The influence of advance information on the response complexity effect in manual aiming movements

Working memory involvement in action planning does not include timing initiation structure

A fundamental limitation in the type of information that can be retained in working memory is identified in this theoretical / review article. The analysis is based on studies of skilled motor performance that were not initially conceived in terms of working memory. Findings from a long history of experimentation involving reaction time (RT) prior to making a brief motor response indicate that although the parameters representing the goal to be achieved by the response can be retained in working memory, the control code that implements timing of action components cannot. This lack of working memory requires that the "timing code" must be compiled immediately prior to the moment that it is to be utilized; it is not possible to be fully ready to respond earlier. This compiling process increases RT and may also underlie both the psychological refractory period effect and the difficulty of generating concurrent motor actions with independent timing. These conclusions extend, but do not conflict with, other models of working memory.

The influence of foreperiod duration on the preparation and control of sequential aiming movements

Reaction time (RT) and movement times (MTs) to the first target are typically longer for two-target sequential movements compared to one-target movements. While this one-target advantage has been shown to be dependent on the availability of advance information about the numbers of targets, there has been no systematic investigation of how foreperiod duration (i.e., interval between presentation of the target(s) and stimulus) influences the planning and execution of sequential movements. Two experiments were performed to examine how the one-target advantage is influenced by the availability and timing of advance target information. In Experiment 1, participants performed one- and two-target movements in two separate blocks. In Experiment 2, target conditions were randomised from trial to trial. The interval between target(s) appearing and stimulus tone (i.e., foreperiod) was varied randomly (0, 500, 1,000, 1,500, and 2,000 ms). The results of Experiment 1 revealed that while the one-target advantage in RT was not influenced by foreperiod duration, the one-target advantage in MT increased as foreperiod duration increased. The variability of endpoints at the first target was greater in the two- compared to one-target condition. In Experiment 2, the one-target advantage in both RT and MT increased as the length of the foreperiod increased. However, there was no difference in limb trajectory variability between target conditions. The implication of these findings for theories of motor planning and execution of multiple segment movements is discussed.

Choice reaction time can be influenced by intervention protocols after stroke: A systematic review

INTRODUCTION

Post-stroke individuals usually present a delay in choice reaction time (CRT), and it would be important to verify the efficacy in the reduction of CRT after intervention protocols.

OBJECTIVE

The main question of this review is 'What are the characteristics of the CRT test and the interventions that decrease the CRT?'

STUDY DESIGN

Systematic review.

METHODS

The search was performed in March 2019 using the electronic databases, PubMed, Science Direct, Scopus, Web of Science, Lilacs, Cinahal, Cochrane, Ovid, Scielo, PEDro, and Embase. There was no restriction regarding publication dates, and studies written in English that were conducted on poststroke patients and presented CRT results were included.

RESULTS

Six studies were included in this systematic review, and the majority showed varied objectives, methodologies, and groups, regarding the number and characteristics of the sample, varying from complex to simple tasks for the CRT evaluation.

CONCLUSION

This review suggests the investigation of the CRT in stroke patients with functional tasks using auditory and/or visual stimulus. About the CRT training in stroke patients, this review also suggests bilateral training, including functional tasks, and the use of structural practice blocks, but more studies are needed to better demonstrate the effects of interventions on the CRT.

REGISTRATION NUMBER

PROSPERO (protocol no. CRD42017073995).

Evidence for distinct steps in response preparation from a delayed response paradigm

Task parameters still affect reaction times even when all necessary information for executing an action is presented prior to a Go signal to execute the action. Hypotheses in terms of short-term memory capacity, residual activation, and a separate motor-programming stage have been suggested to explain what can and cannot be prepared prior to a delayed Go signal. To test these hypotheses, we used a delayed response task, in which participants were to initiate a movement at onset of an imperative Go signal following the target stimulus. Across Experiments 1-3 we varied task properties including stimulus type, information uncertainty and response complexity, respectively, while controlling other factors. We also varied the time available to process the response by randomly varying the interval between onset of the target and the Go signal (i.e., the stimulus onset asynchrony, or SOA). If the preparation process is completed before initiation, the examined factor should display a strong interaction with SOA, with its effect disappearing at long SOAs. Our results showed strong, weaker, and no interaction patterns for the three factors, respectively, favoring the separate stage hypothesis, according to which response preparation is separated into steps to arrange kinematic specifications into muscle-controllable terms.

What's your number? The effects of trial order on the one-target advantage

When moving our upper-limb towards a single target, movement times are typically shorter than when movement to a second target is required. This is known as the one-target advantage. Most studies that have demonstrated the one-target advantage have employed separate trial blocks for the one- and two-segment movements. To test if the presence of the one-target advantage depends on advance knowledge of the number of segments, the present study investigated whether the one-target advantage would emerge under different trial orders/sequences. One- and two-segment responses were organized in blocked (i.e., 1-1-1, 2-2-2), alternating (i.e., 1-2-1-2-1-2), and random (i.e., 1-1-2-1-2-2) trial sequences. Similar to previous studies, where only blocked schedules have typically been utilized, the one-target advantage emerged during the blocked and alternate conditions, but not in the random condition. This finding indicates that the one-target advantage is contingent on participants knowing the number of movement segments prior to stimulus onset.

Better together: Contrasting the hypotheses explaining the one-target advantage

Movement times are significantly shorter when moving from a start position to a single target, compared to when one has to continue onto a second target (i.e., the one-target advantage [OTA]). To explain this movement time difference, both the movement integration and the movement constraint hypotheses have been proposed. Although both hypotheses have been found to have explanatory power as to why the OTA exists, the support for each has been somewhat equivocal. The current review evaluated the relative support in the literature for these two hypotheses. Ultimately, preferential support for each theoretical explanation was found to be related to the higher indices of difficulty (IDs: Fitts, 1954) employed. That is, studies that included higher IDs (i.e., 6-8 bits) were more likely to provide more support for the movement constraint hypothesis, whereas studies employing lower IDs (i.e., 1-4 bits) were more likely to provide more support for the movement integration hypothesis. When the IDs employed were relatively intermediate (i.e., 5 bits), both hypotheses were mostly supported. Thus, task difficulty is crucial when determining which hypothesis better explains the planning and control of sequential goal-directed movements. Critically, the OTA most likely always involves integration but may also involve constraining if the accuracy demands are sufficiently high.

Ipsilesional Arm Aiming Movements After Stroke: Influence of the Degree of Contralesional Impairment

The authors examined the effects of the degree of impairment of the contralesional upper limb and the side of the hemispheric damage on ipsilesional upper limb performance in chronic stroke individuals. Right- and left-side stroke resulting in mild-to-severe impairment and healthy participants took part in simple and choice reaction time tasks involving aiming movements. The stroke individuals performed the aiming movements with the ipsilesional upper limb using a digitizing tablet to ipsi- or contralateral targets presented in a monitor. The global performance of the group with severe right hemispheric damage was worse than that of the other groups, indicating that the side of hemispheric damage and degree of motor impairment can adversely affect aiming movement performance.

A motor planning stage represents the shape of upcoming movement trajectories

Interactions with our environment require curved movements that depend not only on the final position of the hand but also on the path used to achieve it. Current studies in motor control, however, largely focus on point-to-point movements and do not consider how movements with specific desired trajectories might arise. In this study, we examined intentionally curved reaching movements that navigate paths around obstacles. We found that the preparation of these movements incurred a large reaction-time cost. This cost could not be attributed to nonmotor task requirements (e.g., stimulus perception) and was independent of the execution difficulty (i.e., extent of curvature) of the movement. Additionally, this trajectory representation cost was not observed for point-to-point reaches but could be optionally included if the task encouraged consideration of straight trajectories. Therefore, when the path of a movement is task relevant, the shape of the desired trajectory is overtly represented as a stage of motor planning. This trajectory representation ability may help explain the vast repertoire of human motor behaviors.

The integration of sequential aiming movements: Switching hand and direction at the first target

Movement times to a single target are typically shorter compared to when movement to a second target is required. This one target movement time advantage has been shown to emerge when participants use a single hand throughout the target sequence and when there is a switch between hands at the first target. Our goal was to investigate the lacuna in the movement integration literature surrounding the interactive effects between switching hands and changing movement direction at the first target. Participants performed rapid hand movements in five conditions; movements to a single target; two target movements with a single hand in which the second target required an extension or reversal in direction; and movements to two targets where the hands were switched at the first target and the second target required an extension or reversal in direction. The significance of including these latter two (multiple hand-multiple direction) movements meant that for the first time research could differentiate between peripheral and central processes within movement integration strategies. Reaction times were significantly shorter in the single task compared to the two target tasks. More importantly, movement times to the first target were significantly shorter in the single target task compared to all two target tasks (reflecting the so-called one target advantage), except when the second movement was a reversal movement with the same hand. These findings demonstrate for the first time the contrasting effects of movement integration at central and peripheral levels.

Common vs. independent limb control in sequential vertical aiming: The cost of potential errors during extensions and reversals

The following study explored movement kinematics in two-component aiming contexts that were intended to modulate the potential cost of overshoot or undershoot errors in up and down directions by having participants perform a second extension movement (Experiment 1) or a reversal movement (Experiment 2). For both experiments, the initial movement toward a downward target took longer, and had lower peak acceleration and peak velocity than upward movements. These movement characteristics may reflect a feedback-based control strategy designed to prevent energy-consuming limb modifications against gravitational forces. The between-component correlations of displacement at kinematic landmarks (i.e., trial-by-trial correlation between the first and second components) increased as both components unfolded. However, the between-component correlations of extensions were primarily negative, while reversals were positive. Thus, movement extensions appear to be influenced by the use of continuous on-line sensory feedback to update limb position at the second component based on the position attained in the first component. In contrast, reversals seem to be driven by pre-planned feedforward procedures where the position of the first component is directly replicated in the second component. Finally, the between-component correlations for the magnitude of kinematic landmarks showed that aiming up generated stronger positive correlations during extensions, and weaker positive correlations toward the end of the first component during reversals. These latter results suggest the cost of potential errors associated with the upcoming second component directly influence the inter-dependence between components. Therefore, the cost of potential errors is not only pertinent to one-component discrete contexts, but also two-component sequence aims. Together, these findings point to an optimized movement strategy designed to minimize the cost of errors, which is specific to the two-component context.

Sequential actions: effects of upcoming perceptual and motor tasks on current actions

Reports of spatial interactions between current and upcoming elements in a movement sequence could be due to intentional planning of a "global" action sequence (i.e., strategic effects), or to unintentional motor planning arising from merely paying attention to upcoming target objects (i.e., interference effects). The purpose of this experiment was to determine whether paying attention to an upcoming target object could induce kinematic changes in a current grasping action when there is no strategic advantage associated with such changes. Specifically, participants grasped a rectangular target object in the presence of a second rectangular object that was either ignored, or was the target of a subsequent grasping or perceptual judgment task. Peak grip aperture during the primary grasping action was assessed in relation to the size of the second rectangle. The results revealed an effect of the second rectangle's size only when it was the target of a subsequent perceptual judgment task. This result calls into question the assumption that interactions between current and subsequent elements of an action sequence are necessarily due to strategic movement planning processes and might instead arise from interference arising from merely paying attention to nontarget objects.

Uncertainty in aiming movements and its association to hand function

AbstractThe purpose of this study was to analyze the influence of the uncertainty of target location on the planning and execution of aiming movements performed towards the ipsilateral and contralateral directions by the right and left upper limbs. In addition, the association between the performance of aiming movements and the performance of functional manual tasks was investigated. Two tasks were proposed: with prior knowledge of the movement direction (simple reaction time) or not (choice reaction time). The grip strength and manual dexterity were measured. The choice option in response (i.e. uncertainty) influenced planning of the aiming movements, but not its execution, while movements performed towards the contralateral direction were worse in execution as compared to the ipsilateral direction. Manual dexterity was significantly correlated with reaction times, while the performance during movement execution was significantly correlated with handgrip/pinch strength.

Sequential aiming with one and two limbs: effects of target size

It is well reported that movement times to the first target in a two-target sequence are slower than when a single target response is required. This one-target advantage has been shown to emerge when the two-target sequence is performed with the same limb and when the first and second segments within the sequence are performed with different limbs (i.e., when there is a switch between limbs at the first target). The present study examined the functional dependency between response segments in both single and two limb sequential aiming by varying the accuracy demands at the first and second target. Results revealed that, for both one and two limb conditions, the one-target advantage was present with large first targets but not with small first targets. Additionally, when the first target was large and the second target was small, spatial variability at the first target was significantly less (or constrained more) in both one and two limb conditions compared to conditions requiring only a single target response. These findings suggest that similar principles underlie the one-target advantage in both single and two limb sequential movements.

Differential beta-band event-related desynchronization during categorical action sequence planning

A primate study reported the existence of neurons from the dorso-lateral prefrontal cortex which fired prior to executing categorical action sequences. The authors suggested these activities may represent abstract level information. Here, we aimed to find the neurophysiological representation of planning categorical action sequences at the population level in healthy humans. Previous human studies have shown beta-band event-related desynchronization (ERD) during action planning in humans. Some of these studies showed different levels of ERD according to different types of action preparation. Especially, the literature suggests that variations in cognitive factors rather than physical factors (force, direction, etc) modulate the level of beta-ERD. We hypothesized that the level of beta-band power will differ according to planning of different categorical sequences. We measured magnetoencephalography (MEG) from 22 subjects performing 11 four-sequence actions - each consisting of one or two of three simple actions - in 3 categories; ‘Paired (ooxx)’, ‘Alternative (oxox)’ and ‘Repetitive (oooo)’ (‘o’ and ‘x’ each denoting one of three simple actions). Time-frequency representations were calculated for each category during the planning period, and the corresponding beta-power time-courses were compared. We found beta-ERD during the planning period for all subjects, mostly in the contralateral fronto-parietal areas shortly after visual cue onset. Power increase (transient rebound) followed ERD in 20 out of 22 subjects. Amplitudes differed among categories in 20 subjects for both ERD and transient rebound. In 18 out of 20 subjects ‘Repetitive’ category showed the largest ERD and rebound. The current result suggests that beta-ERD in the contralateral frontal/motor/parietal areas during planning is differentiated by the category of action sequences.

Similar Mechanisms of Movement Control in Target- and Effect-Directed Actions toward Spatial Goals?

Previous research has shown that actions conducted toward temporal targets and temporal effects are controlled in a similar way. To investigate whether these findings also apply to spatially restricted movements we analyzed movement kinematics of continuous reversal movements toward given spatial targets and toward self-produced spatial effects in two experiments. In Experiment 1 target- and effect-directed movements were investigated in three different goal constellations. A spatial target/effect was always presented/produced on one movement side, on the other side either (a) no target/effect, (b) the same target/effect, or (c) a more difficult target/effect was presented/produced. Results showed that both target-directed and effect-directed movements have a typical spatial kinematic pattern and that both can be equally well described by linear functions as suggested by Fitts’ Law. However, effect-directed movements have longer movement times. In Experiment 2 participants performed target-directed movements to the one side and effect-directed movements to the other side of a reversal movement. More pronounced spatial kinematics were observed in effect-directed than in target-directed movements. Together, the results suggest that actions conducted toward spatial targets and spatial effects are controlled in a similar manner. Gradual differences in the kinematic patterns may arise because effects are cognitively more demanding. They may therefore be represented less accurately than targets. However, there was no indication of qualitative differences in the cognitive representations of effects and targets. This strengthens our assumption that both targets and effects play a comparable role in action control: they can both be viewed as goals of an action. Thus, ideomotor theories of action control should incorporate action targets as goals similar to action effects.

Influence of cueing on the preparation and execution of untrained and trained complex motor responses

This study investigated the influence of cueing on the performance of untrained and trained complex motor responses. Healthy adults responded to a visual target by performing four sequential movements (complex response) or a single movement (simple response) of their middle finger. A visual cue preceded the target by an interval of 300, 1000, or 2000 ms. In Experiment 1, the complex and simple responses were not previously trained. During the testing session, the complex response pattern varied on a trial-by-trial basis following the indication provided by the visual cue. In Experiment 2, the complex response and the simple response were extensively trained beforehand. During the testing session, the trained complex response pattern was performed in all trials. The latency of the untrained and trained complex responses decreased from the short to the medium and long cue-target intervals. The latency of the complex response was longer than that of the simple response, except in the case of the trained responses and the long cue-target interval. These results suggest that the preparation of untrained complex responses cannot be completed in advance, this being possible, however, for trained complex responses when enough time is available. The duration of the 1st submovement, 1st pause and 2nd submovement of the untrained and the trained complex responses increased from the short to the long cue-target interval, suggesting that there is an increase of online programming of the response possibly related to the degree of certainty about the moment of target appearance.

Preparation for voluntary movement in healthy and clinical populations: evidence from startle

In this review we provide a summary of the observations made regarding advance preparation of the motor system when presenting a startling acoustic stimulus (SAS) during various movement tasks. The predominant finding from these studies is that if the participant is prepared to make a particular movement a SAS can act to directly and quickly trigger the prepared action. A similar effect has recently been shown in patients with Parkinson's disease. This "StartReact" effect has been shown to be a robust indicator of advance motor programming as it can involuntarily release whatever movement has been prepared. We review the historical origins of the StartReact effect and the experimental results detailing circumstances where advance preparation occurs, when it occurs, and how these processes change with practice for both healthy and clinical populations. Data from some of these startle experiments has called into question some of the previously held hypotheses and assumptions with respect to the nature of response preparation and initiation, and how the SAS results in early response expression. As such, a secondary focus is to review previous hypotheses and introduce an updated model of how the SAS may interact with response preparation and initiation channels from a neurophysiological perspective.

The dual role of vision in sequential aiming movements

Previous research has demonstrated that movement times to the first target in sequential aiming movements are influenced by the properties of subsequent segments. Based on this finding, it has been proposed that individual segments are not controlled independently. The purpose of the current study was to investigate the role of visual feedback in the interaction between movement segments. In contrast to past research in which participants were instructed to minimize movement time, participants were set a criterion movement time and the resulting errors and limb trajectory kinematics were examined under vision and no vision conditions. Similar to single target movements, the results indicated that vision was used within each movement segment to correct errors in the limb trajectory. In mediating the transition between segments, visual feedback from the first movement segment was used to adjust the parameters of the second segment. Hence, increases in variability that occurred from the first to the second target in the no vision condition were curtailed when visual feedback was available. These results are discussed along the lines of the movement constraint and movement integration hypotheses.

Sequential aiming with two limbs and the one-target advantage

Movement times to the first target in a 2-target sequence are typically slower than in 1-target aiming tasks. The 1-target movement time advantage has been shown to emerge regardless of hand preference, the hand used, the amount of practice, and the availability of visual feedback. The authors tested central and peripheral explanations of the 1-target advantage, as postulated by the movement integration hypothesis, by asking participants to perform single-target movements, 2-target movements with 1 limb, and 2-target movements in which they switched limbs at the first target. Reaction time and movement time data showed a 1-target advantage that was similar for both 1- and 2-limb sequential aiming movements. This outcome demonstrates that the processes underlying the increase in movement time to the 1st target in 2-target sequences are not specific to the limb, suggesting that the 1-target advantage originates at a central rather than a peripheral level.

Reflexive limb selection and control of reach direction to moving targets in cats, monkeys, and humans

When we reach for an object, we have to decide which arm to use and the direction in which to move. According to the established view, this is voluntarily controlled and programmed in advance in time-consuming and elaborate computations. Here, we systematically tested the motor strategy used by cats, monkeys, and humans when catching an object moving at high velocity to the left or right. In all species, targets moving to the right selectively initiated movement of the right forelimb and vice versa for targets moving to the left. Movements were from the start directed toward a prospective target position. In humans, the earliest onset of electromyographic activity from start of motion of the target ranged from 90 to 110 ms in different subjects. This indicates that the selection of the arm and specification of movement direction did not result from the subject's voluntary decision, but were determined in a reflex-like manner by the parameters of the target motion. As a whole the data suggest that control of goal-directed arm movement relies largely on an innate neuronal network that, when activated by the visual signal from the target, automatically guides the arm throughout the entire movement toward the target. In the view of the present data, parametric programming of reaching in advance seems to be superfluous.

The preparation and control of reversal movements as a single unit of action

Previous research has demonstrated that movement time and kinematic properties of limb trajectories to the first target of a two-target reversal movement differ to that of single-target responses. In the present study we investigated whether two-target reversal movements are organized as a single unit of action or two separate components by perturbing the number of targets prior to and during movement execution. In one experiment, participants performed single-target movements and on one-third of the trials a second target was presented either at target presentation, movement onset or peak velocity. On those trials in which a second target was presented, participants were required to complete their movement to the first target and then move to the second target. In a second experiment, the reverse was the case with participants performing two-target movements that changed to single-target movement on one-third of the trials. A two-target movement time advantage was observed only when the required response was specified prior to movement initiation. Also, participants failed to prevent movement towards the second target when the requirements of the task changed from a two-target to single-target response at movement onset or later. These results indicate that two-target reversal movements were organized as a single unit of action prior to response initiation.