A guide to performing difficult bimanual coordination tasks: just follow the yellow brick road

Both discrete and continuous bimanual coordination patterns are difficult to effectively perform when the two limbs are required to perform different movements patterns, move at different velocities and/or move different amplitudes unless some form of integrated feedback is provided. The purpose of the present experiment was to determine the degree to which a complex bimanual coordination pattern could be performed when integrated feedback and movement template are provided. The complex bimanual coordination pattern involved reciprocal movements of the two limbs under different difficulty requirements. As defined by Fitts’ index of difficulty (ID), the left arm (ID = 3, A = 16°, W = 4°) task was of lower difficulty than the right arm task (ID = 5, A = 32°, W = 2°). Note that the left and right limb movements are also different in terms of movement time, movement velocity, accuracy requirements and amplitude as well as one movement was continuous and the other intermittent. Participants were provided 2 blocks of 9 trials in the bimanual condition (30 s/trial). Following the bimanual phase, participants performed two unimanual test trials—one with each limb. The results demonstrated that the performance for each limb in the bimanual condition was similar to the performance for the same limb and conditions in the unimanual control conditions. The similarity was indicated by the same movement speed, movement structure, endpoint variability and hit rates for the bimanual and unimanual conditions. The results support our hypothesis that people can overcome the intrinsic difficulties associated with performing complex bimanual coordination patterns when provided appropriate perceptual information feedback that allows them to detect and correct coordination errors.     

Optimizing the control of high ID movements: rethinking the obvious

An experiment was designed to determine the degree to which instruction and visual display influence participants?? performance and control characteristics when executing difficult reciprocal aiming movements. Participants were randomly assigned to one of the three acquisition conditions (Fitts, Impulse and Sine). Participants in the Fitts condition were asked to flex/extend their limb/lever in the horizontal plane at the elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. In the Impulse condition, participants moved between two target lines paced by a metronome, and in the Sine condition, participants were asked to track a sine wave pattern. The timing for the Impulse and Sine conditions was set to result in total times (movement time?+?dwell time) similar to that observed in our previous experiments using the same Fitts conditions. The respective display and current position of the limb were projected on the screen in front of the participant. Following nine acquisition trials (15?s each) under their assigned condition, Test 1 was conducted under the same conditions as the participant experienced during the acquisition, and then, Test 2 was conducted for all participants under the Fitts?? conditions. The results for Test 1 indicated that total time and movement time for the three groups did not differ. However, dwell time was significantly lower, a larger proportion of movement time was spent in the acceleration portion of the movement, and peak velocity was significantly lower for the participants in the Sine condition than for participants in the Fitts condition. On Test 2, where Fitts conditions were imposed, the Sine group outperformed the Fitts condition on all variables except hits and endpoint variability where the Fitts and Sine groups performed similarly.     

Pointing with the ankle: the speed-accuracy trade-off

This study investigated the trade-off between speed and accuracy in pointing movements with the ankle during goal-directed movements in dorsal–plantar (DP) and inversion–eversion (IE). Nine subjects completed a series of discrete pointing movements with the ankle between spatial targets of varying difficulty. Six different target sets were presented, with a range of task difficulty between 2.2 and 3.8 bits of information. Our results demonstrated that for visually evoked, visually guided discrete DP and IE ankle pointing movements, performance can be described by a linear function, as predicted by Fitts’ law. These results support our ongoing effort to develop an adaptive algorithm employing the speed-accuracy trade-off concept to control our pediatric anklebot while delivering therapy for children with cerebral palsy.     

Choosing the fastest movement: perceiving speed-accuracy tradeoffs

Several studies have shown that humans exhibit an intimate knowledge of prospective motor actions when imagining and planning movements. To probe this knowledge, we used a 2-alternative forced-choice task to determine whether people are consistent with Fitts’s law when choosing the movement they perceive to require the least movement time. We hypothesized that participants would choose the target with the lower index of difficulty with a probability greater than 0.5 in all situations. Participants performed almost perfectly when one of the targets was closer, wider, or both. Contrary to expectations, however, participants showed biases for close targets when one of the targets was closer and narrower. We argue that this pattern of behavior may result from a subjective representation of movement time that is based on both Fitts’s law and the distance to the target, suggesting a preference for movements that are less effortful.     

Altered triggering of a prepared movement by a startling stimulus

An experiment is reported that investigated the effects of an auditory startling stimulus on a compound movement task. Previous findings have shown that, in a targeting task, a secondary movement can be initiated based on the proprioceptive information provided by a primary movement. Studies involving the presentation of a startling stimulus have shown that in reaction time (RT) tasks, prepared ballistic movements could be released early when participants are startled. In the present study we sought to determine whether the secondary component in an ongoing movement task, once prepared, could also be triggered by a startling stimulus. Participants performed a slow active elbow extension (22 degrees /s), opening their hand when the arm passed 55 degrees of extension from the starting point. An unexpected 124 dB startle stimulus was presented 5, 25, or 45 degrees into the movement. Findings showed that, when participants were startled, the secondary component was triggered despite incongruent kinesthetic information. However, this only occurred when the startle was presented late in the primary movement. This suggests that the secondary movement was not prepared prior to task initiation, but was "loaded" into lower brain structures at some point during the movement in preparation to be triggered by the CNS. This occurred late in the movement sequence, but >/=400 ms prior to reaching the target. These findings indicate that, in addition to ballistic RT tasks, a startle can be used to probe response preparation in ongoing compound movement tasks.     

DYSSYNCHRONOUS APRAXIA: FAILURE TO COMBINE SIMULTANEOUS PREPROGRAMMED MOVEMENTS

Limb apraxia, a defect in skilled, learned purposive movement, may be related to impairment of either representational or innervatory components of praxis processing. Innervatory motor patterns, in turn, may involve on-line motor programs (visual feedback-controlled) or prepared movement programs (independent of continuous visual feedback). We evaluated movement abilities ofthe innervatory pattern system in TB,a 26-year-old patient with apraxia from a left dorsolateral frontal stroke. TB and four controls performed nonmeaningful single and multi-joint movements to command, with multi-joint movements combined sequentially (e.g. "open and close your hand and then bend your elbow") or simultaneously (e.g. "open and close your hand; keep doing that while bending your elbow"). TB showed no difference between single-joint (71.5% correct) and multi-joint movements in sequential combinations (68% correct), but she was significantly worse at simultaneous movement combinations (28.6% correct; P < .02). Controls performed consistently at > 90% mean accuracy. TB and four normals also performed the Fitts (1954) task, in which they alternately tapped with a pen between two target circles of varying size. TB was proportionately slower than controls on the larger Fitts circles, which call predominantly on prepared movement programs; her performance on the smaller circles (involving more on-line programs) was comparable to normals. We conclude that functional synchrony of one innervatory pattern subtype, prepared movement programs, may require late-level frontal processing, and that failure at this level can result in both apraxia and defective programming of nonmeaningful movements.     

Dyssynchronous apraxia: failure to combine simultaneous preprogrammed movements

Limb apraxia, a defect in skilled, learned purposive movement, may be related to impairment of either representational or innervatory components of praxis processing. Innervatory motor patterns, in turn, may involve on-line motor programs (visual feedback-controlled) or prepared movement programs (independent of continuous visual feedback). We evaluated movement abilities ofthe innervatory pattern system in TB,a 26-year-old patient with apraxia from a left dorsolateral frontal stroke. TB and four controls performed nonmeaningful single and multi-joint movements to command, with multi-joint movements combined sequentially (e.g. "open and close your hand and then bend your elbow") or simultaneously (e.g. "open and close your hand; keep doing that while bending your elbow"). TB showed no difference between single-joint (71.5% correct) and multi-joint movements in sequential combinations (68% correct), but she was significantly worse at simultaneous movement combinations (28.6% correct; P < .02). Controls performed consistently at > 90% mean accuracy. TB and four normals also performed the Fitts (1954) task, in which they alternately tapped with a pen between two target circles of varying size. TB was proportionately slower than controls on the larger Fitts circles, which call predominantly on prepared movement programs; her performance on the smaller circles (involving more on-line programs) was comparable to normals. We conclude that functional synchrony of one innervatory pattern subtype, prepared movement programs, may require late-level frontal processing, and that failure at this level can result in both apraxia and defective programming of nonmeaningful movements.     

The organization of digit contact timing during grasping

While the process of hand preshaping during grasping has been studied for over a decade, there is relatively little information regarding the organization of digit contact timing (DCT). This dearth of information may be due to the assumption that DCT while grasping exhibits few regularities or to the difficulty in obtaining information through traditional movement recording techniques. In this study, we employed a novel technique to determine the time of digit contacts with the target object at a high precision rate in normal healthy participants. Our results indicate that, under our task conditions, subjects tend to employ a radial to ulnar pattern of DCT which may be modulated by the shape of the target object. Moreover, a number of parameters, such as the total contact time, the frequency of first contacts by the thumb and index fingers and the number of simultaneous contacts, are affected by the relative complexity of the target object. Our data support the notion that a great deal of information about the object’s physical features is obtained during the early moments of the grasp.     

Coordination between posture and movement: interaction between postural and accuracy constraints

We examined the interaction between the control of posture and an aiming movement. Balance control was varied by having subjects aim at a target from a seated or a standing position. The aiming difficulty was varied using a Fitts’-like paradigm (movement amplitude=30 cm; target widths=0.5, 1.0, 2.5 and 5 cm). For both postural conditions, all targets were within the reaching space in front of the subjects and kept at a fixed relative position with respect to the subjects’ body. Hence, for a given target size, the aiming was differentiated only by the postural context (seated vs. upright standing). For both postural conditions, movement time (MT) followed the well-known Fitts’ law, that is, it increased with a decreasing target size. For the smallest target width, however, the increased MT was greater when subjects were standing than when they were seated suggesting that the difficulty of the aiming task could not be determined solely by the target size. When standing, a coordination between the trunk and the arm was observed. Also, as the target size decreased, the center of pressure (CP) displacement increased without any increase in CP speed suggesting that the subjects were regulating their CP to provide a controlled referential to assist the hand movement. When seated, the CP kinematics was scaled with the hand movement kinematics. Increasing the index of difficulty led to a strong correlation between the hand speed and CP displacement and speed. The complex organization between posture and movement was revealed only by examining the specific interactions between speed–accuracy and postural constraints.     

Optimizing the control of high-ID movements: rethinking the power of the visual display

A recent experiment by Boyle et al. (Exp Brain Res 223:377–387, 2012a) demonstrated that providing a sine-wave template for participants to follow enhances performance and transfer on difficult (ID = 6) Fitts tasks. Another experiment (Fernandez and Bootsma in Acta Psychol 129:217–227, 2008) demonstrated the effectiveness of applying a nonlinear transformation of the visual feedback provided to participants executing difficult aiming movements. The present experiment was designed to determine whether these two enhancements when used together would provide further enhancements to difficult aiming movements. Participants were randomly assigned to one of the three acquisition conditions. Participants in the Fitts and Fitts_log condition were asked to flex/extend their arm in the horizontal plane at the elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. In the Sine_log condition, participants were asked to track a sine-wave pattern. The timing for Sine_log conditions was set to result in total times (movement time + dwell time) similar to that anticipated for the Fitts_log condition. The feedback displays for Fitts_log and Sine_log groups were subjected to a nonlinear transformation, but not for the Fitts group. Following 54 acquisition trials (17.5 s each) under their assigned condition, Test 1 was conducted under the same conditions as the participant experienced during the acquisition trials and Test 2 was conducted under Fitts conditions with the nonlinear transformation of the display data. Test 3 was conducted under typical Fitts conditions with no transformation of the display data. The results for Tests 1 and 2 indicated that total time and movement time for the Fitts_log and Sine_log groups were reduced relative to the Fitts condition. In addition, dwell time was significantly lower, a larger proportion of movement time was spent in the acceleration portion of the movement, and normalized peak velocity was significantly lower for the participants in the Sine_log condition than for participants in the Fitts_log condition. On Test 3, an untransformed Fitts condition was imposed; the Sine_log group outperformed the Fitts_log condition on all variables except hits, endpoint variability, and peak velocity where the Fitts_log and Sine_log groups performed similarly.     

The cost of moving with the left hand

Precise left-hand movements take longer than right-hand movements (for right-handers). To quantify how left-hand movements are affected by task difficulty and phase of movement control, we manipulated the difficulty of repetitive speeded aiming movements while participants used the left or right hand. We observed left-hand costs in both initial impulse and current control phases of movement. While left-hand cost during the initial impulse phase was small, left-hand cost during the current control phase varied from 10 to 60 ms, in direct proportion to the movement’s difficulty as quantified by Fitts’ law (0.77 < R ² < 0.99, across three experiments). In particular, in comparison with a difficult task for the right hand (Fitts’ ID_R = 6.6), the left hand’s task would have to be made easier by 0.5 bits (ID_L = 6.1) to be performed as quickly. The left-hand cost may reflect the time required for callosal transfer of information between the left and right hemispheres during the current control phase of precision left-hand movements or reflect movement control differences in the current control phase of movement that are inherent to the hemispheres. Overall, the present results support multiphase models of movement generation, in which separate specialized processes contribute to the launching and completion of precision hand movements.     

Timekeeping strategies operate independently from spatial and accuracy demands in beat-interception movements

The prevailing paradigm for researching sensorimotor synchronisation in humans involves finger tapping and temporal accuracy measures. However, many successful sensorimotor synchronisation actions require not only to be ‘in time’, but also to be in a predefined spatial position. Reaching this spatial position in many everyday actions often exceeds the average amplitude of a finger movement. The aim of this study is to address how people coordinate their movement to be in the right place at the right time when the scale of the movement varies. Does the scale of the movement and accuracy demands of the movement change the ability to accurately synchronise? To address these questions, a sensorimotor synchronisation task with three different inter-beat intervals, two different movement amplitudes and two different target widths was used. Our experiment demonstrated that people use different timing strategies—employing either a movement strategy (varying movement time) or a waiting strategy (keeping movement time constant) for large-scale movements. Those two strategies were found to be equally successful in terms of temporal accuracy and variability (spread of errors). With longer interval durations (2.5 and 3.5 s), variability of sensorimotor synchronisation performance increased (measured as the spread of errors). Analysing the data using the Vorberg and Wing (Handbook of perception and action. Academic Press, New York, pp 181–262, 1996) model shows a need to develop further existing timing models of sensorimotor synchronisation so that they could apply to large-scale movements, where different movement strategies naturally emerge.     

Effects of postural task requirements on the speed–accuracy trade-off

We investigated the speed–accuracy trade-off in a task of pointing with the big toe of the right foot by a standing person that was designed to accentuate the importance of postural adjustments. This was done to test two hypotheses: (1) movement time during foot pointing will scale linearly with ID during target width changes, but the scaling will differ across movement distances; and (2) variations in movement time will be reflected in postural preparations to foot motion. Ten healthy adults stood on the force plate and were instructed to point with the big toe of the right foot at a target (with widths varying from 2 to 10 cm) placed on the floor in front of the subject at a distance varying from 10 to 100 cm. The instruction given to the subjects was typical for Fitts’ paradigm: “be as fast and as accurate as possible in your pointing movement”. The results have shown that movement time during foot pointing movements scaled with both target distance (D) and target width (W), but the two dependences could not be reduced to a single function of W/D, confirming the first hypothesis. With respect to the second hypothesis, we found that changes in task parameters led to proportional variations in movement speed and indices of variability of the postural adjustments prior to leg movement initiation, confirming the second hypothesis. Both groups of observations were valid over the whole range of distances despite the switch of the movement strategy in the middle of this range. We conclude that the speed–accuracy trade-off in a task with postural adjustments originates at the level of movement planning. The different dependences of movement time on D and W may be related to spontaneous postural sway (migration of the point of application of the resultant force acting on the body of the standing person). The results may have practical implications for posture and gait rehabilitation techniques that use modifications of stepping accuracy.     

Inverse relationship between task complexity and performance deficit in 5 m water immersion

Previous research on cognitive deficits during shallow water immersion led to inconsistent results: some authors observed deficits at 5 m, but others only at depths well beyond 5 m. The present study evaluates whether this discrepancy could be related to different levels of difficulty. Forty-eight subjects participated in a mental rotation task and in a color-word task, both having multiple levels of difficulty. The two tasks were administered once 5 m below the water’s surface and once on dry land. Compared to land, subjects’ reaction time increased in 5 m depth when task difficulty was low, but it did not increase when task difficulty was high. Thus, performance deficits in 5 m depth were inversely related to task complexity. We interpret this counter-intuitive finding within the framework of a multiple-channel parallel processing model, with channels that are differentially sensitive to immersion. This model correctly predicts performance deficits on simple, but not on complex skills at smaller depths, and deficits on simple as well as complex skills at larger depths, in accordance with the present findings and data from literature.     

Manipulating time-to-plan alters patterns of brain activation during the Fitts’ task

Fitts’ law predicts that there is an essential trade-off between speed and accuracy during movement. Past investigations of Fitts’ law have not characterized whether advance planning of upcoming fast and accurate movements impacts either behavior or patterns of brain activation. With an event-related functional magnetic resonance imaging (fMRI) paradigm, we investigated the neural correlates of advance planning and movement difficulty of rapid, goal-directed aimed movements using a discrete version of the classic Fitts’ task. Our behavioral data revealed strong differences in response time, initial movement velocity, and end-point accuracy based on manipulation of both time to plan movements and response difficulty. We discovered a modulation of the neural network associated with executing the Fitts’ task that was dependent on the availability of time to plan the upcoming movement and motor difficulty. Specifically, when time to plan for the upcoming movement was available, medial frontal gyrus (BA 10), pre-SMA (BA 6), putamen and cerebellar lobule VI were uniquely active to plan movements. Further, their activation correlated with behavioral measures of movement. In contrast, manipulating movement difficulty invoked a different pattern of brain activations in regions that are known to participate in motor control, including supplementary motor area (BA 6), sensory motor cortex (BA 4, 3, 2) and putamen. Our finding that medial frontal gyrus (BA 10) was important for discrete, fast and accurate movements expands the known role of this brain region, which in the past has been identified as a cognitive processing system supporting stimulus-oriented attending. We now extend this conceptualization to include motor functions such as those employed for processing for rapid, goal-directed aimed movements.

Context influences on the preparation and execution of reaching movements

The ability of rapidly adapting our motor behaviour in order to face the unpredictable changes in the surrounding environment is fundamental for survival. To achieve such a high level of efficiency our motor system has to assess continuously the context in which it acts, gathering all available information that can be relevant for planning goal-oriented movements. One still-debated aspect of movement organization is the nature and timing of motor planning. While motor plans are often taken to be concerned with the setting of kinematic parameters as a function of perceptual and motor factors, it has been suggested that higher level, cognitive factors may also affect planning. To explore this issue further, we asked 18 right-handed human participants to perform speeded hand-reaching movement toward a visual target in two different experimental settings, a reaction time (RT) paradigm (go-only task) and a countermanding paradigm. In both tasks participants executed the same movements, but in the countermanding task no-stop trials were randomly intermixed with stop trials. In stop trials participants were required to withhold the ongoing movement whenever a stop signal was shown. It is known that the presence of stop trials induces a consistent increase of the RTs of no-stop trials with respect to the RTs of go-only trials. However, nothing is known about a similar effect for movement times (MTs). We found that RTs and MTs exhibit opposing tendencies, so that a decrease in the RT correspond to an increase in the MT and vice versa. This tendency was present in all our participants and significant in 90% of them. Furthermore we found a moderate, but again very consistent, anticorrelation between RTs and MTs on a trial-by-trial base. These findings are consistent with strategic changes in movement programmes for the very same movements under different cognitive contexts, requiring different degrees of feedback-driven control during movement.     

Context influences on the preparation and execution of reaching movements

The ability of rapidly adapting our motor behaviour in order to face the unpredictable changes in the surrounding environment is fundamental for survival. To achieve such a high level of efficiency our motor system has to assess continuously the context in which it acts, gathering all available information that can be relevant for planning goal-oriented movements. One still-debated aspect of movement organization is the nature and timing of motor planning. While motor plans are often taken to be concerned with the setting of kinematic parameters as a function of perceptual and motor factors, it has been suggested that higher level, cognitive factors may also affect planning. To explore this issue further, we asked 18 right-handed human participants to perform speeded hand-reaching movement toward a visual target in two different experimental settings, a reaction time (RT) paradigm (go-only task) and a countermanding paradigm. In both tasks participants executed the same movements, but in the countermanding task no-stop trials were randomly intermixed with stop trials. In stop trials participants were required to withhold the ongoing movement whenever a stop signal was shown. It is known that the presence of stop trials induces a consistent increase of the RTs of no-stop trials with respect to the RTs of go-only trials. However, nothing is known about a similar effect for movement times (MTs). We found that RTs and MTs exhibit opposing tendencies, so that a decrease in the RT correspond to an increase in the MT and vice versa. This tendency was present in all our participants and significant in 90% of them. Furthermore we found a moderate, but again very consistent, anticorrelation between RTs and MTs on a trial-by-trial base. These findings are consistent with strategic changes in movement programmes for the very same movements under different cognitive contexts, requiring different degrees of feedback-driven control during movement.     

The Flexible Item Selection Task (FIST): A Measure of Executive Function in Preschoolers

Abstraction and cognitive flexibility were assessed in 197 preschool children at 2, 3, 4, and 5 years of age using the Flexible Item Selection Task, a task adapted from the Visual-Verbal Test (Feldman & Drasgow, 1951). On this new inductive task, children were shown a set of 3 cards and required to select 2 cards that matched each other on 1 dimension (Selection 1) and then to select a different pair of cards that matched each other on another dimension (Selection 2). Thus, 1 of the 3 cards always had to be selected twice according to different dimensions. Two-year-olds failed to understand basic task requirements as assessed by a criterial measure. Three-year-olds did more poorly on Selection 1 than 4- and 5-year-olds (who performed near ceiling), suggesting that 3-year-olds had difficulty with the abstraction component of the task. Four-year-olds did worse than 5-year-olds on Selection 2, suggesting that they had difficulty with the cognitive flexibility component (i.e., difficulty selecting the same card on more than 1 dimension). Results are discussed in terms of the development of executive function.     

“Self pop-out”: agency enhances self-recognition in visual search

In real-life situations, we are often required to recognize our own movements among movements originating from other people. In social situations, these movements are often correlated (for example, when dancing or walking with others) adding considerable difficulty to self-recognition. Studies from visual search have shown that visual attention can selectively highlight specific features to make them more salient. Here, we used a novel visual search task employing virtual reality and motion tracking to test whether visual attention can use efferent information to enhance self-recognition of one’s movements among four or six moving avatars. Active movements compared to passive movements allowed faster recognition of the avatar moving like the subject. Critically, search slopes were flat for the active condition but increased for passive movements, suggesting efficient search for active movements. In a second experiment, we tested the effects of using the participants’ own movements temporally delayed as distractors in a self-recognition discrimination task. We replicated the results of the first experiment with more rapid self-recognition during active trials. Importantly, temporally delayed distractors increased reaction times despite being more perceptually different than the spatial distractors. The findings demonstrate the importance of agency in self-recognition and self-other discrimination from movement in social settings.     

The effect of haptic guidance and visual feedback on learning a complex tennis task

While haptic guidance can improve ongoing performance of a motor task, several studies have found that it ultimately impairs motor learning. However, some recent studies suggest that the haptic demonstration of optimal timing, rather than movement magnitude, enhances learning in subjects trained with haptic guidance. Timing of an action plays a crucial role in the proper accomplishment of many motor skills, such as hitting a moving object (discrete timing task) or learning a velocity profile (time-critical tracking task). The aim of the present study is to evaluate which feedback conditions—visual or haptic guidance—optimize learning of the discrete and continuous elements of a timing task. The experiment consisted in performing a fast tennis forehand stroke in a virtual environment. A tendon-based parallel robot connected to the end of a racket was used to apply haptic guidance during training. In two different experiments, we evaluated which feedback condition was more adequate for learning: (1) a time-dependent discrete task—learning to start a tennis stroke and (2) a tracking task—learning to follow a velocity profile. The effect that the task difficulty and subject’s initial skill level have on the selection of the optimal training condition was further evaluated. Results showed that the training condition that maximizes learning of the discrete time-dependent motor task depends on the subjects’ initial skill level. Haptic guidance was especially suitable for less-skilled subjects and in especially difficult discrete tasks, while visual feedback seems to benefit more skilled subjects. Additionally, haptic guidance seemed to promote learning in a time-critical tracking task, while visual feedback tended to deteriorate the performance independently of the task difficulty and subjects’ initial skill level. Haptic guidance outperformed visual feedback, although additional studies are needed to further analyze the effect of other types of feedback visualization on motor learning of time-critical tasks.