length for accuracy, is still a matter of debate in motor control theories and neuroscience. In the present study, we examined the mechanisms that individuals seem to prefer/adopt when they locate spatial positions and code the amplitude of movements. We implemented a joint position matching task on a wrist robotic device: this task consists in replicating (i.e. matching) a reference joint angle in the absence of vision and the proprioceptive acuity is given by the goodness of such matching. Two experiments were carried out by implementing two different versions of the task and performed by two groups of 15 healthy participants. In the first experiment, blindfolded subjects were asked to perform matching movements towards a fixed target position, experienced with passive movements that started from different positions and had different lengths. In the second experiment, blindfolded subjects were requested to accurately match target positions that had a different location in space but were passively shown through movements of the same length. We found a clear evidence for higher performances in terms of accuracy (0.42±0.011/°) and precision (0.43±0.011/°) in the first experiment, therefore in case of matching positions, rather than in the second where accuracy and precision were lower (0.36±0.011/° and 0.35±0.011/° respectively). These results suggested a preference for proprioceptive identification of joint position rather than kinaesthetic movement reproduction.

Impact of motor task execution on an individual's ability to mirror forearm positions

This work is motivated by our goal of determining why individuals with stroke are impaired when locating their arms in space. We assessed the ability of individuals without neurological impairments to mirror their forearms during various motor tasks so that we could identify baseline performance in an unimpaired population. Nine right-hand dominant participants without neurological impairments mirrored forearm positions bi-directionally (i.e., right forearm mirrors left forearm, vice versa) for three motor tasks (i.e., passive, passive/active, and active) and two position identification modes (i.e., mirroring to a position stored in working memory versus concurrently felt by the opposite arm). During each trial, the participant's reference forearm moved to a flexion ([Formula: see text]) or extension ([Formula: see text]) position, and then, their opposite forearm mirrored the position of their reference forearm. The main finding across all tested conditions is that participants mirrored forearm positions with an average magnitude of error [Formula: see text]. When controlling their forearms' movements (active motor task), participants mirrored forearm positions more accurately by up to, on average, [Formula: see text] at the flexion location than at the extension location. Moreover, participants mirrored forearm positions more accurately by up to, on average, [Formula: see text] when their forearms were moved for them rather than when they controlled their forearms' movements. Task directionality and position identification mode did not significantly affect participant arm mirroring accuracy. These findings are relevant for interpreting in future work the reason why impairments occur, on similar tasks, in individuals with altered motor commands, working memory, and arm impedance, e.g., post-stroke hemiparesis.

Perception of Movement Patterns. Recognition from Visual Arrays of Distorted Patterns

A review of literature indicates that the perception and memory of movement patterns with kinaesthesis might be expected to differ depending on whether a movement pattern is actively commanded or passively induced. In addition, it has been suggested that kinaesthesis is a gross sense in the absence of vision. An attempt was made to demonstrate differences between the perception and memory of actively commanded movement patterns, passively induced movement patterns, and visual patterns formed by a moving light. A visual recognition test was employed. While it was apparent that the recognition task was a sensitive one for testing the accuracy of pattern perception, no significant difference was demonstrated between the three movement conditions.

Preselection and response biasing in short-term motor memory

Two experiments were performed comparing preselected (subject defined) and constrained (experimenter defined) movements. In the first experiment, subjects made reproduction responses immediately or under unfilled and filled 15-sec retention intervals. Results indicated that recall of preselected movements was clearly superior until the interpolation of information processing activity. In addition, preselected movements demonstrated no forgetting over a 15-sec retention interval while constrained movements evidenced spontaneous memory lass, suggesting that preselected movements possess a stronger representation in memory. The second experiment examined this interpretation in a response biasing paradigm. Subjects made criterion responses under preselected or constrained conditions, while the interpolated movement was always in the constrained mode and ± 40 deg from the criterion. The subjects' task was to attend to both movements and recall each when instructed. While preselected recall was clearly superior' to constrained recall, response biasing was clearly evident in both. The failure to find differential biasing effects was discussed in terms of the relative trace strength hypothesis (Stelmach & Welsh, 1972).

Adaptation to novel visuo-motor transformations: further evidence of functional haptic neglect

Studies with perturbed and augmented haptic information during adaptation to novel visuo-motor transformations suggest that haptic information might be neglected. However, the notion of functional haptic neglect during adaptation is counterintuitive for different reasons. Therefore, we sought conditions where haptic guidance during adaptation results in benefits. First, we mixed guided and unguided trials during practice with a visuo-motor rotation. In two experiments, we found no indication of an advantage of the guidance groups over the no-guidance control groups. In the third experiment, the visuo-motor transformation was a pure time delay because motor timing has been hypothesized to profit from haptic guidance. Again, there was no evidence of benefits for the guidance group. Thus, the findings of this series of experiments provide further evidence of the claim that haptic information is neglected during adaptation to a visuo-motor transformation.

Task-dependent asymmetries in the utilization of proprioceptive feedback for goal-directed movement

Whereas the majority of studies regarding upper limb asymmetries in motor performance have focused on preferred arm dominance for producing motor output, studies exploring the role of sensory feedback have suggested that the preferred and non-preferred arms are specialized for different aspects of movement. A recent study by Goble et al. (2006) found evidence of a non-preferred left arm (and presumably right hemisphere) proprioceptive dominance for a target matching task that required subjects to both memorize and transfer across hemispheres proprioceptive target information. This paradigm contrasted previous studies of proprioceptive matching asymmetry that explored only memory-based matching and produced equivocal results. The purpose of the present study, therefore, was to examine task-dependent asymmetries in proprioceptive matching performance, including differences related to active versus passive presentation of the matching target. It was found that the non-preferred left arm of right handers matched target elbow angles more accurately than the preferred arm, but only in the matching condition that required both memory and interhemispheric transfer. Task-dependent asymmetries were not affected by the mode of target presentation and assessment of matching kinematics revealed differences in strategy for both the speed and smoothness of targeted movements. Taken together, these results suggest that the non-preferred arm/hemisphere system is specialized for the processing of movement-related proprioceptive feedback.

Movement Cue Reproduction Under Preselection

A series of three experiments was undertaken to determine the role of prior knowledge of different movement cues in the preselection effect. Experiments 1 and 2 examined the singular and combinative role of location and extent cues under both preselected and constrained conditions. The third experiment provided a framework for evaluating the sources of informations which may contribute to the preselection phenomenon. In experiments 1 an 2, the results suggest the advantage of preseleted over constrained movement was constant across movement cues. The second experiment demonstrated that the dual cue condition was superior to location alone and extent alone in both accuracy and consistency. Finally, the third experiment indicated that prior knowledge (strategy) was the primary variable responsible for the preselection effect.

Complex movement patterns: learning retention and sources of error in recall

In this study of kinaesthesis, the learning, retention, and recall of complex patterns was examined. Subjects were blindfolded, held a stylus in the right hand, and moved around stencil patterns, either actively or passively. The patterns were recalled with a free active movement of the right hand, after various amounts of practice, immediately or after a 60–s interval, once or twice in succession, with and without visual guidance. The shape and size of the drawings was compared with the criterion patterns. The effect of practice varied depending on whether the criterion movement was active or passive, and on the measure of recall performance. Even when the criterion patterns were freely practised, the recall traces showed large errors in shape and systematic shrinkage in size, and there were large individual differences. Regardless of these errors, recall performance was reliable. The effect of an unfilled retention interval varied as a function of practice. When the patterns were recalled under visual guidance, there was no shrinkage in the size of the drawings.

The Role of Planning and Efference in the Recall of Location and Distance Cues in Short-Term Motor Memory

Previous studies have suggested that the superior accuracy of preselected (subject-defined) over constrained (experimenter-defined) movements is due to both the availability of a movement plan and efferent-command information. The present experiment examined the contribution of the planning and efferent components to the preselection effect in a location and a distance task. The availability of a movement plan was manipulated by providing preselected and constrained groups of subjects with a rehearsal movement. Furthermore, the amount of efferent information available was varied by requiring both active and passive rehearsal movements. The results suggested that while strategy alone is responsible for the superiority of preselected location, both strategy and efferent information underlie the superiority of preselected distance reproduction.

Attention to Visual Feedback in Motor Learning

Visual guidance and movement to a stop were used to train subjects to make a simple movement without experiencing error in practice. Movement to a stop led to test performance as accurate as that after training with KR, but visual guidance did not. If a continuous visual cue as well as a stop were present during practice, subjects also performed less accurately, although they did not need to attend to the visual cue. All types of training were better than no training at all. Results are discussed in terms of the role of visual feedback in the development and assessment of programs for movement.

Perceptions of movement patterns: recall of movement

The present study attempted to characterize the perception retention, and recall of kinaesthetic information regarding movement sequences (patterns). An attempt was made to draw on and extend conclusions relevant to simple movements (movement amplitude). One group of 10 blindfolded subjects recalled criterion movement patterns that had been actively commanded and 10 subjects recalled passively induced movements. The following conclusions were made. (1) Previous reports of algebraic errors in the recall of simple movement amplitudes are consistency with the finding that criterion perimeter, area, and depth of features were underestimated when recalled. (2) Measures of the accuracy of kinaesthetic perception do not alone account for the generally low level of pattern recall, the large range of individual differences or the underestimation of amplitude. The process of percept formation and of translating a percept into recalled movement are implicated. (3) Conclusions based on the short-term retention and recall of simple movements do not account for the coding, retention, and recall of movement sequences (patterns). (4) Percepts were formed, and patterns were recalled as a sequence of features but not as a sequence of key positions. (5) No direct difference was demonstrated between the recall of actively commanded and passively induced criterion movement patterns. However, the finding of a high gross angle change in the active condition was explained in terms of an unfavourable interaction between corollary discharge and sensory information.

An alternative test of the adams-creamer decay hypothesis in timing motor responses

Ss were randomly assigned to either a vestibular proprioception (VP) group (N = 30) or a no vestibular proprioception (NVP) group (N = 30). The VP group was tested while supine on a table rotated 60 deg. in the vertical plane and, at the cessation of rotation, Ss estimated a 2-sec. interval. Procedures were identical for the NVP group with the exception that they received no body rotation. All Ss received 40 trials and knowledge of results was given during a 20-sec. intertrial interval. The VP group had significantly smaller mean absolute and algebraic error scores than the NVP group. The difference between the mean variable error scores of the two groups was not significant. Results supported the Adams-Creamer decay hypothesis in terms of absolute error scores and algebraic error scores, but did not support the hypothesis in terms of variable error scores.