Showing papers in "Journal of Motor Behavior in 1986"

Once More on the Equilibrium-Point Hypothesis (λ Model) for Motor Control

Abstract: The equilibrium control hypothesis (λ model) is considered with special reference to the following concepts: (a) the length-force invariant characteristic (IC) of the muscle together with central and reflex systems subserving its activity; (b) the tonic stretch reflex threshold (λ) as an independent measure of central commands descending to alpha and gamma motoneurons; (c) the equilibrium point, defined in terms of λ, IC and static load characteristics, which is associated with the notion that posture and movement are controlled by a single mechanism; and (d) the muscle activation area (a reformulation of the “size principle”)— the area of kinematic and command variables in which a rank-ordered recruitment of motor units takes place. The model is used for the interpretation of various motor phenomena, particularly electromyographic patterns. The stretch reflex in the λ model has no mechanism to follow-up a certain muscle length prescribed by central commands. Rather, its task is to bring the system to an ...

Grasp size and accuracy of approach in reaching.

Abstract: In reaching for an object in the environment, it has been suggested that movement components concerned with transport of the hand toward the object and those related to grasping the object are organized and executed independently. An experiment is reported that demonstrates people adjust grasp aperture to compensate for factors affecting transport error. Grasp aperture was found to be greater in reaching movements performed faster than normal, and grasp aperture was also found to be wider when reaching with the eyes closed. In both cases, transport was spatially less accurate. It is argued that, in advance of movement, formation of grasp is planned to take into account not only the perceived characteristics of the object but, also, internalized information based on past experience about the likely accuracy of the transport component.

Kinematic Properties of Rapid Aimed Hand Movements

Abstract: Generalized motor program theory and the models of Schmidt, Zelaznik, and Frank (1978), and Meyer, Smith, and Wright (1982) of speed-accuracy relationships in aimed hand movements require that the underlying acceleration-time patterns exhibit time rescalability, in which all acceleration-time functions in an aimed hand movement are generated from one rescalable pattern. We examined this property as a function of movement time in Experiment 1, and as a function of movement time and movement distance in Experiment 2. Both experiments failed to demonstrate strict time rescalability in acceleration-time patterns, with the time to peak positive acceleration being invariant across movement time. This suggests that time rescalability is not a necessary condition for the linear relation between speed and spatial variability. A second major finding was that the variability in distance traveled at the end of positive acceleration was independent of movement time, contrary to the symmetric-impulse-variability model of Meyer et al. (1982). The findings of both experiments suggest that the processes involved in decelerating the limb play an important, but yet to be understood, role in determining the linear speed-accuracy trade-off. Finally, these results suggest that generalized motor programs are not based on simple, time-rescalable acceleration patterns.

Joint control strategies and hand trajectories in multijoint pointing movements.

Abstract: The role of timing in the control of multijoint pointing movements was evaluated. Eight subjects performed rapid pointing movements to a variety of target locations. The subject’s right arm was strapped to a 2° of freedom manupilandum that permitted shoulder and elbow motion in the horizontal plane. Initial and final position of the hand and magnitude of displacement was varied to determine effects on timing characteristics. Kinematics and kinetics of the shoulder, elbow, and hand were analyzed.The hand paths and velocity profiles observed were consistent with prior reports. Multiple regression analysis of kinematic variables disclosed that timing of joint movement onset was independent of initial and final positions of the hand, but was linearly related to joint displacement: the joint that moved farther started moving first. Using computer simulations to create joint movement onset, times that were different from the observed ones always resulted in hand paths with increased curvatures and loss of the s...

Kinematic and electromyographic changes that occur as a function of learning a time-constrained aiming task.

Abstract: The present study attempted to examine the changes associated with learning two time-constrained aiming movements at the neuromuscular and behavioral levels of analysis. Electromyographic data and movement kinematics were used to assess changes due to practice. Eight right-handed females were required to perform a 45° horizontal forearm extension in either 200 ms or 500 ms for 100 trials on each of four consecutive days. Both groups demonstrated an improvement in performance and a decrease in within-subject variability in the endpoint response measures, movement trajectory, and myoelectric pattern. With practice, there was a decrease in the amount of cocontraction between the agonist and antagonist muscles during movement execution, which indicated an elimination of unwanted neural activity. For the 200 ms task, the acceleration profile became symmetrical and a triphasic myoelectric pattern became evident. The deceleratory phase of the 500 ms task was longer than the acceleratory phase, and a biphasic pat...

An examination of rapid positioning movements with spatiotemporal constraints.

Abstract: Unidirectional positioning movements with spatiotemporal-constraints were examined as a test of impulse-timing theory (Schmidt, 1976; 1980; Wallace, 1981). Movements were examined at the kinematic, kinetic, and neuromuscular levels in three experiments. In the first experiment, displacement was held constant while five different movement times were examined. Both amplitudes and durations of the EMG and the kinetic variables were related to movement time. The results generally support the impulse-timing model. In the second experiment, movements were performed to a target at each of four distances in a constant movement time. EMG and force amplitudes and, unexpectedly, accelerative-force duration were modulated to achieve changes in displacement when movement time was constant. In the third experiment, movement time and displacement were simultaneously varied resulting in four conditions with equal average velocities. The results of this experiment were not as clear and exhibited individual differences. EM...

Planning and timing of finger-tapping sequences with a stressed element.

Abstract: Advance planning and execution-time organization of sequences of five finger taps were studied in four experiments. Intertap intervals were required to be equal. In some experimental conditions, one of the taps had to be stronger than the other four. Serial position of the stressed tap, number of alternative stress positions, and tapping rate were manipulated. Time to initiate the sequence after presentation of a reaction stimulus (RT), intertap intervals, and force of the taps were measured. the different effects of stress production and choosing between alternative stress locations on the RT of fast as compared to slow sequences suggest that a plan was selected and activated for the whole sequence only when it had to be executed at a fast rate. Additional organization of the fast sequences during execution was inferred from the intertap intervals, force patterns, and stress location errors, that were all different from those observed in slow sequences. The effects of stress production on timing are discussed in relation to existing timing models.

Controlling velocity in rapid movements.

Abstract: It has often been reported that subjects prefer to use a strategy in which they vary movement velocity and peak amplitude in a linear fashion. In this study, control of velocity and amplitude in rapid reciprocating movements of the interphalangeal joint of the thumb was investigated by examining movement trajectories and patterns of activity in the extensor pollicis longus (EPL) and flexor pollicis longus (FPL) muscles. In controlling either amplitude or peak flexion velocity without constraint, subjects always used a strategy in which peak extension velocity and peak flexion velocity had strong linear correlations with movement amplitude. When they were required to keep either amplitude or peak flexion velocity fixed their movements were still biased toward a strategy in which peak velocity and movement amplitude covaried. It is suggested that the preferred strategy is related to a basic principle of scaling the magnitude and duration of a velocity profile in order to achieve different movement amplitudes.

Force and timing components of the motor program.

Abstract: Three experiments were undertaken to assess the effects of variations of force and time on both simple and choice reaction time. The first two experiments demonstrated that although latency did not vary as a function of force, timing variations, such as requiring that a response be maintained, led to consistent changes in reaction time. These results led to the development of a model of motor programming in which force and timing are dissociated as separate components. However, the data also indicated that the force component may be further analyzed into two subcomponents—force activation and force deactivation. The model predicts that the latter subcomponent may be programmed on-line provided that sufficient time elapses between the implementation of the two subcomponents. A different pair of movements was used in Experiment 3 to further demonstrate that force activation and deactivation may be preprogrammed into a single component. These results support the aspect of the proposed model that makes a dist...

Chronometric analysis of the posturo-kinetic programming of voluntary movement.

Abstract: Posturo-kinetic programming was investigated in a simple reaction time paradigm. Standing subjects performed voluntary upper limb elevations under three conditions differing by the importance of their destabilizing effect on the initial balance. Three indexes were considered: the reaction time (RT) corresponding to delay between the response signal (RS) and the onset of the upper limb acceleration at wrist level (Aw); the motor latency (ML) corresponding to delay between RS and onset of the earlier of the two accelerations at shank level (As) which was previously shown to indicate the onset of postural adjustments; and the postural anticipation (PA) corresponding to the delay between the onset of the earliest As and the onset of Aw. The results showed that the RT varied in relation to parameters of the forthcoming movement. RT variations were essentially due to differences in the PA. It appeared that the ML depended on cognitive factors while the PA depended on biomechanical ones. It is concluded that ML ...

Oscillator mechanisms in the human motor system: investigating their properties using the aftercontraction effect.

Abstract: It is proposed that the human motor system is organized to use hardware and/or software non-linear oscillator mechanisms, the output of these oscillators being responsible for driving the limbs via signals to muscle groups. Following earlier theoretical development, it is argued that these muscle groupings act as a unit and themselves are likely to behave as a non-linear system. The attributes of non-linear oscillators are many, and they are potentially significant for the explanation of motor behavior. This paper reviews and presents recent experiments that investigated the properties of muscular aftercontraction. The basic finding shows that subsequent to a period of moderate strain against a fixed surface the treated limb exhibits prolonged involuntary molar oscillations in the plane of the treatment. These results provide for the presence of driving oscillator mechanisms in the human motor apparatus. The mechanisms show generality of action in that directed attention can lead to oscillation of untreated limbs. Overall, the experiments showed that the movements exhibited the mutual interaction, synchronization, and preservation of phase relationships that are fundamental properties of non-linear oscillators. the picture that emerges is that these mechanisms can drive involuntary movements that are richly patterned: like slow versions of voluntary movements. The aftercontraction phenomenon proves to be an excellent tool for research on the oscillatory substrate of human motor organization.

Motion variability--its definition, quantification, and origin.

Abstract: The concept of motion variability is discussed and a normalized measure for its quantification introduced. An example demonstrates that this new measure constitutes a global indicator of the current state of a motor learning process. The causes of motion variations are briefly discussed. They include initial perturbations of the skeletal, muscular, and neural systems as well as perturbations due to incremental changes, during motion execution, of external forces, muscular parameters (fatigue), afferent sensory inputs, and of the motor programs controlling the execution of the motion.

Interaction between visually and kinesthetically triggered voluntary responses.

Abstract: A voluntary motor response that is prepared in advance of a stimulus may be triggered by any sensory input. This study investigated the combination of visual and kinesthetic inputs in triggering voluntary torque responses. When a visual stimulus was presented alone, subjects produced a fast and accurate increase in elbow flexion torque. When a kinesthetic stimulus was presented instead of the visual stimulus, subjects produced a similar response with a reduced response latency. When a visual stimulus was presented in combination with a kinesthetic stimulus, subjects initiated their responses after either a visual or a kinesthetic response latency, depending on the relative timing of the two stimuli. An analysis of response amplitude suggested that when visual and kinesthetic stimuli were combined, both stimuli triggered a response. The results are more consistent with a simple behavioral model of addition of visual and kinesthetic responses (which predicts that the response to combined stimuli should be t...

Absolute error revisited: an accuracy indicator in disguise.

Abstract: When target accuracy is defined as the probability that an individual will respond to an accuracy task within a fixed distance around the target, then the composite error measures, E and AE, are shown to be fairly strong indicators of target accuracy in a relative sense. When AE and E are compared, AE is shown to be an even stronger accuracy indicator than E for most reasonable accuracy requirements. This, plus the fact that AE has certain desirable properties in ANOVA procedures, suggests that AE is a good, composite measure of target accuracy and should be analyzed first to determine if target accuracy differences exist. Subsequent analyses of bias and/or variability are then recommended.

Information processes in movement learning: capacity and structural interference effects.

Abstract: A series of experiments examined motor learning as an information processing activity occurring within a working short-term memory system and where response-produced feedback and knowledge of results (KR) are used to modify the action plan developed from previous attempts at the movement task. Use of interpolated activities in the KR delay interval allowed inferences to be made regarding the capacity and structural characteristics of these information processes. Results indicated no capacity limitations on the learning process but important structural effects were found. The results supported the idea that response-produced feedback is relatively unimportant as a feedback variable early in learning. Rather, the use of KR at a relatively high level of movement planning appears to be the important information processing activity underlying learning. Finally, the results supported the view that these information processes are related to cognitive problem solving activities.

Isn't there a catch in it somewhere?

Abstract: The relationship between skill level, vision, and proprioception in simple one-handed catching has recently been researched by Fischman and Schneider (1985). The parts of their work addressed to the necessity of being able to see the hand for optimal performance are critically evaluated in the light of earlier published studies, and other methodological and interpretative problems are signalled.

Impulse characteristics in rapid movement: implications for impulse-variability models.

Abstract: Three untested assumptions of the impulse-variability model were examined in two experiments utilizing rapid, uni-planar limb movements. Experiment 1 varied movement distance (A) and movement time (MT) in a rapid-timing paradigm where the subject moved a lever through a certain distance in a certain time. Experiment 2 varied A in a reversal response where the S made a rapid elbow flexion and extension in a given MT. Displacement recordings were made on every trial. KR (knowledge of results) about MT was given after every trial. The results can be summarized as follows: (a) As predicted by the model, variations in impulse size and velocity were directly related to the impulses size; (b) There was no correlation between the accelerative and decelerative impulse durations recorded during the reversal response supporting the notion that the impulses might be independent; (c) Negative correlations (–.20 to –.50) were demonstrated between peak acceleration and impulse duration for both experiments, counter to t...

A note: Is it a catch or a fumble?

Abstract: Following Whiting' (1986) comments on Fischman and Schneider (1985) and Smyth and Marriott (1982), this note addresses the questions of expertise in catching, the effects of sight of the hand on timing and positioning, and the difficulties of comparing performance in different experiments on catching.

Note on the effects of practice on reaction times.

Abstract: (1986). Note on the Effects of Practice on Reaction Times. Journal of Motor Behavior: Vol. 18, No. 3, pp. 343-345.

Development of the motor memory trace and control program.

Abstract: A theoretical explanation of the development of the memory trace constrained to fit into a computer analog requires a coded reference "image" of the intended motor act, a tentative control program (memory trace) based on mobilizing and coordinating various pre-established motor-control subroutines, and an afferent neural description of the act as actually performed. The afferent information is non-consciously compared with the reference image, and the resulting discrepancy used to modify the control program so as to reproduce the reference image more exactly on the next attempt. The discrepancy consists of the sum of two types of differences, between image and program (present during learning) and the error difference between program and performance. The trial-by-trial discrepancies cumulate in the memory trace, so that during both learning and postlearning practice the error component results in a within-individual odd-even trial correlation. This constitutes a mechanism for a remoteness effect in the inter-trial correlation matrix generated in a group of individuals during post-learning as well as learning conditions. Fifty-one individuals performed 50 trials on a simple arm movement task; 35 of these (the learners) showed individual systematic improvement during the first 20 trials but no improvement during the last 24; 16 (the non-learners) failed to improve with practice. Separate correlational analyses (both within- and inter-individual) of the two groups resulted in a variety of patterns that were predicted a priori in the learners by the theory, as did the 49 learners of another sample of 51 who performed a more complicated arm movement task. Also, as predicted, the non-learners failed to produce organized correlation patterns.

Adaptation level as an explanation of the peak shift in generalization with movement stimuli.

Abstract: Two experiments examine the value of adaptation level theory as an explanation of the peak shift phenomenon in stimulus generalization using linear arm movements. The first experiment manipulates the differences in adaptation levels during training by varying the frequency of experience of the training stimulus. Significant shifts in the peaks of generalization gradients were subsequently identified. The peak shifts were in the direction predicted by adaptation level theory. The second experiment manipulates testing adaptation levels by biasing the generalization test movements. Three groups of subjects performed differentially weighted test sequences in which the relative number of short, medium, or long movements was manipulated. Significant peak shifts of generalization gradients were observed in the direction predicted by adaptation level theory.

A note on issues in recent work on one-hand catching.

Abstract: Whiting’s (1986) comments on the necessity of viewing the hand in one-hand catching are acknowledged, and several empirical issues are raised for consideration. These issues revolve around (a) the two components of one-hand catching, (b) lack of independence of position and grasp errors, and (c) specificity of skill.

Temporal Disruptions in the “Accurate” Speech of Articulatory Defective Speakers and Stutterers

Abstract: Durational measures of vocalic steady states and transitions were made on phonetically accurate and fluently produced vowel-plosive, consonant-vowel bisyllables embedded in a carrier phrase. In the first experiment, these measures were taken from the speech of ten articulatory defective adult speakers and ten matched normal speakers. The second experiment analyzed durational measures in the speech of ten adult stutterers and ten matched nonstutterers. Using wideband spectrography, durational measurements were used to infer timing of articulatory movements during the subsegments of the VCV sequences. The results of both experiments suggest that the two groups of speech disordered subjects were able to produce transitional shifts appropriate to the phonetic environment but appeared to delay the initiation of coarticulatory movements. Aberrant speech timing may imply an involvement in the planning or integration of articulatory/coarticulatory movements rather than difficulty with movement execution per se.

The effect of age on relative timing variability and transfer.

Abstract: The purpose of this study was to investigate potential qualitative differences in relative timing across age both within and across speed conditions. Forty right-handed males performed 48 trials of a five-component coincident-timing task at one speed and then 16 more at a different speed. The independent variables were age (5-7, 8-10, 11-13 years, and adult), speed (slow and fast), and block order (training and transfer). The results indicated that within-speed relative timing consistency improved with increasing age for movement-time and pause-time components, while a cross-speed transfer improved with age only for pause time. Movement velocity emerged as a more stable timing parameter than movement time across speeds for all groups. The last movement-time component correlated highly with the total response times, suggesting that coincident-timing accuracy was controlled to a large degree by a final, fine-tuning correction. These results imply that developmental deficits in relative timing increase the a...

A note on modulations and structuring of locomotion in children and adults.

Abstract: The aim of this study was to investigate the modulations of locomotion induced by a rhythmic cognitive task (counting one's steps). Subjects (6- and 8-year-olds and adults) were requested to walk freely, and then to walk while counting their steps. Here a decrease in cadence values was observed in children only, with quasi-total repercussions on velocity at the age of 6 only. The spatiotemporal structuring of locomotion described here is already present at 6 years of age and is not altered in the step-counting situation: strong links were observed between cadence and velocity, and between stride length and velocity, and weak links between cadence and stride length.

Amending limb movements to mechanical perturbations under choice reaction time conditions.

Abstract: This paper examines the amendment of limb movements to mechanical perturbations under choice reaction time conditions. The two experiments reported were designed to examine the question of whether amendment latencies increase under choice conditions using two different choice manipulations. In Experiment 1, choice was manipulated by varying the duration of a mechanical perturbation in a known direction, while in Experiment 2 the strategy was to present perturbations of similar duration but unknown direction. Subjects produced discrete timing responses (700 ms-70 degrees) during which perturbations were interjected on random trials. The results reported reflect the outcome accuracy, the kinematics of the responses and latency of response modifications as a function of the various choice manipulations. The data demonstrated no statistically significant increases in reaction time as a function of choice manipulations. Although latencies did not significantly vary, both experiments demonstrated a significant decrease in response accuracy for the choice conditions. Collectively, the results are discussed in relation to the discrepancies between previous proprioceptive choice reaction time studies, which appear to stem from inconsistencies in both experimental methods and data analysis procedures.