Speed-sensitive Strategy Research Articles

Latency Cost and Information: Does Speed Matter for All Market Participants?

The author examines latency cost—a trading cost dimension arising from the delay in time between an order submission decision and execution—across traders with different levels of information in U.S. equities. He finds that both traders who appear informed and uninformed about future prices experience a cost induced from latency. However, the uninformed pay a significantly higher cost. The results indicate that having access to faster trading speed is beneficial, even for traders using less speed-sensitive strategies.

The effect of target size and inertial load on the control of rapid aiming movements. A test of speed-sensitive and speed-insensitive strategies.

Two experiments are reported that investigated the effects of target size and inertial load on the control of rapid aiming movements. Based on kinematic profiles, movements were partitioned into their preprogrammed initial impulse- and feedback-based error correction phases. Electromyographic (EMG) rise rates were examined to investigate whether participants used a speed-sensitive or speed-insensitive control strategy. The results from both experiments showed that initial impulse velocity and EMG rise rates varied as a function of target size, i.e., a speed-sensitive strategy. This was the case whether participants were allowed to make error corrections to their movements (experiment 1) or were instructed to produce initial impulses that hit the target (experiment 2). Both experiments also showed that initial impulse velocity and endpoint variability were inversely related to inertial load. The results from experiment 2 indicated that, while the manipulation of inertial load had no effect on EMG rise rates for movements to a large target, EMG slopes were modulated between inertial load conditions when the target was small.

Principles for learning single-joint movements. I. Enhanced performance by practice.

This study investigated changes in myoelectric and mechanical variables for movements made "as fast as possible" as a function of practice in the context of the dual-strategy hypothesis of motor control (Gottlieb et al. 1989b). Five male subjects made 1400 rapid elbow flexion movements in ten blocks of 20 trials over seven experimental sessions. Improved performance was defined as increased peak movement velocity, decreased peak velocity variability, increased acceleration and deceleration, a proportionately greater increase in peak deceleration than peak acceleration, and greater consistency in terminal location. The changes observed over experimental sessions were very similar to (but larger and more consistent than) those seen for the first experimental session, with the partial exception of the timing of the antagonist electromyogram (EMG). In general, the increases in the values of the measured mechanical variables covary with myoelectric measures in the same way as when subjects are asked to intentionally change speed in accordance with the rules of the speed-sensitive strategy (Corcos et al. 1989). However, there are differences between subjects in the extent to which speed changes can be attributable to the agonist muscle, the antagonist muscle, or in the timing between the muscles. In one of the five subjects, the latency of the antagonist EMG decreased over blocks on the 1st day but increased over experimental sessions and was consequently activated proportionately later in the movement. This suggests that extended practice can give at least some subjects flexibility in modifying the motor programs that underlie movement.

Theories for Skilled Limb Movements .

Some of the theories that have been advanced to perform skilled limb movements are reviewed in this paper. The aspects discussed in brief include alpha-gamma control, choice of control variables in limb movements, equilibrium point hypotheses, experimental observations from simple movement studies and explanations proposed, in particular the dual strategy hypothesis. The single mechanical degree-of-freedom movements may be controlled by one of two strategies: a speed-insensitive strategy or a speed-sensitive strategy. The term strategy implies a set of rules which specify in terms of task variables and subject instructions how to choose the excitation signal, the controlling signal at the alpha motoneuron level. The two strategies differ in that speed-insensitive strategy is a result of duration modulation of the excitation pulse, whereas the speed-sensitive strategy is a result from amplitude modulation. Finally, the problem of multi-degrees of freedom movements and the role of higher motor control centres are discussed in brief.

Organizing principles for single joint movements: V. Agonist-antagonist interactions.

1. Normal human subjects made discrete elbow flexions in the horizontal plane under different task conditions of initial or final position, inertial loading, or instruction about speed. We measured joint angle, acceleration, and electromyographic signals (EMGs) from two agonist and two antagonist muscles. 2. For many of the experimental tasks, the latency of the antagonist EMG burst was strongly correlated with parameters of the first agonist EMG burst defined by a single equation, expressed in terms of the agonist's hypothetical excitation pulse. Latency is proportional to the ratio of pulse duration to pulse intensity, making it proportional to movement distance and inertial load and inversely proportional to planned movement speed. However, these rules are not sufficient to define the timing of every possible single joint movement. 3. For movements described by the speed-insensitive strategy, the quantity of both antagonist and agonist muscle activity can be uniformly associated with selected kinetic measures that incorporate muscle force-velocity relations. 4. For movements collectively described by the speed-sensitive strategy, (i.e., that have direct or indirect constraints on speed), no single rule can describe all the combinations of agonist-antagonist coordination that are used to perform these diverse tasks. 5. Estimates of joint viscosity were made by calculating the amount of velocity-dependent torque used to terminate movements on target. These estimates are similar to those that have previously been made of limb viscosity during postural maintenance. They imply that a significant component of muscle activity must be used to overcome these forces. 6. These and previous results are all consistent with a dual-strategy hypothesis for those single-joint movements that are sufficiently fast to require pulse-like muscle activation patterns. The major features of such patterns (pulse intensities, durations, and latencies) are determined by central commands programmed in advance of movement initiation. The selection between speed-insensitive or speed-sensitive rules of motoneuron pool excitation is implicitly specified by the nature of speed constraints of the movement task.

Virtual trajectories of single-joint movements performed under two basic strategies

The framework of the equilibrium point hypothesis has been used to analyse motor control processes for single-joint movements. Virtual trajectories and joint stiffness were reconstructed for different movement speeds and distances when subjects were instructed either to move “as fast as possible” or to intentionally vary movement speed. These instructions are assumed to be associated with similar or different rates of change of hypothetical central control variables (corresponding to the speed-sensitive and speed-insensitive strategies). The subjects were trained to perform relatively slow, moderately fast and very fast (nominal movement times 800, 400 and 250 ms) single-joint elbow flexion movements against a constant extending torque bias. They were instructed to reproduce the motor command for a series of movements white ignoring possible changes in the external torque which could slowly and unpredictably increase, decrease, or remain constant. The total muscle torque was calculated as a sum of external and inertial components. Fast movements over different distances were made with the speed-insensitive strategy. They were characterized by an increase in joint stiffness near the midpoint of the movements which was relatively independent of movement amplitude. Their virtual trajectories had a non-monotonic N-shape. All three arms of the N-shape scaled with movement amplitude. Movements over one distance at different speeds were made with a speed-sensitive strategy. They demonstrated different patterns of virtual trajectories and joint stiffness that depended on movement speed. The N-shape became less apparent for moderately fast movements and virtually disappeared for the slow movements. Slow movements showed no visible increase in joint stiffness. The joint stiffness patterns have been shown to depend upon central control processes rather than on actual values of joint velocity. We conclude that the two basic central strategies have characteristic patterns by which the equilibrium trajectory and joint stiffness are modulated.

EMG area scaling and velocity modulations in a spatiotemporally constrained movement

Research examining the electromyographic (EMG) burst structure of rapid discrete limb movements has led to discordant findings concerning agonist burst duration. Some research has shown that duration varies as a function of movement speed while other research has shown burst constancy. Unfortunately, much of this research may be confounded by not carefully controlling movement termination accuracy and movement time (MT). Due to these potential problems, the present study was conducted to determine the effects of strict spatiotemporal constraints on EMG characteristics of a rapid elbow flexion-extension response under two movement extent conditions across five different MTs. Results revealed that a decreased MT was accompanied by a decreased agonist (biceps) burst duration and increased agonist burst amplitude. The burst duration and amplitude both increased as the movement extent increased with MT held constant. None of three current theoretical perspectives of rapid movement control (the impulse-timing model, the speed-control system hypothesis, or the speed-sensitive strategy) could fully account for these results. Instead, a control strategy was exhibited in which moving faster was accomplished by relative scaling of burst area via concomitant expansion of burst amplitude and compression of burst duration.

Organizing principles for single-joint movements. IV. Implications for isometric contractions

1. Normal human subjects made isometric pulse and step contractions about the elbow to visually defined target torques of different amplitudes and at different rates. We measured joint torque and electromyograms (EMG) from two agonist and two antagonist muscles. 2. When the task specification requires that the subject explicitly alter the rate at which torque is increased, the rates of rise of the agonist and antagonist EMG bursts covary with the rate of rise of the torque. For pulses of torque the duration of motoneuron excitation varies with the duration of the task-defined contractile event. 3. When a subject is asked to generate torques of different amplitudes without specifying a time interval, torque amplitude is positively correlated with how long, and therefore how high, the EMG rose. Subjects usually proportionately covary the strength of the agonist and antagonist contractions but are not constrained to do so. Some subjects use a strategy of varying the antagonist inversely with the agonist contraction. 4. We extend the organizing principles for the control of movement about a single joint to the control of isometric torque. These rules state that control of torque about a single joint is exercised by one of two strategies: the speed-sensitive strategy modulates the rate at which contraction rises by varying the intensity of motoneuron-pool excitation. The speed-insensitive strategy varies the duration over which contraction rises but does not change the rate. These two respective patterns of torque emerge from pulse-height and pulse-width modulation of motoneuron-pool excitation. 5. The rules defining speed-sensitive and speed-insensitive strategies for movements are broadened for isometric contractions because of the wider range of torque patterns that we observe under these conditions. We propose a step-excitation component for prolonged isometric step contractions and slowly rising ramp patterns of excitation for contractions that develop over several hundreds of milliseconds. 6. The choice of strategies is based on task-specific torque requirements. The same two strategies that control torque to produce movement apply to the control of isometric torque. Unlike movements, however, isometric tasks are more often controlled by a blending of the two patterns. Possible reasons for this are discussed.

Organizing principles for single-joint movements. II. A speed-sensitive strategy.

1. Normal human subjects made discrete flexions of the elbow over a fixed distance in the horizontal plane from a stationary initial position to a visually defined target. We measured joint angle, acceleration, and electromyograms (EMGs) from two agonist and two antagonist muscles. 2. Changes in movement speed were elicited either by explicit instruction to the subject or by adjusting the target width. Instructions always required accurately stopping in the target zone. 3. Peak inertial torques and accelerations, movement times, and integrated EMGs were all highly correlated with speed. We show that inertial torque can be used as a linking variable that is almost sufficient to explain all correlations between the task, the EMG, and movement kinematics. 4. When subjects perform tasks that require control of movement speed, they adjust the rate at which torque is developed by the muscles. This rate is modulated by the way in which the muscles are activated. The rate at which joint torque develops is correlated with the rate at which the agonist EMG rises as well as with integrated EMG. 5. The antagonist EMG shows two components. The latency of the first is 30-50 ms and independent of movement dynamics. The latency of the second component is proportional to movement time. The rate of rise and area of both components scale with torque. 6. We propose organizing principles for the control of single-joint movements in which tasks are performed by one of two strategies. These are called speed-insensitive and speed-sensitive strategies. 7. A model is proposed in which movements made under a speed-sensitive strategy are executed by controlling the intensity of an excitation pulse delivered to the motoneuron pool. The effect is to regulate the rate at which joint torque, and consequently acceleration, increases. 8. Movements of variable distance, speed, accuracy, and load are shown to be controlled by one of two consistent sets of rules for muscle activation. These rules apply to the control of both the agonist and antagonist muscles. Rules of activation lead to distinguishable patterns of EMG and torque development. All observable changes in movement kinematics are explained as deterministic consequences of these effects.

Organizing principles for single-joint movements. I. A speed-insensitive strategy.

1. Normal human subjects made discrete elbow flexions and extensions in the horizontal plane from a stationary initial position to visually defined targets at different distances with a constant inertial load or made flexions to a visually defined target with different inertial loads. We measured joint angle, acceleration, and electromyograms (EMGs) from two agonist and two antagonist muscles. 2. Subjects were instructed to move their limbs accurately but quickly to the targets. Movements of greater distances or lesser loads were performed at higher velocities. 3. Peak inertial torque, acceleration and velocity, movement time, and integrated, rectified EMG were all highly correlated with the task variables, distance and inertial load. We show that peak inertial torque can be used as a linking variable that is almost sufficient to explain all correlations between the tasks, the EMG, and movement kinematics. 4. The rate at which subjects initially developed torque to accelerate their movements was invariant over changes in the value of either task variable. The rising phase of the agonist EMG was also independent of the distance or load moved. 5. Two components were distinguished in the antagonist EMG. The first had a relatively constant latency and amplitude. It terminated on the onset of the second and larger component at a latency that was delayed as both distance and load increased. 6. The integrated, rectified antagonist EMG was proportional to inertial load and peak decelerating torque for changes in inertial load. When target distance varied, proportionality between peak decelerating torque and antagonist EMG could be found if correction was made for the effects of muscle length on the torque-EMG relationship. 7. We propose organizing principles for the control of single-joint human movements in which tasks are performed by one of two strategies. These are called speed-insensitive and speed-sensitive strategies. 8. A model is described in which movements made under a speed-insensitive strategy are executed by controlling the duration and the relative timing of amplitude invariant patterns of activation to the spinal motoneuron pools.

Speed-insensitive and speed-sensitive strategies in multijoint movements

Speed-insensitive and speed-sensitive strategies in multijoint movements

Strategies for the control of voluntary movements with one mechanical degree of freedom

AbstractA theory is presented to explain how accurate, single-joint movements are controlled. The theory applies to movements across different distances, with different inertial loads, toward targets of different widths over a wide range of experimentally manipulated velocities. The theory is based on three propositions. (1) Movements are planned according to “strategies” of which there are at least two: a speed-insensitive (SI) and a speed-sensitive (SS) one. (2) These strategies can be equated with sets of rules for performing diverse movement tasks. The choice between SI and SS depends on whether movement speed and/or movement time (and hence appropriate muscle forces) must be constrained to meet task requirements. (3) The electromyogram can be interpreted as a low-pass filtered version of the controlling signal to the motoneuron pools. This controlling signal can be modelled as a rectangular excitation pulse in which modulation occurs in either pulse amplitude or pulse width. Movements to different distances and with loads are controlled by the SI strategy, which modulates pulse width. Movements in which speed must be explicitly regulated are controlled by the SS strategy, which modulates pulse amplitude. The distinction between the two movement strategies reconciles many apparent conflicts in the motor control literature.