Visuo-motor coordination in 8-year-old children born pre-term before and after 28 weeks of gestation.

PURPOSE: This study compared the visuo-motor abilities between pre-term and full-term children. METHODS: Twenty-three 8-year-old children participated, five being born under 28 weeks gestational age (wGA) referred to as Preterms1 (mean=8 years 5 months [SD 0.3]), nine Preterms2 of 28-35 wGA (mean=7 years 9 months [SD 0.7]) and nine typically developing full-term controls (mean=8 years 6 months [SD 0.7]). All children were studied in an interhemispheric transfer time and in a visuo-manual pointing-task to test motor programming time in three conditions: unimanual pointing (dominant, non-dominant hands), mirror bimanual pointing (same direction for both hands) and opposite bimanual pointing. RESULTS: Significant differences were detected between Preterms 1 and 2, the latter being similar to controls. Preterms1 presented increases in interhemispheric time, suggesting an alteration in the transcallosal pathways. Programming time was significantly lengthened (p50.01) for dominant hand unilateral pointing and opposite bilateral pointing and it was the shortest for mirror pointing. CONCLUSIONS: A faulty programming of visuo-manual tasks is suspected in Preterms1 with potential difficulty inhibiting the non-dominant limb mirror movement. This may result from an impaired interhemispheric inhibition owing to potential corpus callosum thinning. Such measures may be used to help follow-up subtle changes in fine motor control and detect pre-terms at risk of developing long-term deficits.

Age-related differences in the reaching and grasping coordination in children: unimanual and bimanual tasks.

This study examined age-related differences in the coordinative mechanism of the reach-to-grasp movement in three groups of children aged 6, 8, and 11 year, and in healthy adults. Three prehension conditions were manipulated: an unimanual and a bimanual self-driven tasks in which the reaching and grasping of the object were performed by participants, and a bimanual externally-driven task, in which the experimenter brought the object into the vicinity of the participant which grasped it. Classical kinematics data-peak velocities of the reaching and the grasping, the time to onset grip opening, maximum grip opening and grip closure-were calculated. Moreover, to obtain equivalent kinematics variables for all age groups, relative time to peak velocity (% of reaching duration), relative maximum grip opening (% of object size), and percentage of the four types of phase plans between reaching velocity and grip size have been calculated for each group of age. Our main results showed (1) a high variability at age 6, (2) an age-related change between the 6- and 8-year old for almost all of the dependent variables, and (3) a significant difference between the 11-year olds and adults. In summary, at 6 years, the interdependence between the reaching and grasping programs was unstable. A transitory feedback-based coordination between reaching and grasping appeared at 8 years of age. Finally, the adults' relationship between reaching and grasping was not attained at the age of 11.

Updating of an internal model without proprioception: a deafferentation study.

This study sought to determine whether intact proprioception is required to adapt to a novel kinematic environment. We compared adaptation with a rotated visual feedback between a deafferented patient and healthy participants. They performed reaching movements towards visible targets while vision of the cursor was rotated by 30 degrees with respect to hand position. The patient adapted at the same rate and to the same extent as the controls when exposed to the rotated visual feedback. She also presented large aftereffects following removal of the perturbation. This suggests that proprioception is not an absolute requirement to update a kinematic internal model. Adaptation was likely mediated by a comparison between the sensory consequences of a movement as predicted by a forward model and the visual feedback from that movement.

Role of proprioceptive information in movement programming and control in 5 to 11-year old children.

The role of proprioceptive inputs in the control of goal-directed movements was examined, by means of the tendon vibration technique, in 5 to 11-year old children performing a serial pointing task. Children pointed, with movements of various amplitudes and at various positions, by alternating wrist flexions and extensions. Tendon vibration was applied to both agonist and antagonist muscles to perturb relevant muscular proprioceptive inputs during the static or dynamic phase of the task, i.e., during stops on targets or during movement execution. Constant and variable amplitude errors as well as constant position error were evaluated. Vibratory perturbation applied during movement execution resulted in a similar reduction in movement amplitude, yielding an increased constant error in all age groups and a systematic position error in the direction of the movement starting point. Perturbing proprioception during static phases preceding movement resulted in an age-related increase in the variable amplitude error, which was maximal in 5-year old children performing extension movements. The results were interpreted in terms of the use of proprioceptive information in the feedforward and feedback based components of movement control in children. In particular, the results indicated (1) developmental changes in the relative weighting of each component, (2) an increased capacity to move from one strategy to the other, depending on the availability of information, and (3) developmental changes from an alternated to an integrated control of amplitude and position in serial pointing.

Acquisition of visuomanual skills and improvement of information processing capacities in 6- to 10-year-old children performing a 2D pointing task.

The aim of this study was to investigate motor performance and visuomanual control through the analysis of Fitts' law in 6-, 8-, and 10-year-old children and adults performing a constrained two-dimensional pointing task. Participants were required to point and click on targets appearing on a laptop computer screen with a standard computer mouse. Three sizes of targets were used to create different indexes of difficulty. Analysis first showed linear visuomanual abilities to perform bi-dimensional pointing movements. It appears that developmental motor performance changes are due to combined enhanced programming processes and online feedback processing. Immature visuomanual control of 10-year-old children could be explained by higher cognitive requirements related to the task. As predicted by Fitts' law, movement time linearly decreases with the enlargement of target width. Moreover, a regression analysis of movement time on index of difficulty (ID) clearly showed significant differences for cognitive processing capacities with age: increasing ID effects are more dramatic in younger children performing computer mouse pointing movements.

Contribution of the cerebellum to self-initiated synchronized movements: a PET study.

Positron emission tomography (PET) was used to examine the neural substrate underlying self-initiated versus externally triggered synchronized movements. Seven healthy subjects performed synchronized right index finger and foot movements in two conditions: either by setting them going at their own pace (self-initiated condition) or by reacting to randomly dispensed auditory signals (externally triggered condition). In addition, subjects either self-initiated or performed in reaction to an audible tone a sequence of finger and foot movements. We hypothesized that cerebellar activity would reflect the behavioural difference observed when hand and foot are self-initiated synchronously compared to when these movements are externally triggered. Consistent with early observations by one of us (Paillard 1948, Année Psychologique, pp 28-47), subjects exhibited a precession of finger initiation over foot dorsi-flexion in the externally triggered condition, and a precession of foot dorsi-flexion over finger onset in the self-initiated condition. In addition to the cortical areas already described in the literature as differently activated in self-initiated and externally triggered movements, we found, according to the research hypothesis, a prominent activation of the left postero-lateral hemi-cerebellum in self-initiated synchronized movements when compared to the externally triggered movements. No cerebellar activity was found for self-initiated sequence of hand-foot movements when compared to externally triggered sequence of hand and foot movements. We suggest that this cerebellar activity could be related to some motor timing processes specifically required by the self-initiated synchronized movements.

Age-related differences in the visual processes implied in perception and action: distance and location parameters.

The aim of the two present experiments was to examine the ontogenetic development of the dissociation between perception and action in children using the Duncker illusion. In this illusion, a moving background alters the perceived direction of target motion. Targets were held stationary while appearing to move in an induced displacement. In Experiment 1, 30 children aged 7, 9, and 12 years and 10 adults made a perceptual judgment or pointed as accurately as possible, with their index finger, to the last position of the target. The 7-year-old children were more perceptually deceived than the others by the Duncker illusion but there were no differences for the goal-directed pointing movements. In Experiment 2, 50 children aged 7, 8, 9, 10, and 11 years made a perceptual judgment or reproduced as accurately as possible, with a handle, the distance traveled by the target. Participants were perceptually deceived by the illusion, judging the target as moving although it was stationary. When reproducing the distance covered by the target, children were unaffected by the Duncker illusion. Our results suggest that the separation of the allocentric visual perception pathway from the egocentric action pathway occurs before 7 years of age.

Aged-related differences in the attentional cost of pointing movements.

The aim of the present study was to analyze, in children aged 6, 8 and 11, the developmental trend of the attentional cost related to the programming and execution of pointing movements, using a dual-task paradigm. Our results showed that the attentional cost associated to the programming and the first phase of the pointing movement decreased non linearly with age, in particular a plateau between 8 and 11 was observed. This confirmed that the developmental trend of the control of pointing movements is characterized by a no monotonic evolution in which feedforward processes were predominantly used in the younger children, feedback processes were predominantly used in older children (since age 8), and one-line over feedforward processes were used in adults.

Visuomanual coordination in childhood: adaptation to visual distortion.

The aim of the experiment was to study the adaptive capacities of children to perform drawing movements while being visually perturbed. Children aged 5-11 years and a group of adults drew diamonds via information provided through a computer screen. The screen display was either upright or rotated 180 degrees. Results showed that the absence of direct vision of the hand yielded more perturbation in the youngest group of children compared to all other groups. In spite of some initial difficulty, all children reached accurate control after five trials. When faced with spatial rotations of the visual field, youngsters were again more perturbed than others. All children showed the same rate of adaptation to visual rotations, but they differed on adaptive strategies. Five- and 7-year-olds shifted to a feedforward mode of control consisting of the production of a rapid gesture, followed by error evaluation in order to correct their next movement. Older children were characterised by a progressive integration of reafferent visual and proprioceptive information. It resulted in an increase in duration of strokes and reduced speed, meaning enhanced on-line retrieval of information. However, 9-year-old children experienced more difficulty recuperating sensory information during movement than 11-year-olds, and kept using error feedback. Finally, visuomanual coordination in children aged 11 years, while slightly differing from that of adults, was not yet totally mature.