Evidence of Common Timing Processes in the Control of Manual,Orofacial, and Speech Movements

Recent investigations of timing in motor control have been interpreted as support for the concept of brain modularity. According to this concept, the brain is organized into functional modules that contain mechanisms responsible for general processes. Keele and colleagues (Keele & Hawkins, 1982; Keele & Ivry, 1987; Keele, Ivry, & Pokorny, 1987; Keele, Pokorny, Corcos, & Ivry, 1985) demonstrated that the within-subject variability in cycle duration of repetitive movements is correlated across finger, forearm, and foot movements, providing evidence in support of a general timing module. The present study examines the notion of timing modularity of speech and nonspeech movements of the oral motor system as well as the manual motor system. Subjects produced repetitive movements with the finger, forearm, and jaw. In addition, a fourth task involved the repetition of a syllable. All tasks were to be produced with a 400-ms cycle duration; target duration was established with a pacing tone, which then was removed. For each task, the within-subject variability of the cycle duration was computed for the unpaced movements over 20 trials. Significant correlations were found between each pair of effectors and tasks. The present results provide evidence that common timing processes are involved not only in movements of the limbs, but also in speech and nonspeech movements of oral structures.     

Timing and the Control of Rhythmic Upper-Limb Movements

Accurate timing of limb displacement is crucial for effective motor control. The authors examined the effects of movement velocity, duration, direction, added mass, and auditory cueing on timing, spatial, and trajectory variability of single- and multijoint rhythmic movements. During single-joint movements, increased velocity decreased timing and spatial variability, whereas increased movement duration increased timing variability but decreased spatial variability. For multijoint movements, regardless of condition, increasing velocity decreased joint timing, spatial, and trajectory variability, but all hand variabilities were unaffected by velocity, duration, load, or direction. Timing, spatial, and trajectory variability was greater at the shoulder compared with the elbow and minimal at the hand, supporting the notion that reaching movements are planned in hand space as opposed to joint space.     

Planning of Reach-and-Grasp Movements: Effects of Validity and Type of Object Information

Individuals are assumed to plan reach-and-grasp movements by using two separate processes. In 1 of the processes, extrinsic (direction, distance) object information is used in planning the movement of the arm that transports the hand to the target location (transport planning); whereas in the other, intrinsic (shape) object information is used in planning the preshaping of the hand and the grasping of the target object (manipulation planning) In 2 experiments, the authors used primes to provide information to participants (N = 5, Experiment 1; N = 6, Experiment 2) about extrinsic and intrinsic object properties. The validity of the prime information was systematically varied. The primes were succeeded by a cue, which always correctly identified the location and shape of the target object. Reaction times were recorded. Four models of transport and manipulation planning were tested. The only model that was consistent with the data was 1 in which arm transport and object manipulation planning were postulated to be independent processes that operate partially in parallel. The authors suggest that the processes involved in motor planning before execution are primarily concerned with the geometric aspects of the upcoming movement but not with the temporal details of its execution.     

Temporal Precision in Tapping and Circle Drawing Movements at Preferred Rates is Not Correlated: Further Evidence Against Timing as a General-Purpose Ability

Recently, researchers have discovered that individuals who are consistent timers in a tapping task are not necessarily consistent timers when they perform a continuous drawing task. In other words, nonsignificant correlations were found among tapping and drawing movements for timing precision (S. D. Robertson et al., 1999). In the present experiment, the authors investigated whether or not consistency in timing for tapping and drawing was correlated when participants (N = 24) were allowed to move at their preferred rate of movement. There were no significant correlations between tapping and drawing in terms of timing precision. That result lends further support to the notion that timing behavior is specific to the nature of the task, and thus further weakens the idea that timing is a generalized ability that can be imposed on a variety of different types of tasks.     

Effects of an Auditory Model on the Learning of Relative and Absolute Timing

The effects of an auditory model on the learning of relative and absolute timing were examined. In 2 experiments, participants attempted to learn to produce a 1,000- or 1,600-ms sequence of 5 key presses with a specific relative-timing pattern. In each experiment, participants were, or were not, provided an auditory model that consisted of a series of tones that were temporally spaced according to the criterion relative-timing pattern. In Experiment 1, participants (n = 14) given the auditory template exhibited better relative- and absolute-timing performance than participants (n = 14) not given the auditory template. In Experiment 2, auditory and no-auditory template groups again were tested, but in that experiment each physical practice participant (n = 16) was paired during acquisition with an observer (n = 16). The observer was privy to all instructions as well as auditory and visual information that was provided the physical practice participant. The results replicated the results of Experiment 1: Relative-timing information was enhanced by the auditory template for both the physical and observation practice participants. Absolute timing was improved only when the auditory model was coupled with physical practice. Consistent with the proposal of D. M. Scully and K. M. Newell (1985), modeled timing information in physical and observational practice benefited the learning of the relative-timing features of the task, but physical practice was required to enhance absolute timing.     

Rapid Error Correction During Human Arm Movements

Studies were made of rapid error correction movements in eight subjects performing a visually guided tracking task involving flexion-extension movements about the elbow. Subjects were required to minimize reaction times in this two-choice task. Errors in initial movement direction occurred in about 3% of the trials. Error correction times (time from initiation to reversal of movement in incorrect direction) ranged from 30-150 ms. The first sign of correction of the error movement was a suppression of the electromyographic (EMG) activity in the muscle producing the error movement. This suppression started as early as 20-40 ms after the initiation of the error-related EMG activity and as much as 50 ms before any overt sign of limb movement. The correction of the error movement was also accompanied by an increase in the drive to the muscle which moved the arm in the correct direction. This increased activity always occurred after the initiation of the error movement. It is concluded that the first step in the error correction, suppression of drive to the muscle producing the error movement, cannot be based on information from the moving limb. It is thus suggested that this earliest response to the error movement is based on central monitoring of the commands for movement.     

Haptic Guidance Can Enhance Motor Learning of a Steering Task

Haptic guidance can improve the immediate performance of a motor task by enforcing a desired pattern of kinematics, but several studies have found that it impairs motor learning. In this study, we studied whether guidance from a robotic steering wheel can improve one's short-term learning of steering a simulated vehicle. We developed a computer algorithm that adapted the firmness of the guidance based on ongoing error. Training with "guidance-as-needed" or "fixed guidance" allowed participants to learn to steer without experiencing large errors and produced slightly better immediate retention than did training without guidance, apparently because participants were better able to learn when to initiate turns. Training with guidance-as-needed produced slightly better results than training with fixed guidance: the guidance-as-needed participants' errors were significantly smaller when guidance was removed. However, this difference quickly dissipated with more practice. We conclude that haptic guidance can benefit short-term learning of a steering-type task while also limiting performance errors during training.     

Contextual Interference in Movements of the Same Class: Differential Effects on Program and Parameter Learning

Contextual interference effects in motor learning usually were not found when the tasks to be learned presumably required the same generalized motor program (GMP) and differed only with regard to the movement parameters (see Lee, Wulf, & Schmidt, 1992; Magill & Hall, 1990). Thus, tasks requiring different motor programs (e.g., different relative timings) seemed to be a prerequisite for random practice to be more effective than blocked practice. However, the previous studies (that did not find random/blocked differences) used global error measures that confounded errors in relative timing and errors in absolute timing. In the present study, subjects practiced three movement patterns that had the same relative timing (requiring the same GMP) but different overall durations (requiring different parameters). Errors in relative timing and in absolute timing were assessed separately. The results indicate that random practice is more effective for the learning of relative timing (GMP learning) and less effective for the learning of absolute timing (parameter learning) than blocked practice. Preliminary ideas as to the reasons for this effect are discussed.     

Motor Programming When Sequencing Multiple Elements of the Same Duration

Motor programming at the self-select paradigm was adopted in 2 experiments to examine the processing demands of independent processes. One process (INT) is responsible for organizing the internal features of the individual elements in a movement (e.g., response duration). The 2nd process (SEQ) is responsible for placing the elements into the proper serial order before execution. Participants in Experiment 1 performed tasks involving 1 key press or sequences of 4 key presses of the same duration. Implementing INT and SEQ was more time consuming for key-pressing sequences than for single key-press tasks. Experiment 2 examined whether the INT costs resulting from the increase in sequence length observed in Experiment 1 resulted from independent planning of each sequence element or via a separate "multiplier" process that handled repetitions of elements of the same duration. Findings from Experiment 2, in which participants performed single key presses or double or triple key sequences of the same duration, suggested that INT is involved with the independent organization of each element contained in the sequence. Researchers offer an elaboration of the 2-process account of motor programming to incorporate the present findings and the findings from other recent sequence-learning research.     

Concurrent Directional Adaptation of Reactive Saccades and Hand Movements to Target Displacements of Different Size

When eye and hand movements are concurrently aimed at double-step targets that call for equal and opposite changes of response direction (–10° for the eyes, +10° for the hand), adaptive recalibration of both motor systems is strongly attenuated; instead, hand but not eye movements are changed by corrective strategies (V. Grigorova et al., 2013a). The authors introduce a complementary paradigm, where double-step targets call for a –10° change of eye and a ?30° change for hand movements. If compared to control subjects adapting only the eyes or only the hand, adaptive improvements were comparable for the eyes but were twice as large for the hand; in contrast, eye and hand aftereffects were comparable to those in control subjects. The authors concluded that concurrent exposure of eyes and hand to steps of the same direction but different size facilitated hand strategies, but didn't affect recalibration. This finding together with previous one (V. Grigorova et al., 2013a), suggests that concurrent adaptation of eyes and hand reveals different mechanisms of recalibration for step sign and step size, which are shared by reactive saccades and hand movements. However, hand mostly benefits from strategies provoked by the difference in target step sign and size.     

Utility Functions: A Compromise Programming Approach to Specification and Optimization

Nowadays, utility theory and compromise programming (CP) are considered very different paradigms and methodologies to measure preferences as well as to determine decision maker's optima on an efficient frontier. In this paper, however, we show that a utility function with separate variables (presented in the form of a Taylor series around the ideal point) is reducible to a weighted sum of CP distances. This linkage between utility and compromise (based on a main assumption in which the usual utility functions hold) leads to (i) a method for specification and optimization of usual utility functions by operational technique and (ii) a reformulation of standard CP with the advantage of determining the best CP solution from a utility perspective. © 1997 John Wiley & Sons, Ltd.     

Visual Feedback and Positioning Movements

Subjects (n = 60) performed both the reproduction and learning of a linear positioning movement under one of five visual feedback conditions. Results from two experiments indicated that visual cues from the task display augmented information available from visual feedback of the movement per se. Extraneous cues from the task display have clearly confounded the manipulation of visual feedback in previous positioning studies. When these cues are eliminated, visual distance information seems more useful than visual location information.     

On the Role of Visual Afferent Information for the Control of Aiming Movements Toward Targets of Different Sizes

The authors investigated (a) whether the specificity of practice hypothesis is mediated by the importance of visual afferent information for the control of manual aiming movements and (b) how movement planning and online correction processes to the movement initial impulse are affected by the withdrawal of visual information in transfer. In acquisition, participants (N = 40) aimed at targets of different sizes in a full-vision or in a target-only condition before being transferred to a target-only condition without knowledge of results. The results supported the hypothesis that learning is specific to the source or sources of afferent information that are more likely to ensure optimal performance. The results also suggested that individuals will not always use visual afferent information more extensively when aiming at a small rather than at a large target. Instead, in a temporally constrained task, the relative efficiency of visually based corrections appears to mediate how exclusively an individual will rely on online visual afferent information for movement control. Finally, the detailed kinematic analysis performed in the present study clearly indicated that online modifications to the movement primary impulse are possible, arguing for a continuous or pseudo-continuous control of relatively slow aiming movements on the basis of visual afferent input.     

Timing Precision in Circle Drawing Does Not Depend on Spatial Precision of the Timing Target

The authors manipulated the width of a timing target in continuous circle drawing to determine whether a more stringent spatial-timing criterion would produce an increase in participants' (N = 30) temporal variability. They also examined the effect of the computational method of determining cycle duration. There was no effect of spatial precision on temporal variability in circle drawing, and tapping and circle drawing were found to use the same criterion. Those findings lend strong support to the earlier view of R. B. Ivry, R. M. Spencer, H. N. Zelaznik, and J. Diedrichsen (2002), who argued that continuous tasks such as circle drawing are timed differently from discrete-like tasks such as tapping. Therefore, the results of the present study provide support for the event and emergent timing frameworks.     

Anticipatory Planning of Sequential Hand and Finger Movements

ABSTRACT

Hand movements may be anticipatorily planned to reach an immediate target and at the same time facilitate movements to subsequent targets. Researchers have proposed that in anticipatory planning, information about subsequent targets needs to be processed to engage in the planning of the next movement. To test this hypothesis, the authors varied the information 48 participants had about to-be-executed two-step hand and finger movement sequences prior to a choice reaction signal. Movements were initialized faster if participants had advance information about the second target of the sequence than if participants had no advance information at all. The results imply that movement segments to late targets in a movement sequence may be at least partially planned, even if information about earlier targets is not yet available.     

Development of sensorimotor synchronization abilities: Motor and cognitive components

The aim of the present study was to examine both the development of sensorimotor synchronization in children in the age range from 5 to 8 years and the involvement of motor and cognitive capacities. Children performed a spontaneous motor tempo task and a synchronization–continuation task using an external auditory stimulus presented at three different inter-stimulus intervals: 500, 700, and 900 ms. Their motor and cognitive abilities (short-term memory, working memory, and attention) were also assessed with various neuropsychological tests. The results showed some developmental changes in synchronization capacities, with the regularity of tapping and the ability to slow down the tapping rate improving with age. The age-related differences in tapping were nevertheless greater in the continuation phase than in the synchronization phase. In addition, the development of motor capacities explained the age-related changes in performance for the synchronization phase and the continuation phase, although working memory capacities were also involved in the interindividual differences in performance in the continuation phase. The continuation phase is thus more cognitively demanding than the synchronization phase. Consequently, the improvement in sensorimotor synchronization during childhood is related to motor development in the case of synchronization but also to cognitive development with regard to the reproduction and maintenance of the rhythm in memory.     

Weber (Slope) Analyses of Timing Variability in Tapping and Drawing Tasks

Timing variability in continuous drawing tasks has not been found to be correlated with timing variability in repetitive finger tapping in recent studies (S. D. Robertson et al., 1999; H. N. Zelaznik, R. M. C. Spencer, & R. B. Ivry, 2002). Furthermore, the central component of timing variability, as measured by the slope of the timing variance versus the square of the timed interval, differed for tapping and drawing tasks. On the basis of those results, the authors posited that timing in tapping is explicit and as such uses a central representation of the interval to be timed, whereas timing in drawing tasks is implicit, that is, the temporal component is an emergent property of the trajectory produced. The authors examined that hypothesis in the present study by determining the linear relationship between timing variance and squared duration for tapping, circle-drawing, and line-drawing tasks. Participants (N = 501 performed 1 of 5 tasks: finger tapping, line drawing in the x dimension, line drawing in the y dimension, continuous circle drawing timed in the x dimension, or continuous circle drawing timed in the y dimension. The slopes differed significantly between finger tapping, line drawing, and circle drawing, suggesting separable sources of timing variability. The slopes of the 2 circle-drawing tasks did not differ from one another, nor did the slopes of the 2 line-drawing tasks differ significantly, suggesting a shared timing process within those tasks. Those results are evidence of a high degree of specificity in timing processes.     

Single-Joint Movements in Parkinson's Disease: A Pulse-Width and Pulse-Height Theory Review

The process by which the brain controls single-joint movements (SJM) is still not well understood. Some studies have defined rules describing the duration and magnitude of the agonist and antagonist muscles. Therefore, the purpose of this study was to analyze scientific publications about the electromyographic characteristics of SJM performed by patients with Parkinson's disease. A bibliographical review of the years 1989–2015 was performed using keywords such as electromyography, upper limb, and Parkinson's disease. After applying the inclusion criteria, 8 articles were included for analysis. The literature indicates that despite the lack of studies, it is possible to assume that considering the SJM, those with Parkinson's disease only control the magnitude of electromyography activation, being consistent only with the pulse-height theory control.     

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.     

Form and Variability During Sit-to-Stand Transitions: Children Versus Adults

In performing the sit-to-stand transition, young children (6- to 7-year-olds) were expected to display a movement form similar to that of adults. However, movement consistency was predicted to be poorer in children than in adults because they lack refinement of motor control processes. Kinematic analysis of 10 repetitions of the sit-to-stand movement was carried out for 6 typically developing children and 6 adults. Supporting the authors' prediction of comparable form, no differences were evident between age groups for sequence of joint onsets, proportional duration of segmental motion, or in angle-angle plots of displacement at 2 segments. In contrast, within-participant variability was found to be higher for children: Coefficients of variation for most kinematic measures were twice those seen for adults. The authors interpret the children's lack of movement consistency as a reflection of inadequate stabilization of an internal model of intersegmental dynamics. Whereas adults have attained a skill level associated with refinement of that model, children have not. Children have an additional control problem because changes in body morphology throughout childhood require ongoing updating of the internal model that controls intrinsic dynamics.