Adaptive Dynamics of the Leg Movement Patterns of Human Infants: III. Age-Related Differences in Limb Control

In this article, the development of the increasingly differentiated control of the joints necessary to transform the spontaneous leg movements of early infancy into adaptive and functional actions is described. The hypothesis-that increasing joint control requires the capability for disassociation of joint action, the active modulation of joint stiffness, and a transition from proximal to distal control of the joints-is proposed. Kinematic and kinetic analyses of the vertical kicks of infants 2 weeks, 3 months, and 7 months of age (as well as a comparative group of adults) indicated increasing joint independence as well as phase-dependent and joint-dependent control modifications. The kicks of the younger infants were dominated by a proximal control strategy and minimal adjustments of the limb energetics during the flexion and extension phases of the kick. By 7 months of age, much larger modulations of the kick phases were observed as well as increasing evidence of distal control. These results revealed kinematic and kinetic patterns of emerging limb control between 2 weeks and 7 months of age.     

A Fully Automated,Quantitative Test of Upper Limb Function

ABSTRACT. The Rehabilitation Joystick for Computerized Exercise (ReJoyce, Rehabtronics Inc., Edmonton, Alberta, Canada), is a workstation on which participants exercise dexterous movement tasks in the guise of computer games. The system incorporates the ReJoyce Arm and Hand Function Test (RAHFT). Here the authors evaluate the RAHFT against the Action Research Arm Test (ARAT) and the Fugl-Meyer Assessment (FMA). All 3 tests were performed in 36 separate sessions in 13 tetraplegic individuals. Concurrent and criterion validities of the RAHFT were supported by a high level of correlation with the ARAT (r² = .88). Regarding responsiveness, the effect size of the RAHFT at week 6 of 1 hr/day exercise training was 1.8. Regarding reliability, the mean test–retest difference in RAHFT baseline scores was 0.67% ± 3.6%, which was not statistically significant. The RAHFT showed less ceiling effect than either ARAT or FMA. These data help validate the RAHFT as a quantitative, automated alternative to the ARAT and FMA. The RAHFT is the first comprehensive test of arm and dexterous hand function that does not depend on human judgment. It offers a standardized, quantitative outcome evaluation, which can be performed not only in the clinic, but also in the participant's home, administered by a remote therapist over the Internet.     

Children's Use of Gaze and Limb Movement Cues to Infer Deception

A sample of 96 children from kindergarten, 2nd, 4th, and 6th grades judged the truthfulness of peers who varied in gaze and limb movement while providing verbal communications. Results indicated that children attributed greater lying to the peers who displayed indirect rather than direct gaze and active rather than nonactive limb movement. The use of these cues was more evident in 4th- and 6th-grade children than it was in kindergarten and 2nd-grade children. Pilot studies indicated that adults and children as young as 5-6 years of age associated indirect gaze and active limb movement with anxiety. The findings are discussed with respect to children's theory of mind, concepts of lying, understanding of display rules, and learning of physiological cues associated with deception.     

Limb Segment Recruitment as Function of Movement Direction,Amplitude, and Speed

Coordination of limb segments in graphic motor behavior has been studied primarily in cyclic tasks. In the present study, limb segment recruitment patterns were investigated in a discrete line-drawing task. Subjects (N = 11) performed pointing movements varying in direction, amplitude, and speed. The contributions of index finger, hand, and arm to the movement were analyzed by evaluating the angular displacements in 7 joint dimensions. The results showed that amplitude and direction affected limb segment involvement in the same way they have been reported to affect it in cyclic movements. Upward left- (up-left) directed movements were primarily achieved by fingers and arm, whereas upward right- (up-right) directed movements were accomplished with the hand and the arm. Large amplitudes elicited not only an increase of proximal but also a decrease of distal limb segment involvement, especially in the up-left direction. In the present discrete pointing task, effects of speed on limb segment involvement were different from speed effects that were observed earlier in cyclic tasks: Larger limb segments became more involved in fast than in slow discrete movements. With respect to the timing of limb segment recruitment, all joints tended to move simultaneously, but small deviations from synchronous joint movement onset and offset were present. The results are discussed in the context of recent theories of limb segment coordination.     

Servo Hypotheses for the Biological Control of Movement

An analysis is made of equilibrium-point models for motor control, describing these models in the context of servo control mechanisms. We considered issues of speed and stiffness scaling that are incompatible with current formulations of the equilibrium-point models. A modification of the equilibrium-point models is proposed in which the central nervous system controls velocity as well as positions during the course of fast 1imb movements. Numerical simulations are presented that verify that such a servo control mechanism could successfully produce fast limb movements, as observed in human subjects     

Force Control Characteristics for Generation and Relaxation in the Lower Limb

We investigated the characteristics for force generation and relaxation using graded isometric contractions of the knee extensors. Participants performed the following tasks as quickly and accurately as possible. For the force generation task, force was increased from 0% to 20%, 40% and 60% of the maximal voluntary force (MVF). For the force relaxation task, force was decreased from 60% to 40%, 20% and 0%. The following parameters of the recorded force were calculated: error, time, and rate of force development. The error was consistently greater for force relaxation than generation. Reaction and adjustment times were independent of the tasks. The control strategy was markedly different for force relaxation and generation, this tendency was particularly evident for the lower limb compared to the upper limb.     

Model Predictive Impedance Control: A Model for Joint Movement

Impedance control has been suggested as the strategy employed by the central nervous system to control human postures and movements. A realization of this strategy is presented that uses a model predictive control algorithm as a higher motor controller. External disturbances are explicitly included in the model. The combination of 3 key factors-joint impedance control, model predictive controller, and external disturbance input-forms the basis for the generality of this model. The model was applied to 3 different types of joint movements: a tracking movement with an unpredicted disturbance, a rhythmic movement, and an unstable biped model of human walking. Computer simulation results showed excellent performance of the model in all 3 cases for optimal values of active joint impedances and an exact match between the musculoskeletal system and the model internal to the model predictive controller. The controller was also able to maintain acceptable performance in the presence of a 25% mismatch between the musculoskeletal system and its internal model.     

Exploring the Limits of Peripheral Vision for the Control of Movement

The role played by peripheral visual information in the control of aiming movements is not fully understood, as is indicated by the conflicting results reported in the literature. In the present study, the authors tested and confirmed the hypothesis that the source of the conflict lies in the portion of the visual peripheral field that has been under scrutiny in the different studies. Participants (N = 60) moved a computer mouse from a fixed starting position to 1 of 3 targets under varied vision conditions. The portion of the peripheral visual field that best ensured directional accuracy of a sweeping movement was found to be located between 20° and 10° of visual angle, whereas the area found to favor directional accuracy of an aiming movement comprised 30° through 10° of visual angle.     

Modeling the Neurological Control of Human Movements

Although computer models have been extensively used in recent years to understand the way physical systems operate and interact, the enormous power of mathematical modeling and computer simulations has been difficult to implement for the benefit of neuroscientists studying the human motor control system. Nevertheless, homeomorphic models are now being used to explain and predict the neural and biomechanical aspects of different human movements. This paper argues for the importance of regarding model simulations as a supplementary approach to traditional methods of experimental investigation by drawing examples from both the experimental and the modeling literature. The discussion focuses on studies of the triphasic control signal for fast, goal-directed movements and on aspects of sampled data control for slow, tracking movements. The aim of this viewpoint article is to promote a more widespread use of modeling and simulation in the field of motor control.     

Movement Variability Increases With Shoulder Pain When Compensatory Strategies of the Upper Body Are Constrained

This cross-sectional study analyzed the influence of chronic shoulder pain (CSP) on movement variability/kinematics during humeral elevation, with the trunk and elbow motions constrained to avoid compensatory strategies. For this purpose, 37 volunteers with CSP as the injured group (IG) and 58 participants with asymptomatic shoulders as the control group (CG) participated in the study. Maximum humeral elevation (Emax), maximum angular velocity (Velmax), variability of the maximum angle (CVEmax), functional variability (Func_var), and approximate entropy (ApEn) were calculated from the kinematic data. Patients' pain was measured on the visual analogue scale (VAS). Compared with the CG, the IG presented lower Emax and Velmax and higher variability (i.e., CVEmax, Func_var, and ApEn). Moderate correlations were achieved for the VAS score and the kinematic variables Emax, Velmax and variability of curve analysis, Func_varm, and ApEn. No significant correlation was found for CVEmax. In conclusion, CSP results in a decrease of angle and velocity and an increased shoulder movement variability when the neuromuscular system cannot use compensatory strategies to avoid painful positions.     

A Note on the Speed-Amplitude Function in Movement Control

An experiment is reported that documents the maximum average speed-amplitude relationship across the full range of motion for elbow flexion. Minimum movement time increased as a negative exponential within the movement range up to 94-97% of the maximum range of motion. At this point a discontinuity occurred with movement time increasing at an increasing rate probably due to anatomical and morphological constraints. These results suggest that the maximum average velocity-amplitude boundary to the movement speed-accuracy relationship is curvilinear. Kinematic analysis of the movements as a function of range of motion suggests that a simple pulse-step model of movement control cannot account for the present findings.     

Monocular and Binocular Vision in the Control of Goal-Directed Movement

In the present research the authors examined the time course of binocular integration in goal-directed aiming and grasping. With liquid-crystal goggles, the authors manipulated vision independently to the right and left eyes of 10 students during movement preparation and movement execution. Contrary to earlier findings reported in catching experiments (I. Olivier, D. J. Weeks, K. L. Ricker, J. Lyons, & D. Elliott, 1998), neither a temporal nor a spatial binocular advantage was obtained in 1 grasping and 2 aiming studies. That result suggests that, at least in some circumstances, monocular vision is sufficient for the precise control of limb movements. In a final aiming experiment involving 3-dimen- sional spatial variability and no trial-to-trial visual feedback about performance, binocular vision was associated with greater spatial accuracy. Binocular superiority appeared to be most pronounced when participants were unable to adjust their limb control strategy or procedure on the basis of terminal feedback about performance.     

Eye Movement Control During Reading: Foveal Load and Parafoveal Processing

We tested theories of eye movement control in reading by looking at parafoveal processing. According to attention-processing theories, attention shifts towards word n+1 only when processing of the fixated word n is finished, so that attended parafoveal processing does not start until the programming of the saccade programming to word n+1 is initiated (Henderson & Ferreira, 1990; Morrison, 1984), or even later when the processing of word n takes too long (Henderson & Ferreira, 1990). Parafoveal preview benefit should be constant whatever the foveal processing load (Morrison, 1984), or should decrease when processing word n outlasts an eye movement programming deadline (Henderson & Ferreira, 1990). By manipulating the frequency and length of the foveal word n and the visibility of the parafoveal word n+1 , we replicated the finding that the parafoveal preview benefit is smaller with a low-frequency word in foveal vision. Detailed analyses, however, showed that the eye movement programming deadline hypothesis could not account for this finding which was due not to cases where the low-frequency words n had received a long fixation, but to cases of a short fixations less than 240 msec. In addition, there was a spill-over effect of word n to word n+1 , and there was an element of parallel processing of both words. The results are more in line with parallel processing limited by the extent to which the parafoveal word processing on fixation n can be combined with the foveal word processing on fixation n+1 .     

Emotion and Motor Control: Movement Attributes Following Affective Picture Processing

The authors investigated the impact of emotion on the performance of a square-tracing task after participants (N = 40) were exposed to pleasant (P), unpleasant (U), and neutral (N) pictures. Physiological and self-report measures indexed affective valence and arousal. In Experiment 1, greater error followed exposure to 4 consecutive U images than exposure to 4 consecutive P images. Speed of performance did not vary as a function of valence. In Experiment 2, participants viewed 1 slide per trial within a modified exposure protocol. Speed of performance varied as a function of valence; faster performance followed U relative to P stimuli. Accuracy of performance did not vary between conditions. Corresponding self-report and physiological measures generally corroborated previous evidence. Findings collectively indicated that the length of exposure to affective stimuli mediates speed and accuracy of motor performance; compared with P stimuli, U stimuli led to either increased error (short exposure) or increased speed (multiple exposures). The authors conclude that brief and extended exposures to affective pictures have direct behavioral consequences, and they discuss the implications of that finding.     

Movement Control in a Reciprocal Tapping Task

A cross-sectional approach was used to replicate and examine developmental flexibility in eye-hand relationships during alternate tapping performance. A group of 68 male subjects, 34 younger (mean 75.6 months) and 34 older (mean 128.9 months) practiced 12 5-sec trials of alternate tapping in one of three accuracy conditions. Trials 2 and 11 were filmed to determine the eye movement index (EMI), a fraction relating eye movements (numerator) to alternate taps (denominator). Fractional EMI values close to 1 were labelled discontinuity and values closer to 0 (1/N) continuity. Accuracy variation tested the flexibility of EMI. for developmental change, revealing that EMIs for older subjects were more continuous than for younger subjects at trial 11, but not at trial 2. Level of EMI was related to age and condition, while change in EMI due to practice was related to age. The data showed EMI strategy flexibility increased with age, and that faster tapping was afforded by less direct visual monitoring of the hand.     

Shoulder Muscle Activity Dampens Arm Swing Motion When Altering Upper Limb Mass Characteristics During Locomotion

Weighting the arms during locomotion results in decreased swing motion and increased shoulder muscle activity. To determine the functional relevance of this activity, participants walked on a treadmill with the arms unweighted, or weighted unilaterally or bilaterally. Similar to past work, the weighted arms decreased in swing amplitude and increased their shoulder muscle activity. A close examination of shoulder muscle activities in specific regions of the arm swing cycle suggested these muscles primarily acted eccentrically for all weighting conditions. These findings suggest that the increased shoulder muscle activities when weighting the arms act to dampen the arms when the inertial characteristics of the arms are altered, as opposed to assisting in driving swing of the heavier arms.     

酒精对视觉加工和眼动行为控制的影响(中文)

Although moderate alcohol consumption is known to degrade performance in a variety of tasks, the exact nature and extent of such impairments is not well understood. We examined alcohol effects on different levels of visual processing and oculomotor control. On the lowest level(automatic), reflexive responses were tested using the prosaccade task. The‘automated’level, incorporating routine behavior based on implicit learning, was studied using the double step paradigm, while the highest level, representing voluntary control, was examined with antisaccade and memory guided tasks. In addition, sentence reading was included as a prototypical complex task with high ecological validity. Participant′s baseline performance was compared to alcohol conditions with intoxication levels around 70mg% of breath alcohol concentration. Functioning on the automatic level was intact, except for a substantial slowing in saccade latencies. On the automated level, deficits in the ability to adaptively reprogram saccades on the basis of new information were found. Impairments in voluntary control were apparent in hypermetric saccade amplitudes whenever a reprogramming of the initial saccade target was necessary. There was also a small but significant detrimental effect on visuospatial short term memory. Somewhat surprisingly, no alcohol related deficits emerged with regard to inhibitory functions. ‘Reading under the influence’resulted in substantially prolonged fixation durations with only a modest increase in total viewing time per word. A trade-off between increased duration and decreased number of fixations pointed to the possibility that the extra time available under alcohol can be used for linguistic processing, which in itself did not appear to be impaired. This idea is supported by the fact that there was no interaction between alcohol and word frequency. Contrary to expectation, the processing of parafoveal information during reading was not impeded. Overall, results provide a largely coherent pattern of selective effects that begin to form a comprehensive picture of alcohol related deficits.     

Attention Is Required to Coordinate Reaching and Postural Stability during Upper Limb Movements Generated While Standing

Abstract

In the present study we investigated how attention contributes to the interaction between reach planning and execution, and postural control. Reaching movements were generated while standing and were performed either in isolation or in conjunction with a secondary reaction time (RT) task. In addition, to better understand how online movement control is affected by this interaction, the reaching movements could be unexpectedly perturbed medial-laterally. Postural kinetic, arm kinematic and RT, and secondary RT measures were used to characterize the responses. Results indicate task performance worsened when both the reaching and secondary tasks were completed simultaneously. Our results imply the generation of reaching movements while standing requires attentional resources to properly coordinate the interaction between the reaching task and postural control.