Cerebral palsy (CP) concerns 2 children out of 1000 in the general population (SCPE 2002). It is the main cause of postural and motor deficits in children.

During the past 20 years, the postural deficits exhibited by these children have been attributed to various factors :

1. neuromuscular functions
2. sensory integration
3. muscular-squeletic functions.

The common point of all these studies is the existence of immature motor patterns, probably related to an inability to implement more elaborated and adapted motor patterns with respect the task to perform.

CP children do not develop the characteristics of the plant grad locomotion. They exhibit a uniform muscular activation with a high level of co-activation. Locomotion is generally characterized by an increase of stretching reflexes at short latencies and by a low level of activation associated to a low modulation of gastrocnemius muscles..

These data also suggest that it is the control of the temporal rather than the spatial parameters of the head which are mainly altered in CP children.

Even though static postural control and locomotion are considered as automatic processes, this control requires, however, a significant amount of attentional resources.

Within this context, the amount of attentional resources which need to be solicited can provide information on two complementary dimensions. On one hand, on the level of automaticity of postural control and/or locomotion when subjects' attention is oriented toward another task. On the other hand, on the cognitive cost of postural control and/or locomotion, depending on children age, that is, as a function of their level of maturation and of the nature and importance of their sensory-motor deficits. When the amount of required attentional resources is reduced, postural control and/or locomotion is considered as automatic processes with a low cognitive cost.

The dual task paradigm in which subjects have to simultaneously process a cognitive (e.g. Stroop task) and a postural or motor task (e.g., standing upright on a force platform) is generally used to investigate these questions.

How an appropriate allocation of attention is performed as a function of the cognitive and postural/motor tasks is important in the developmental process of posture and locomotion. It seems to be even more crucial in CP children and more generally in pathology.

The main goal of the present project is to investigate the contribution of attentional processes in postural control and locomotion of CP children as compared to control healthy children.

Within this scientific and clinical context, we hypothesize:

• That CP children will be less stable than healthy children (in control situation) and that the attentional cost for controlling static posture will be higher.
• On the basis of Olivier et al.'s work (2008) showing in adults and children aged 4 to 11 that postural control is better when attention is oriented toward a video film (i.e., decrease of the attentional demand allocated to the control of static posture), we predict that CP children will be more stable in dual task situation with visual or sound distractors than when focusing attention on postural control alone.
• We also predict that an additional cognitive task (adapted Stroop task), by increasing the attentional demand, will induce a deficit of postural control confirming Reilly et al.'s results (2008b).

On the same basis, we will also investigate the attentional cost of locomotion.

Exploratory study of dynamic equilibrium during locomotion in the same conditions.

Investigation of posture in the following conditions:

1. without attentional distractors and without additional cognitive task (control condition)
2. with attentional visual and sound distractors (video film)
3. with sound attentional distractor alone (sound track of the video film)
4. with an additional cognitive task (Stroop task adapted for children).

Considering the goals of this research project, no serious undesirable event is expected to occur. However, falls may occur accidentally while rising or descending from the force platform, during static posture, or during locomotion. Consequently, in addition to the experimenter, a physiotherapist or someone of the medical staff will be present during all experimental recordings.

The environment will be also organized to the secure the experimental room by excluding all potentials dangerous or non necessary objects. Whenever necessary, the potentials falls will be reported and declared to the health authorities.

Inclusion Criteria:

• CP children with postural and/or motor deficits due to early cerebral deficits (from conception to 2 years of age according to G. Tardieu) non hereditary and non evolutionary.
• Aged 7 to 12 years because before 7 years of age the range and speed of postural control exhibit a great variability and after 12, our eligibility criteria are not standardized
• presenting a clinical CP diplegia or hemiplegia (cf. EMGF),
• able to stand upright without assistance for at least (real recording time of 30 sec during the experiment) on a force platform (L 50 cm x l 50 cm x h 4,4 cm) and to walk straight ahead on a walking track (518 cm long x 90 cm wide and 0,5 cm thin) without assistance,
• without severe visual or hearing deficit (>0,3 for the worse eye without correction or hearing loss <70db for the worse ear without correction) as indicated in the personal medical report
• without hyperactivity trouble (Conners' questionnaires non significant <70), without major attentional deficits (images matching test), without denomination troubles (ELOLA test), able to perform dual tasks (Tea-ch test).

Exclusion Criteria:

• parents' or children' informed consent rejected,
• Participation to another biomedical experiment during this study,
• Children unable to control upright posture without assistance for at least 45 sec on a force platform (L 50 cm x l 50 cm x h 4.4 cm) or unable to walk without assistance
• Absence of social security coverage.