Strength of the perception action coupling in human body discrimination tasks.

Perceiving and extracting information from others rely on functional Perception Action Coupling. Because motor experiences influence the strength of the perception action coupling, we explored the duality between vision and proprioceptive information about the self and others in body perception using a sequential same-different visual task from 6 to 7 years old to adults. Using a same-different matching task combined with congruent or incongruent action execution, this study explored in 30 children (M ± SD: 9.2 ± 1.5; 16♀), 33 adolescents (M ± SD: 14.7 ± 1.5; 16♀) and 28 adults (M ± SD: 29.5 ± 6.5; 12♀) how the congruence of the perception action coupling could influence the body representation building in memorizing and discriminating other's postures. The first result revealed better performances to perceive other's body postural changes compared to objects' shapes modifications as early as 6-7 years old. Nevertheless, this ability needs a long time to mature as reflected by the lower performances in children compared to older groups, i.e. adolescents and young adults. In addition, executing a congruent action during the encoding phase increased the RT, reflecting involvement of additional cognitive processes of self-other correspondence, without improving the performance accuracy, due to a slow maturation of multimodal body representations. On the other hand, executing an incongruent action during the encoding phase revealed an interference effect to perceive others' posture, demonstrated by the decrease of performance accuracy. As we initially hypothesized, the strength of perception action coupling appears to be modulated by age. Indeed, the interference effect had a greater impact in adolescents involved in a different judgment of two body postures. Therefore, the assessment of the perception action coupling may predict the body representation maturity in typical development or internal body representation dysfunction in neurodevelopmental disorders.

Body schema building during childhood and adolescence: a neurosensory approach.

In order to perceive and act in its environment, the individual's body and its interactions with the sensory and social environment are represented in the brain. This internal representation of the moving body segments is labeled the body schema. Throughout life, body schema develops based on the sensory information used by the moving body and by its interactions with the environment including other people. Internal representations including body schema and representations of the outside world develop with learning and actions throughout ontogenesis and are constantly updated based on different sensory inputs. The aim of this review is to present some concepts and experimental data about body schema, internal representations and updating process during childhood and adolescence, as obtained using a neurosensory approach. From our developmental studies, it was possible to explore the slow maturation of the sensorimotor representations by examining the anticipatory control. By manipulating proprioceptive and visual information, which are at the heart of the construction of body schema, we wished to highlight notable differences between adolescents and young adults on both a postural and perceptual level, which confirms the late maturation of multisensory integration for central motor control.

Updating process of internal models of action as assessed from motor and postural strategies in children.

The objective of this study was to investigate the updating process of internal models of action in children and young adults, through the postural and motor strategies adopted in simple tasks, namely sit-to-stand (STS) and back-to-sit (BTS). To this end, 11 healthy children from 7 to 10years (latest stage of childhood) and 12 healthy adults participated in the experiment. The STS and BTS tasks were performed with horizontal support surface and support surface tilted 10° to the right or forward in order to investigate the immediate adaptation of the internal representations of the movement. Movement variables that included the durations of STS and BTS and the amplitudes of the trunk movement were computed. Postural characteristics were also considered during the transition from STS to BTS, including the trunk orientation and the head stabilization strategies. Despite certain similarities with adults, especially in terms of the asymmetry of the performance times for the two tasks (STS vs. BTS) and the partial movement adaptations, the children were less able than adults to adapt both postural and movement controls to the new support conditions. Thus, it appears that the updating of internal models of action is a process that matures slowly throughout ontogenesis.

Development of action representation during adolescence as assessed from anticipatory control in a bimanual load-lifting task.

The aim of this study was to explore, during adolescence, alterations in the use of a sensori-motor representation as unveiled by the measurement of anticipatory postural control in a bimanual load-lifting task. We hypothesised that adolescence constitutes a period of refinement of anticipatory postural control due to on-going updates of the body schema and sensori-motor representations. The anticipatory postural control was assessed using a bimanual load-lifting paradigm in which subjects stabilise their left postural forearm, which is supporting an object, while they use their right hand to lift up the object. Kinematics and electromyographic data were recorded in two groups of adolescents (11-13 and 14-16 years of age) and a group of adults. Age and gender effects were tested. During voluntary unloading, the postural forearm stabilisation in adolescents was still different from the adult one, suggesting that further improvement of the postural forearm stabilisation must take place after the age of 16. No differences occur in the two adolescent groups. Moreover, girls presented a better stabilisation of the postural forearm than boys, indicating an earlier refinement of anticipatory postural control. The decrease of activity over postural flexors, which ensure postural stabilisation, appeared later in adolescents with respect to adults. Delayed timing adjustments and increased variability could reflect intense developmental processes underlain by an intense period of CNS maturation during adolescence. We discuss the role of brain maturation in the refinement of sensori-motor representations and the update of body schema.

Extreme short-term environmental constraints do not update internal models of action as assessed from motor imagery in adults.

According to the simulation theory, the internal simulation of a movement (imagined movement, IM) and its execution (actual movement, AM) are based on the same motor representations. The brain uses these representations for controlling action. The specific objective of this study was to investigate the updating process of internal models of action in adults, through massive environmental changes involved by microgravity (0G). 0G has multiple effects on motor control, including short-term adaptations with respect to the planification and performance of actions. However, the effects of 0G on internal representations of action are still largely unknown. To address this issue, thirteen subjects performed first sit-to-stand (STS) and back-to-sit (BTS) tasks, and subsequently had to imagine movement performance in these tasks. The tasks were performed under normogravity (1G) and 0G conditions. Based on durations of actual and IMs, two main results emerged from this study. In 1G, actual and IM's durations were similar. However, in 0G, AM durations were significantly longer than IM durations. Furthermore, IM durations in 0G were similar to the 1G value. These results show that although the planification and execution of action were immediately adapted to the 0G condition, the storage of afferent information was inadequate to recalibrate the predictive model. These results suggest that sudden change in gravity was not considered for updating internal models of action, and that forward model probably required more practice in order to integrate the modification of the sensorial feedback generated by the new environmental constraints.

[Understanding social interaction in children with autism spectrum disorders: does whole-body motion mean anything to them?]. / Compréhension des interactions sociales chez des enfants atteints de troubles du spectre de l'autisme : le langage du corps leur « parle ¼-t-il ?

BACKGROUND: Autism spectrum disorders (ASD) are characterized by difficulties in social interaction and verbal and non verbal reciprocal communication. Face and gaze direction, which participate in non verbal communication, are described as atypical in ASD. Also body movements carry multiple social cues. Under certain circumstances, for instance when seeing two persons from far, they constitute the only support that allows the grasping of a social content. Here, we investigated the contribution of whole-body motion processing in social understanding. OBJECTIVE: The aim of the study was to evaluate whether children with ASD make use of information carried by body motion to categorize dynamic visual scenes that portrayed social interactions. METHODOLOGY: In 1973, Johansson devised a technique for studying the perception of biological motion that minimizes static form information from the stimulus, but retains motion information. In these point-light displays, the movement figure, such as a body, is represented by a small number of illuminated dots positioned to highlight the motion of the body parts. We used Johansson's model to explore the ability of children with ASD to understand social interactions based on human movement analysis. Three-second silent point-light displays were created by videotaping two actors. The two actors were either interacting together or moving side by side without interacting. A large range of social interaction displays were used to cover social scenes depicting social norms (conventional gestures and courteous attitudes), emotional situations (carrying positive or negative valences) and scenes from games (sports, dance, etc.). Children were asked to carefully watch the stimuli and to classify them according to the question "Are the two persons communicating or not?". Four sessions of 3 minutes were performed by each child. Children with ASD were compared with typically developing control children matched with either non verbal mental age or chronological age. Response and reaction time were recorded in this force-choice categorization task. RESULTS: The performance of children with ASD suggested that they were able to extract a social content from body motion. However, they were significantly less efficient than typically developing control children, either matched for non verbal mental age or chronological age. This was especially the case for the social interaction displays. Neither impaired global perceptual processing, nor cognitive development, nor emotional content could explain these lower performances. DISCUSSION AND CONCLUSION: The results are discussed in the context of an action representation deficit and a dysfunction of the mirror mechanism in ASD. In conclusion, this behavioural study highlights the potential of point-light displays as a rehabilitation tool in ASD.

Action and representation of action during childhood and adolescence: a functional approach.

Our scientific activity is focused on the field of action and representation of action from various adaptative situations during the life span, including pathology and extreme environment such as microgravity. The early action/perception matching, subserving the motor simulation network, is probably a major milestone for the building of action and representation of action during the course of ontogenesis. We have developed a functional approach of motor development based on a gradual mastering of coordination, adaptation and anticipation in postural control in the course of ontogenesis from babies to adolescents. This functional approach is recently associated with studies of brain structures involved in action and representation of action in children and adolescents with typical or atypical neurodevelopment. From our developmental studies, it was possible to put in light two turning points during motor development, such as 6/7 years of age and adolescence. The first step for children consists in building a repertoire of postural strategies. The second step consists in learning to select postural strategy depending on the characteristics of the task and the environmental requirements. An appropriate selection means to anticipate the consequence of the movement in order to maintain balance control and efficiency of the task. Taking into account the complexity of the parameters to control and the late maturation of anticipation and representation of action, it is not surprising that the development of postural control continues up to late periods during childhood and adolescence.

[Developmental and locomotor disorders in children]. / Développement et troubles de la marche chez l'enfant.

From one year of age, gait and balance disorders are frequent complaints in neurology. During the first year following the acquisition of independent walking, most of the gait, such as transition from digitigrade to plantigrade locomotion, parameters are well-established in children. Nevertheless, bipedal locomotion means solving a large number of balance problems. Locomotor balance needs many years to mature in the course of ontogenesis. From various gait analysis, it was possible to establish a repertoire of locomotor strategies used in typical and pathological development. The last part of this paper is devoted to the possible responses that can be proposed for gait and balance disorders occurring during childhood.

[Postural study on healthy subjects during experimental vocal effort]. / Etude posturale de sujets normaux en situation expérimentale d'effort vocal.

INTRODUCTION: The objective of the study was to assess how posture and vocal acoustics are modified when one needs to communicate despite environmental obstacles (i.e. vocal effort performance). METHOD: 20 healthy young women participated to this study. They had to communicate numbers to a listener. Environmental obstacles were the distance between the subject and the auditor, and the noise. Segmental posture modifications were recorded and analyzed using the numerical infra-red system for movement analysis SMART. Vocal acoustics and electroglottography were also recorded and analyzed using the EVA system. RESULTS: The study showed the presence of objective postural modifications during vocal effort. Their amplitude increased when the environmental obstacles to communications increased, and they anticipated the vocal production. DISCUSSION: The vocal effort concept and its relation with the posture, the voice and the subject's feeling are reviewed on the basis of these results. Laryngeal effort is not isolated, but belongs to a global behavioral strategy which aims to improving the efficiency of the communication.

Proprioceptive contribution of postural control as assessed from very slow oscillations of the support in healthy humans.

Maintaining erect human posture depends on graviceptive information. This can come from at least of three origins: vestibular, visual and somaesthetic. We hypothesize here that subject's use proprioception rather than visual or vestibular cues for their control of upright body posture and this even when subjects stand on a tilting body support surface. In order to find experimental evidence for this hypothesis, we exclude in our experiments visual cues (eyes close) and by keeping frequency and amplitude of the tilt stimulus so low that it would be below the detection threshold for vestibular semi-circular canal stimuli. The orientations of body segments were analysed during various phases of the perturbation cycle. Segmental stabilisations were defined in terms of both the global anchoring index calculated during the whole perturbation cycle and an appropriate sequential anchoring index calculated during various phases in the perturbation cycle. We show that subjects tend to align their bodies with the space vertical and do so better for their heads than for their upper bodies and lower bodies. A further finding is that stabilisation is related to the tilt stimulus in the form that it is minimal at the turning points of the tilt, where peak tilt velocity is minimal with the sinusoidal stimulus used. These finding suggest first that proprioceptive cues are predominant in the control of body orientation in quasi-static condition and second that the head and trunk stabilisation strategies used as the basis of postural control depend on the properties of the moving support.

Postural control and sensory integration in cervical dystonia.

OBJECTIVE: Postural control and sensory integration were assessed in 12 patients with Cervical Dystonia (CD) and 11 healthy control subjects (CS), who were asked to maintain their posture as vertical as possible with their eyes open and closed while standing on a platform tilting laterally at angular accelerations below the vestibular activation threshold. METHODS: Data were collected with a three-dimensional acquisition system. The orientation and stabilization components were studied using specific indexes. We also tested the subjective visual vertical. RESULTS: CD does not affect whole body postural control. CD patients were able to control the orientation of their head. CS stabilized their head in space, especially when their eyes were open. This head stabilization strategy was lost in the CD patients, and the presence of visual inputs made no difference. CD patients seemed to neglect the visual information when controlling their head. The RFT confirmed this visual independence. CONCLUSION: CD patients seem to ignore the sensory information skewed by the disease: their reference segment shifts from head to trunk and they tend to preferentially use proprioceptive information. SIGNIFICANCE: As the proprioceptive chain remains functional in CD patients, it seems likely that the vestibular system might rather be involved in the pathophysiology of CD.

Impaired vertical postural control and proprioceptive integration deficits in Parkinson's disease.

The aim of the present study was to investigate how the orientation and stabilization components of postural control may be affected as the result of the impaired proprioceptive integration possibly occurring in Parkinson's disease. To determine the proprioceptive contribution to postural control, parkinsonian patients and control subjects were asked to maintain vertical stance while very slow sinusoidal oscillations were being applied in the lateral and antero-posterior planes to the platform on which they were standing. The amplitude and frequency of their movements were kept below the semicircular canal perception threshold. Data were collected with the ELITE automatic motion analyzer and the two postural components (orientation and segmental stabilization) were analyzed at head and trunk levels while the subjects were performing the task with their eyes open and closed. The results show that 1) the parkinsonian groups' performances were affected in terms of both the postural orientation and stabilization components in comparison with the control group, 2) the use of vision improved the parkinsonian patients' postural performances, and 3) both parkinsonian patients and control subjects achieved better postural performances when antero-posterior perturbations rather than lateral perturbations were applied to the foot support. These results suggest that Parkinson's disease is associated with proprioceptive impairment, which may be an important factor contributing to these patients' postural deficits. On the basis of these results, the visual dependence observed in parkinsonian patients is re-defined as an adaptive strategy partly compensating for the impaired proprioception.

Axial rotation in Parkinson's disease.

AIMS: To investigate the ability of patients with Parkinson's disease to perform a rotation around the longitudinal axis of the body. Three questions were raised. Is body rotation impaired in Parkinson's disease? Is there a level of the kinematic chain from the head to the foot at which the impairment is more severe? Is the deficit related to the general slowness of movement in Parkinson's disease? METHODS: Kinematic data were recorded. The temporal organisation of body rotation during gait initiation was analysed in 10 patients with Parkinson's disease, who were all at an advanced stage of the disease and had all experienced falls and freezing during their daily life, and in five controls. The latency of the onset of the rotation of each segment was measured by taking the onset of the postural phase of step initiation as reference value. Locomotor variables were also analysed. RESULTS: Body rotation was found to be impaired in patients with Parkinson's disease, as the delay in the onset of the rotation of each segment is greater than that in controls. Moreover, a specific uncoupling in the onset of shoulder and pelvis segment rotation was seen in patients. This impairment of rotation is not related only to the general slowness of movements. CONCLUSION: Patients with Parkinson's disease were found to have an impairment of posturo-kinetic coordination and impaired capacity to exert appropriate ground reaction forces to orient the pelvis in space.

[Vocal forcing and posture: experimental studies on normal subject]. / Forçage vocal et posture : études expérimentales chez le sujet sain.

UNLABELLED: One of the well-known characteristics of vocal forcing is postural with an increase in the antero-posterior movements of the trunk and head during phonation. OBJECTIVE: we conceived different physiological experiments on normal subjects to explore in an objective way these movements. MATERIALS AND RESULTS: A series of experiments using a platform of posturography confirmed that there is an increase in the tensions in the muscles implied in the posture when the subject forces his voice because of an ambient noise. This increase is characterized by the index VCOP rms (variance of the displacement of the center of pressure in upright position) which passes from 13.19 in normal voice to 18.63 in forced voice. A complementary study was carried out with an equipment of analysis of the movements (ELITE). CONCLUSION: We could, thus, confirm the existence of the contemporary antero-posterior movements of vocal forcing. The discussion concerns the application perspectives of these experimental knowledge in the clinical field of the dysfunctional dysphonia.

Goal directed locomotion and balance control in autistic children.

This article focuses on postural anticipation and multi-joint coordination during locomotion in healthy and autistic children. Three questions were addressed. (1) Are gait parameters modified in autistic children? (2) Is equilibrium control affected in autistic children? (3) Is locomotion adjusted to the experimenter-imposed goal? Six healthy children and nine autistic children were instructed to walk to a location (a child-sized playhouse) inside the psychomotor room of the pedopsychiatric centre located approximately 5 m in front of them. A kinematic analysis of gait (ELITE system) indicates that, rather than gait parameters or balance control, the main components affected in autistic children during locomotion are the goal of the action, the orientation towards this goal and the definition of the trajectory due probably to an impairment of movement planning.

Voluntary head stabilisation in space during oscillatory trunk movements in the frontal plane performed before, during and after a prolonged period of weightlessness.

The ability to voluntarily stabilise the head in space exhibited by two subjects during lateral rhythmic oscillations of the trunk has been investigated before, during and after a prolonged period of microgravity (microG) exposure. In flight acquisitions were performed onboard the Core Module of the Russian Space Station MIR as part of the T4 "Human Posture in Microgravity" experiment of the 179-days ESA-RKA mission EUROMIR-95. Data collection and kinematic analysis were performed by means of a space-qualified version of the automatic motion analyser ELITE. Head stabilisation in space strategy was estimated by means of the head anchoring index and cross-correlation analysis. Results show that head orientation may be well stabilised about the roll axis both with and without the presence of visual information. This was true despite the expected reduction in vestibular efficiency and muscular proprioception occurring in-flight. In one subject, however, vision was found to improve head stabilisation in space post-flight, presumably to recover from the postural deficiency induced by the long-term microG exposure. Head stability during trunk movements was achieved with either over-compensatory (out-of-phase), under-compensatory (in-phase) or mixed movement strategies, as was attested by the analysis of cross-correlation functions between head and shoulder movements. In weightlessness, vision occlusion seemed to influence the choice of the strategies to be used as well as the reduction of movement variability. The feedforward nature of compensatory head movements suggests that head stabilisation could be based in weightlessness on the internal postural body scheme, supposed to be adapted to the weightless environment within 5 months of microG exposure.

Development of postural adjustment during gait initiation: kinematic and EMG analysis.

The authors studied the development of postural adjustments associated with the initiation of gait in children by using kinematic and electromyographic (EMG) analysis. Participants (N = 28) included infants with 1-4 and 9-17 months of walking experience, children 4-5 years of age, and adults. Anticipatory postural adjustments (APA) were present in the youngest age groups, including a clear anticipatory lateral tilt of the pelvis and the stance leg, which enabled the child to unload the opposite leg shortly before its swing phase. An anticipatory activation of the hip abductor of the leg in stance phase prior to heel-off was found, suggesting pelvis stabilization. APA did not appear consistently until 4-5 years of age. A decrease in segmental oscillations occurred across the ages, indicating better control of intersegmental coordination in the frontal and sagittal planes during the postural phase of gait initiation. Young walkers presented APA involving movements of both the upper and the lower parts of the body, whereas, like adults, 4- to 5-year-olds were able to laterally shift only the pelvis and the stance leg. The oldest children and the adults also showed lower activation levels of hip and knee muscles but higher activation at the ankle level. Those kinematic and EMG results taken together suggest a clear developmental sequence from an en bloc operation of the body through an articulated operation with maturation, walking experience, or both.

Development of anticipatory postural adjustments in a bimanual load-lifting task in children.

Anticipatory postural adjustments (APA) are needed to perform a movement without perturbing posture. We investigated the development of APA in 3- to 4-year-old children during a bimanual load-lifting task. The task required maintaining a stable elbow position despite imposed or voluntary unloading of the forearm. Although children can compensate the consequences of unloading by using APA, their performance did not reach an adults' level. In addition, children showed high intra-individual variability in the voluntary situation, revealed by the coexistence of both adult-like and immature patterns in kinematic and electromyographic data. In conclusion, the present study reports that APA, associated with a bimanual load-lifting task, are still being set up in 3- to 4-year-old-children. The intra-individual variability should decrease with age and be associated with a progressive mastering of the timing parameters characterizing APA.

Body orientation and control of coordinated movements in microgravity.

The present paper focuses on the organization of posture and movement under normal and microgravity conditions. Two reference values subserving the control of erect posture and the performance of movements are analyzed. The first is 'geometrical' in nature and corresponds to the orientation of a body segment with respect to the external world. The second reference value, which involves the mass and inertia of the body segments, is the position of the centre of mass with respect to the foot support area. The reorganization of these parameters which occurs under microgravity is discussed in the framework of a hierarchical model of posture. Suggestions are made for training procedures which could be used to prevent loss of balance from occurring in astronauts on landing after long space flights.

Development of locomotor balance control in healthy children.

A set of experimental studies showing how inter-segmental coordination develops during childhood in various locomotor tasks is reviewed. On the basis of these results and two functional principles (stable reference frame and control of the degrees of freedom of the body joints), we recently proposed an ontogenetic model for the sensorimotor organization of balance control in humans (5). In this model, the hypothesis was put forward that the two main modes of equilibrium control (ascending vs descending temporal organization) operate alternatively and are associated with either of two modes of head-trunk linkage ('en bloc' vs articulated) during four successive periods in the course of ontogenesis. The advantage of this model is that it is heuristic and therefore open to further improvements, including the generalization of these balance strategies to most of the posturo-kinetic activities, the comparison between unperturbed natural balance and reactions to postural disturbances. Some improvements are suggested, and are illustrated by the studies of intersegmental coordination in new experimental tasks such as hops using one foot or two feet and the initiation of gait. These new results are consistent with the idea that mastery of the degrees of freedom to be controlled simultaneously during the movement improves gradually with age. Moreover, they support the concept of multiple reference frames which operate in a complementary manner or in concert to permit the most appropriate organization of balance control, depending on the environmental requirements.