Motor strategies in lifting movements: a comparison of adult and child performance

The experiment compares the performances of children six to nine years old and adults in a simple, monoarticular lifting task. Overt behaviors, as described by the kinematic features of the movement, do not differ qualitatively in the two groups. The patterns of motor commands, as expressed by the electromyographic recordings, are however strikingly different. Adults plan the movement with a careful balance between agonist muscle activity and passive, viscoelastic forces, whereas children use both agonist and antagonist active forces. It is argued that the motor strategy adopted by adults depends upon an internal representation of the properties of the motor system and of the size/weight covariation in natural objects, and that this representation is not yet fully developed at nine years of age.     

Representation of anatomical constraints in motor imagery: mental rotation of a body segment

Classically, the mental rotation paradigm has shown that when subjects are asked to judge whether objects that differ in orientation are spatially congruent, reaction times increase with angular discrepancy, although some reports have shown that this is not always the case. Would similar results be obtained with realistic figures of body segments? In this work, the mental rotation of a hand attached to its forearm and arm in anatomically possible and impossible starting positions is compared with the mental rotation of a hammer. The main results show that reaction times increase monotonically with the angle of discrepancy for both stimuli and that the speed of rotation is higher for anatomically possible orientations in the case of the hand. Thus, mental rotation of body segments follows the same empirical rules as objects of another nature, and biomechanical constraints imposed to the motility of these segments can be considered as attributes of the mental representation.     

Motor Strategies in Lifting Movements

The experiment compares the performances of children six to nine years old and adults in a simple, monoarticular lifting task. Overt behaviors, as described by the kinematic features of the movement, do not differ qualitatively in the two groups. The patterns of motor commands, as expressed by the electromyographic recordings, are however strikingly different. Adults plan the movement with a careful balance between agonist muscle activity and passive, viscoelastic forces, whereas children use both agonist and antagonist active forces. It is argued that the motor strategy adopted by adults depends upon an internal representation of the properties of the motor system and of the size/weight covariation in natural objects, and that this representation is not yet fully developed at nine years of age.     

Development of visuomanual tracking in 5- to 9-year-old boys

Visuomanual sinusoidal tracking is investigated in 5- to 9-year-old children. The proportion of successful performances steadily increases with age, but adult proficiency is never attained even by those who can perform the task. Moreover, the progress in proficiency—as measured by systems analysis techniques—is not monotonic and suggests the presence of distinct stages in the development of visuomotor coordination. Qualitative analysis of unsuccessful performance demonstrates that failures cannot be ascribed only to insufficient motor coordination and emphasizes the role of cognitive and representational factors even in such a simple task.     

Association between biological markers of sickle cell disease and cognitive functioning amongst Cameroonian children

Background: Some of the major complications of sickle cell disease (SCD) occur in the brain and apart from overt stroke, patients also present with cognitive impairments. We sought to evaluate the prevalence of cognitive deficits as well as their biological predicting factors in young SCD patients in Cameroon.

Methods: The cognitive performances of Cameroonian SCD young patients were evaluated using a neuropsychological test battery assessing four domains of cognitive functioning (executive functions, attention, memory, and sensory-motor skills) previously adapted and normalized on healthy subjects in Yaoundé.

Findings: Up to 37.5% of the 96 SCD patients aged 6 to 24 years (M?=?13.5, SD?=?4.9) had mild-to-severe cognitive deficits. The cognitive deficits tend to increase with age. There was a significant effect of SCD on executive functions and attention, whereas SCD patients performed as well as controls on memory and sensory-motor skills tests. Structural equation models showed a significant association between (a) severe anemia and lower executive functioning, (b) low fetal hemoglobin levels and lower executive functioning and attention, (c) history of cerebrovascular accidents and lower performances in executive functioning, sensory-motor skills, and memory, (d) pathological electroencephalogram and lower attention, and (e) abnormal Transcranial Doppler and lower memory.

Conclusion: SCD patients in Cameroon presented a very high prevalence of cognitive deficits, with a specific impairment of executive functions and attention. Routine neuropsychological evaluation for early detection of cognitive deficits in SCD patients could represent a cost-effective tool to implement in resource-limited contexts such as in sub-Saharan Africa.     

Sequential pointing in children and adults

The development of visuomotor control in sequential pointing was investigated in 6- to 10-year-old children and in adults. In 3 experiments we manipulated task difficulty by changing the number, the size, and the spacing of the targets in the sequences. In Experiment 4, only 1 movement was required; we varied independently the distance between targets and the distance of the starting point from the participant's body. Children's temporal and spatial parameters of the motor sequences showed large age-dependent trends, but did not reach the adult values. Comparison of performance across levels of difficulty and ages suggests that motor development is not a uniform fine-tuning of stable strategies. Instead, we argue that each stage of development is best characterized by the set of strategic components potentially available at that stage, and by the (age-dependent) rules for the selection of components in a given context.     

Clinical assessment of motor function: a processes oriented instrument based on a speed-accuracy trade-off paradigm

In this study, we developed a digitizing tablet-based instrument for the clinical assessment of human voluntary movements targeting motor processes of planning, programming and execution. The tool was used to investigate an adaptation of Fitts' reciprocal tapping task [10], comprising four conditions, each of them modulated by three indices of difficulty related to the amplitude of movement required. Temporal, spatial and sequential constraints underlying the various conditions allowed the intricate motor processes to be dissociated. Data obtained from a group of elderly healthy subjects (N=50) were in agreement with the literature on motor control, in the temporal and spatial domains. Speed constraints generated gains in the temporal domain and costs in the spatial one, while spatial constraints generated gain in the spatial domain and costs in the temporal one; finally, sequential constraints revealed the integrative nature of the cognitive operations involved in motor production. This versatile instrument proved capable of providing quantitative, accurate and sensitive measures of the various processes sustaining voluntary movement in healthy subjects. Altogether, analyses performed in this study generated a theoretical framework and reference data which could be used in the future for the clinical assessment of patients with various movement disorders, in particular Parkinson's disease.