Information processing and movement optimization during development: kinematics of cyclical pointing in 5- to 11-year-old children

The authors studied the development of movement control in speed-accuracy tradeoff conditions in children aged 5-11 years and in adults performing cyclical pointings. Twelve difficulty levels (IDs), ranging from 2 to 6.58 bits, were defined (P. M. Fitts, 1954). Peak and time to peak velocity, acceleration, and deceleration, and acceleration profiles as a function of hand position (Hooke's portraits) were analyzed. Movement time decreased with age and was less affected by ID. Peak velocity and acceleration increased, acceleration and deceleration were decreasingly time consuming, and movement profiles turned to increased harmonicity with age and task easiness. Nevertheless, the developmental trends differed between parameters. Gain in velocity seemed chiefly dependent on improved muscular cooperation patterns before 7 years of age and on improved information processing from age 7 onward; achievement of an optimized strategy in the speed-accuracy tradeoff occurred at age 11 years.     

Timing and accuracy of visually directed movements in children: control of direction and amplitude components

The reaction times (RTs), movement times (MTs), and final accuracy of hand movements directed towards visual goals were measured in 6-, 8-, and 10-year-old children, using tasks in which direction and amplitude components of movement were distinctly required. The tasks were performed with and without visual feedback of the limb. RTs decreased with age, and were shorter in directional than in amplitude task, in all ages. MTs were the longest at age 8 in both tasks, equally short at ages 6 and 10 in the directional task, the shortest at age 10, and intermediate at age 6, when amplitude had to be regulated. In the amplitude task, the target distance generally affected MTs under both visual conditions, but to a lower degree at age 10 than in the two younger groups. Movement accuracy, which was in all cases higher with visual feedback, showed different developmental trends among the two spatial components: directional accuracy was not different among the three groups of age, whereas amplitude accuracy showed a nonmonotonic development in the nonvisual condition, with an increase between age 6 and age 10, and the lowest level at age 8. In the visual condition, amplitude accuracy did not change with age. The specification of direction seems therefore to predominantly load the preparatory stage of the response. Amplitude specification seems to be more dependent on on-going regulations and to undergo a longer and more complex development, with a critical period around age 8 when a greater propensity for a feedback-based control appears on the two components. With increasing age, amplitude tends to be specific to a greater extent by a feedforward process.     

The attentional cost of amplitude and directional requirements when pointing to targets

The aim of this study was to investigate the comparative cost of accuracy constraints in direction or amplitude for movement regulation. The attentional cost is operationally defined as the amount of disturbance created in a secondary task by the simultaneous execution of a pointing task in direction or amplitude. The cost is expressed in terms of modifications in response to a secondary task, consisting of a foot-pedal release in response to an auditory stimulus (probe). The probe was introduced during the programming portion or the first, middle, or last portion of the pointing movement. The independent variables were the requirements of the task: direction or amplitude, and the moments of occurrence of the probe. Subjects were submitted to eight experimental conditions: (1) simple foot reaction time to a buzzer; (2) single directional task; (3) single amplitude task; (4) dual directional task (i.e. directional task with probe); (5) dual amplitude task (i.e. amplitude task with probe); (6) retest of foot simple reaction time; (7) retest of single directional task; and (8) retest of single amplitude task. Regulation in direction was more attention-demanding than regulation in distance in terms of programming. During pointing in amplitude, probe RT increased monotonically from start to end of movement execution, whereas directional pointing did not lead to any significant probe RT changes. These results emphasize the specific attentional loads for directional and amplitude pointing tasks, hence the involvement of different central nervous system mechanisms for the programming and regulation of the directional and amplitude parameters of pointing movements.     

Integrating fundamental movement skills in late childhood

The study examined how children of different ages integrate fundamental movement skills, such as running and throwing, and whether their developmental status was related to the combination of these skills. Thirty children were divided into three groups (G1 = 6-year-olds, G2 = 9-year-olds, and G3 = 12-year-olds) and filmed performing three tasks: running, overarm throwing, and the combined task. Patterns were identified and described, and the efficiency of integration was calculated (distance differences of the ball thrown in two tasks, overarm throwing and combined task). Differences in integration were related to age: the 6-year-olds were less efficient in combining the two skills than the 9- and 12-year-olds. These differences may be indicative of a phase of integrating fundamental movement skills in the developmental sequence. This developmental status, particularly throwing, seems to be related to the competence to integrate skills, which suggests that fundamental movement skills may be developmental modules.     

Development: Compared to what?: Contrast effects in age-comparative paradigms

Recent controversies about judgment competence of preschool and adolescent children are considered as being a possible product of contrast effects. That is, perceived abilities of children of a given age group may depend on the ages of the other subjects in the experiment. An experiment was done to test the possibility of contrast effects in age-comparative experiments. One group of subjects read about three experimental tasks in which 6-year-old children performed better than 4-year-olds. A second group read about 6-year-olds performing worse than 8-year-olds on the same tasks. Performance levels of 6-year-olds were the same on the two forms. For each task subjects rated the competence of each of the two age groups on the task and predicted the performance of the two groups on a related task. Undergraduate subjects' competence ratings and predictions were higher for 6-year-olds when compared to 4-year-olds than when compared to 8-year-olds. Psychology graduate students showed the same contrast effect for predictions but not for competence ratings. The results are discussed in terms of potential biases in age-comparative methods in developmental psychology.     

Response timing variability: coherence of kinematic and EMG parameters

A detailed kinematic and electromyographic (EMG) analysis of single degree of freedom timing responses is reported to (a) determine the coherence of kinematic and EMG variability to the reduced timing error variability exhibited with amplitude increments within a given criterion movement time and (b) understand the temporal organization of various movement parameters in simple responses. The data reveal that the variability of kinematic (time to peak acceleration, duration of acceleration phase, time to peak deceleration) and EMG (duration of agonist burst, duration of antagonist burst, time to antagonist burst) timing parameters decreased with increments of average velocity in a manner consistent with the variable timing error. In addition, the coefficient of variation for peak acceleration, peak deceleration, and integrated EMG of the agonist burst followed the same trend. Increasing average movement velocity also led to decreases in premotor and motor reaction times. Overall, the findings suggest a strong coherence between the variability of response outcome, kinematic, and EMG parameters.     

Response Timing Variability

A detailed kinematic and electromyographic (EMG) analysis of single degree of freedom timing responses is reported to (a) determine the coherence of kinematic and EMG variability to the reduced timing error variability exhibited with amplitude increments within a given criterion movement time and (b) understand the temporal organization of various movement parameters in simple responses. The data reveal that the variability of kinematic (time to peak acceleration, duration of acceleration phase, time to peak deceleration) and EMG (duration of agonist burst, duration of antagonist burst, time to antagonist burst) timing parameters decreased with increments of average velocity in a manner consistent with the variable timing error. In addition, the coefficient of variation for peak acceleration, peak deceleration, and integrated EMG of the agonist burst followed the same trend. Increasing average movement velocity also led to decreases in premotor and motor reaction times. Overall, the findings suggest a strong coherence between the variability of response outcome, kinematic, and EMG parameters.     

Developing motor planning over ages

Few studies have explored the development of response selection processes in children in the case of object manipulation. In the current research, we studied the end-state comfort effect, the tendency to ensure a comfortable position at the end rather than at the beginning of simple object manipulation tasks. We used two versions of the unimanual bar transport task. In Experiment 1, only 10-year-olds reached the same level of sensitivity to end-state comfort as adults, and 8-year-olds were less efficient than 6-year-olds. In each age group, children’s sensitivity did not increase during a session: i.e., either clearly showed the sensitivity or showed no sensitivity at all. Experiment 2 replicated these results when the bar was replaced by a pencil and when the task did not require much precision. However, when the task required more precision, 8-year-olds increased their level of sensitivity to the end-state comfort effect, whereas this was not the case for younger children. These results describe the development of advanced planning processes from 4 to 10 years of age as well as the positive effect of task constraints on the end-state comfort effect for 8-year-olds.     

Integrating velocity,time, and distance information: A developmental study

The development of understanding the relationships between velocity, time, and distance was investigated in three tasks. In each task, values of two dimensions were given, and 5-year-olds, 10-year-olds, and adults had to infer values of the third dimension. These inferences were made in all age groups. The integration rules were found to depend upon age and task. In the distance = time × velocity task, all age groups obeyed the normative multiplication rule. In the time = distance ÷ velocity task, the two older age groups obeyed the normative division rule, but the 5-year-olds shifted to a simpler subtraction rule. In the velocity = distance ÷ time task, which was the most difficult, the two older age groups simplified to use of a subtraction rule, and the 5-year-olds simplified even further to use of a distance-only rule. The knowledge level revealed for young children contrasts sharply with results from previous studies using Piagetian choice tasks, which apparently investigate selective attention to one dimension rather than conceptual understanding of relations.     

Pushing the limits of task difficulty for the right and left hands in manual aiming

The effects of task difficulty on the performance of the two hands in right-handers were examined in a manual-aiming paradigm. In order to examine both simple and complex tasks, movement amplitude, cursor size, and target size were manipulated, resulting in eight different indices of difficulty (as defined by Fitts' Law). Kinematic parameters examined included reaction time, movement time, time to and time after peak velocity, peak velocity, and resultant accuracy. Analysis revealed no differential effects of task difficulty on the overall movement times of the two hands. These results are discussed in light of current theories of manual asymmetries.     

Error processing in pointing at randomly feedback-induced double-step stimuli

Two experiments were conducted to determine the spatial and temporal organization of the arm trajectory in human subjects as they pointed to single- and double-step target displacements. Subjects pointed either without (Experiment 1) or with (Experiment 2) vision of their moving hand throughout the trial. In both experiments, target perturbation occurring in double-step trials was clearly perceived by the subjects and was randomly introduced either at the onset or at peak velocity of hand movement. Regardless of whether or not visual reafference from the pointing hand was available, subjects corrected the trajectory of their moving hand to accommodate the double-step. Moreover, asymmetrical velocity profiles were observed for responses to both types of target, with or without vision of the moving hand. The acceleration phase was a fixed pattern independent of the type of step stimulation. However, a clear dissociation, both in the deceleration phase and accuracy of responses to double-step targets, emerged according to the timing of target perturbation. When targets were perturbed at the onset of hand movement, subjects modulated the deceleration phase of their response to compensate for 88 to 100% of the second target displacement. In contrast, when targets were perturbed at peak velocity of hand movement, subjects were unable to modulate the deceleration phase adequately and compensated for only 20 to 40% of the perturbation. These results suggest that motor error is dynamically evaluated during the acceleration phase of a movement toward a perturbed target, allowing amendments to the trajectory to be performed during the deceleration phase. This main corrective process appears to be basically independent of visual reafference from the moving hand.     

Kinematics of Goal-Directed Arm Movements in Neglect: Control of Hand Velocity

Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional pointing movements to visual targets presented at body midline, the left and right hemispace. A group of healthy adults and a group of patients with right-hemispheric brain damage but no neglect served as controls. Pointing was performed under normal room light or in darkness. Time-position data of the hand were recorded with an opto-electronic camera system. We found that compared to healthy controls, movement times were longer in both patient groups due to prolonged acceleration and deceleration phases. Tangential peak hand velocity was lower in both patient groups, but not significantly different from controls. Single peak, bell-shaped velocity profiles of the hand were preserved in all right hemispheric patients and in three out of five neglect patients. Most important, the velocity profiles of neglect patients to leftward targets did not differ significantly from those to targets in the right hemispace. In summary, we found evidence for general bradykinesia in neglect patients, but not for a direction-specific deficit in the control of hand velocity. We conclude that visual neglect induces characteristic changes in exploratory behavior, but not in the kinematics of goal-directed movements to objects in peripersonal space.     

How do children coordinate simultaneous upper and lower extremity tasks? The development of dual motor task coordination

When performing simultaneous clapping with walking or galloping, adults adopt coupled, consistent and stable dual motor task coordination; do developmental trends in this coordination exist? In this study, we measured and compared coupling characteristics, consistency across trials and variability of phasing in 4-, 6-, 8-, and 10-year-olds (n=44) as they also performed the same dual motor task. For walk/clap, children adopted specific coupling patterns like adults by 8 years and with the same consistency by 10 years. Across age, children became less variable in clap and step movements separately and as coupled together. In the gallop/clap, children did not resemble adults in coupling patterns by 10 years but all measures were becoming more consistent across age. We discuss dual motor task coordination as a function of age and task complexity using a "dynamic" perspective within a developmental context.     

Visual control of manual aiming movements in 6- to 10-year-old children and adults

Recent results indicate that adults modulate their initial movement impulse toward a stationary visual target by processing visual afferent information. The authors investigated whether the mechanisms responsible for those modulations are already in place in young children or develop as the children grow older. Adults (n = 10) and 6-, 8- and 10-year-old children (ns = 6, 7, and 7, respectively) performed a video-aiming task while vision of the cursor they were moving was (acquisition) or was not (transfer) visible. The results indicated that within-participant variability of the initial impulse trajectory of the children's aiming movement leveled-off in acquisition between peak extent deceleration and the end of the initial impulse, whereas it increased linearly as movement unfolded in transfer. The results also indicated that children modulate their initial movement impulse when visual afferent information is available, although to a lesser extent than adults do, and strongly imply that contrary to past suggestions, the initial impulse of an aiming movement is not ballistic.     

Controlling velocity in rapid movements

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.     

Real-time manipulation of visual displacement during manual aiming

This study examined the spatial and temporal limitations of the visual corrective process in the control of upper limb movements. Real-time calculation of kinematic data was used to trigger a prismatic displacement of the movement environment during manual aiming. Using an OptoTrak motion tracking system, a data acquisition unit, and a custom-made program, perturbations were triggered at peak acceleration, peak velocity, and the estimated time of peak deceleration. Movement outcome was significantly influenced only when the visual displacement occurred at peak acceleration. The results support models of visual control that posit that early visual information is required for accurate limb control.     

Enhanced saccadic control in young people with Tourette syndrome despite slowed pro‐saccades

Tourette syndrome (TS) is a neurodevelopmental disorder characterized by motor and vocal tics. Tics are repetitive and uncontrolled behaviours that have been associated with basal ganglia dysfunction. We investigated saccadic eye movements in a group of young people with TS but without co‐morbid ADHD. Participants performed two tasks. One required them to perform only pro‐saccade responses (pure pro‐saccade task). The other involved shifting, unpredictably, between executing pro‐ and anti‐saccades (mixed saccade task). We show that in the mixing saccade task, the TS group makes significantly fewer errors than an age‐matched control group, while responding equally fast. By contrast, on the pure pro‐saccade task, the TS group were shown to be significantly slower to initiate and to complete the saccades (longer movement duration and decreased peak velocity) than controls, while movement amplitude and direction accuracy were not different. These findings demonstrate enhanced shifting ability despite slower reflexive responding in TS and are discussed with respect to a disorder‐related adaptation for increased cognitive regulation of behaviour.     

Relation between EMG activation patterns and kinematic properties of aimed arm movements

Aimed flexion movements of the arm of different amplitude and duration were studied. Velocity and acceleration traces of movements with equal duration but different amplitude were equal, apart from a scaling factor (ratio between movement amplitudes). After appropriate scaling, EMG activity of the first agonist burst for these movements superimposed. This was not true for EMG activity in the antagonist muscle. For movements with equal amplitude, but different duration, the time to peak acceleration was constant for all MT'. Except for this fact, traces of acceleration, velocity, and agonist activity following the time of peak acceleration were about equal after appropriate scaling in time and amplitude. The integral of EMG activity in the first agonist burst increased linearly with peak velocity. For the antagonist burst, the integrated EMG activity increased more than proportionally. During movements made as fast as possible, subjects used a different strategy by varying the duration of the accelerating phase for movements of different amplitude. Movement amplitude was achieved by adjusting the duration of the agonist burst and the onset time for the antagonist muscle. Amplitude of the antagonist burst was constant within a narrow range for movements of different amplitude. These results did not change when the inertial mass was doubled by loading the arm with an additional mass.     

Switching between tasks and responses: a developmental study

Task switching requires the ability to flexibly switch between task rules and responses, and is sensitive to developmental change. We tested the hypothesis that developmental changes in task switch performance are associated with changes in the facilitating or interfering effect of the previously retrieved stimulus-response (S-R) association. Three age groups (7-8-year-olds, 10-12-year-olds and 20-25-year-olds) performed a two-choice reaction time (RT) task in which spatially compatible or incompatible responses were required. The RT costs associated with switching between tasks were larger when responses were repeated than when responses were alternated. Younger children showed a greater cost than adults when switching between tasks but repeating responses. This age difference decreased when the interval between the previous response and the upcoming stimulus increased. Switch costs were larger when switching to the compatible task than to the incompatible task, but this effect did not differ between age groups. These findings suggest that young children build up stronger transient associations between task sets and response sets, which interfere with their ability to switch to currently intended actions. A similar pattern has previously been observed for older adults (Mayr, 2001), suggesting a common contributor to task switching deficits across the life span.     

Changes in Movement Variables Associated With Transient Overshoot of the Final Position

Transient overshoot (TO), which is assessed as the distance between the movement amplitude and the final position, was measured in a series of rapid, discrete elbow flexion movements performed under different distance and loading conditions by 7 participants. A positive relationship was found between kinematic variables (peak velocity, peak acceleration and deceleration, and the symmetry ratio) and the magnitude of TO, particularly in short movements performed against a light load. The relationships between TO and electromyographic (EMG) variables were low and mainly insignificant. Thus, TO contributes to the variability of rapid, discrete movements and therefore should be taken into account as an additional parameter in studies of the scaling of movement variables with movement mechanical conditions. TO could also represent a consequence of mechanical properties of the single-joint system rather than an independently programmed primary submovement.