Discrete Movement Sequences Research Articles

Explaining the neural activity distribution associated with discrete movement sequences: Evidence for parallel functional systems

To explore the effects of practice we scanned participants with fMRI while they were performing four-key unfamiliar and familiar sequences, and compared the associated activities relative to simple control sequences. On the basis of a recent cognitive model of sequential motor behavior (C-SMB), we propose that the observed neural activity would be associated with three functional networks that can operate in parallel and that allow (a) responding to stimuli in a reaction mode, (b) sequence execution using spatial sequence representations in a central-symbolic mode, and (c) sequence execution using motor chunk representations in a chunking mode. On the basis of this model and findings in the literature, we predicted which neural areas would be active during execution of the unfamiliar and familiar keying sequences. The observed neural activities were largely in line with our predictions, and allowed functions to be attributed to the active brain areas that fit the three above functional systems. The results corroborate C-SMB’s assumption that at advanced skill levels the systems executing motor chunks and translating key-specific stimuli are racing to trigger individual responses. They further support recent behavioral indications that spatial sequence representations continue to be used.

High-Intensity Aerobic Exercise Enhances Motor Memory Retrieval.

In previous work, acute high-intensity aerobic exercise benefited continuous motor sequence task learning. As memory processes underlying motor sequence learning vary between tasks involving continuous and discrete movements, the objective of the current study was to determine whether the beneficial effects of acute aerobic exercise generalize to the learning of a discrete motor sequence task. Sixteen young healthy individuals practiced a discrete motor sequence task preceded by either a period of rest or a bout of high-intensity cycling. Participants moved a cursor with a computer mouse to a series of discretely presented targets on a screen. Target presentation followed either a repeated or a random sequence, which allowed the evaluation of implicit sequence-specific motor learning. The change in movement response time over practice (△-ACQ) and from practice to a 24-h "no-exercise" retention test (△-RET) and the rate of improvement over practice (α-ACQ) and during the retention test (α-RET) were calculated. α-RET was greater for the repeated sequence than random sequences after aerobic exercise (P = 0.01), but not rest (P = 0.33). Further, α-RET for the repeated sequence was greater after aerobic exercise than for either sequence (repeated, random) in the rest condition (P ≤ 0.01). There were no differences between sequences and/or conditions for △-ACQ, △-RET, or α-RET (P ≥ 0.57). Our findings show a positive effect of acute high-intensity aerobic exercise on implicit discrete motor sequence learning. Performing exercise before practice increased the rate of improvement at a 24-h delayed retention test, suggesting an effect on the rate of motor memory retrieval. Pairing acute aerobic exercise with motor practice may facilitate learning of discrete movement sequences in sport or rehabilitation settings.

Cognitive and neural foundations of discrete sequence skill: A TMS study

Executing discrete movement sequences typically involves a shift with practice from a relatively slow, stimulus-based mode to a fast mode in which performance is based on retrieving and executing entire motor chunks. The dual processor model explains the performance of (skilled) discrete key-press sequences in terms of an interplay between a cognitive processor and a motor system. In the present study, we tested and confirmed the core assumptions of this model at the behavioral level. In addition, we explored the involvement of the pre-supplementary motor area (pre-SMA) in discrete sequence skill by applying inhibitory 20min 1-Hz off-line repetitive transcranial magnetic stimulation (rTMS). Based on previous work, we predicted pre-SMA involvement in the selection/initiation of motor chunks, and this was confirmed by our results. The pre-SMA was further observed to be more involved in more complex than in simpler sequences, while no evidence was found for pre-SMA involvement in direct stimulus–response translations or associative learning processes. In conclusion, support is provided for the dual processor model, and for pre-SMA involvement in the initiation of motor chunks.

Post-error slowing in sequential action: an aging study

Previous studies demonstrated significant differences in the learning and performance of discrete movement sequences across the lifespan: Young adults (18–28 years) showed more indications for the development of (implicit) motor chunks and explicit sequence knowledge than middle-aged (55–62 years; Verwey et al., 2011) and elderly participants (75–88 years; Verwey, 2010). Still, even in the absence of indications for motor chunks, the middle-aged and elderly participants showed some performance improvement too. This was attributed to a sequence learning mechanism in which individual reactions are primed by implicit sequential knowledge. The present work further examined sequential movement skill across these age groups. We explored the consequences of making an error on the execution of a subsequent sequence, and investigated whether this is modulated by aging. To that end, we re-analyzed the data from our previous studies. Results demonstrate that sequencing performance is slowed after an error has been made in the previous sequence. Importantly, for young adults and middle-aged participants the observed slowing was also accompanied by increased accuracy after an error. We suggest that slowing in these age groups involves both functional and non-functional components, while slowing in elderly participants is non-functional. Moreover, using action sequences (instead of single key-presses) may allow to better track the effects on performance of making an error.

A Discrete Movement Model for Cursor Tracking Validated in the Context of a Dual-Task Experiment

Understanding human cursor tracking behavior is essential in understanding human motor control. Though tracking has been hypothesized as a sequence of discrete movements, better data is needed to support the theory. By analyzing moment-to-moment tracking data, this paper shows that discrete, non-ballistic movements exist throughout a tracking task, and that these short submovements can be characterized by either Fitts’ law or a linear model. A cognitive model was built to incorporate the characteristics of these discrete movements into a dual task. Using parameters estimated through linear regression of the movement data, the model achieves a good fit to the overall performance measures of the dual-task experiment. This research investigates the characteristics of human motor control in tracking tasks, improves modeling techniques by providing a new method for estimating tracking parameters, and advances the science of motor control with new evidence for the discrete movement tracking hypothesis. The discrete movement model presented here offers an excellent alternative to established control theory models that are used to simulate steering in cognitive models of driving.

Directed corticocortical functional connectivity at the early stages of serial learning in adults and seven- to eight-year-old children

Serial learning at its earlier stages, presumably involving the working memory, was studied in adults and seven- to eight-year-old children during the reproduction of a sequence of discrete movements following the order specified by a sequence of visual stimuli. In both age groups, the learning curves (latent time vs. trial number) were qualitatively similar in shape. The overall shape of the learning curve depended on the relative proportion of the fast vs. slow phases of latent time reduction. Comparison of the corticocortical functional connectivity patterns in the prestimulus period in the sequence reproduction task vs. the simple visuomotor reaction task showed a general tendency of an increase in the influence of postcentral cortical areas accompanied by the reduced influence of prefrontal and central cortical areas. In particular, it was typical of adults to show an increase in the directed influence of temporo-parieto-occipital (TPO) cortical areas, while the children also showed an increase in the directed influence of the parietal cortex. Comparison of the subgroups with different shapes of learning curves in the prestimulus period has shown the difference in their patterns of directed functional connectivity. The results are discussed with a special emphasis on the role of the working memory retaining the internal representations of sequences being learned.

Optimal Control of a Hybrid Rhythmic-Discrete Task: The Bouncing Ball Revisited

Rhythmically bouncing a ball with a racket is a hybrid task that combines continuous rhythmic actuation of the racket with the control of discrete impact events between racket and ball. This study presents experimental data and a two-layered modeling framework that explicitly addresses the hybrid nature of control: a first discrete layer calculates the state to reach at impact and the second continuous layer smoothly drives the racket to this desired state, based on optimality principles. The testbed for this hybrid model is task performance at a range of increasingly slower tempos. When slowing the rhythm of the bouncing actions, the continuous cycles become separated into a sequence of discrete movements interspersed by dwell times and directed to achieve the desired impact. Analyses of human performance show increasing variability of performance measures with slower tempi, associated with a change in racket trajectories from approximately sinusoidal to less symmetrical velocity profiles. Matching results of model simulations give support to a hybrid control model based on optimality, and therefore suggest that optimality principles are applicable to the sensorimotor control of complex movements such as ball bouncing.

On rhythmic and discrete movements: reflections, definitions and implications for motor control

At present, rhythmic and discrete movements are investigated by largely distinct research communities using different experimental paradigms and theoretical constructs. As these two classes of movements are tightly interlinked in everyday behavior, a common theoretical foundation spanning across these two types of movements would be valuable. Furthermore, it has been argued that these two movement types may constitute primitives for more complex behavior. The goal of this paper is to develop a rigorous taxonomic foundation that not only permits better communication between different research communities, but also helps in defining movement types in experimental design and thereby clarifies fundamental questions about primitives in motor control. We propose formal definitions for discrete and rhythmic movements, analyze some of their variants, and discuss the application of a smoothness measure to both types that enables quantification of discreteness and rhythmicity. Central to the definition of discrete movement is their separation by postures. Based on this intuitive definition, certain variants of rhythmic movement are indistinguishable from a sequence of discrete movements, reflecting an ongoing debate in the motor neuroscience literature. Conversely, there exist rhythmic movements that cannot be composed of a sequence of discrete movements. As such, this taxonomy may provide a language for studying more complex behaviors in a principled fashion.

Biomechanical and perceptual determinants of drawing angles

This study focuses on perceptual and biomechanical determinants of the kinematics of angular drawing movements. Two experiments are reported in which twelve righthanded adults were asked to draw geometrical patterns consisting of three segments comprising either two acute or two obtuse angles. In Experiment 1, a lower frequency of pauses was observed in acute patterns and their segment length tended to be overestimated. The former effect is attributed to the exploitation of elasticity (Guiard, 1993). In order to evaluate whether the latter effect was due to perceptual factors, a second experiment was conducted. Twelve subjects drew a a subset of the angular patterns under normal visual conditions and under conditions in which they could neither see their moving limb nor the resulting drawing trace. Again, subjects produced more pauses at obtuse than at acute angles and tended to overestimate the segment length in acute patterns. It is concluded that pauses are likely to occur between segments of discrete movement sequences when potential energy needs to be dissipated. When conditions arise that allow subjects to exploit elasticity, however, segment length tends to increase. The results of Experiment 2 confirm that these phenomena are independent from visual perception.

Proprioceptive coordination of discrete movement sequences: mechanism and generality

A "discrete" movement sequence is defined as a movement with a single goal that involves a series of overlapping joint rotations. Reaching-and-grasping and throwing are examples of discrete movement sequences. The central nervous system (CNS) can use reafferent proprioceptive information from one joint rotation in a sequence to coordinate subsequent rotations at other joints. The experiments reported in this paper demonstrate how the human CNS uses proprioceptive information to coordinate discrete movement sequences. We examined the mechanism (at an information processing level) underlying proprioceptive coordination and the generality (i.e., the boundary conditions) of these mechanisms as they apply to everyday movement sequences. Adult human subjects performed a discrete movement sequence that resembles backhand throwing: elbow extension followed by hand opening. The task was to open the hand as the elbow passed through a prescribed "target" angle. We eliminated visual information and made the arrival time at the target angle unpredictable so that the available kinematic information was provided exclusively by proprioception. The subjects were capable of performing this motor task with a high degree of precision, thereby demonstrating that the nervous system can use proprioceptive input to coordinate discrete movement sequences. Our data indicate that precise coordination is achieved by extracting kinematic information related to both the velocity of elbow rotation as well as the elbow position during movement (i.e., "dynamic position"). Dynamic position information appears to be encoded as both absolute joint angle and angular distance, although more precisely as angular distance. Although our experiments were conducted under rather restrictive laboratory conditions, this mechanism of motor coordination might also apply to everyday movement. Our results suggest that this mechanism could be employed for passive as well as active movement sequences, with and without opposing loads; it could exert its influence in discrete movement sequences as brief as 210 ms or as long as 1.5 s; and it does not involve any significant degree of learning (this proprioceptive mechanism appears to be readily available for use on the first attempt of a novel motor task).