[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.

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.

[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.

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.

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.

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.

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.

Development of anticipatory orienting strategies during locomotor tasks in children.

Some basic problems related to the development of goal-directed locomotion in humans are reviewed here. A preliminary study is presented which was aimed at investigating the emergence of anticipatory head orienting strategies during goal-directed locomotion in children. Eight children ranging from 3.5 to 8 years had to walk along a 90 degrees right corner trajectory to reach a goal, both in light and in darkness. The instantaneous orientation in space of the head, trunk, hips and left foot antero/posterior axes was computed by means of an ELITE four-TV camera, 100 Hz system. The results showed that predictive head orienting movements can occur also in the youngest children. The head starts to rotate toward the goal before the corner point of the trajectory is reached. In children, the head peak rotation coincides with the trajectory corner while in adults the peak is attained before. In children, the walking speed is largely decreased in darkness. The results suggest that feedforward control of goal-directed locomotion appears very early in gait development and becomes increasingly important afterwards.

Hip stabilization and lateral balance control in toddlers during the first four months of autonomous walking.

The main purpose of the present paper was to investigate the inter-segmental coordinations between hip, shoulder and head, in toddlers, during the first four months of autonomous walking. The efficiency of locomotor balance control was examined in the frontal plane. The main result to emerge from this study is that the hip stabilization in space appears as soon as the first week of autonomous walking, while shoulder stabilization in space appears to be effective only at the second month. Finally, no preferred head stabilization, either in space or on shoulders, has appeared by the end of the fourth month. These results seem to indicate, from an early hip stabilization, an ascending progression with age of the ability to control lateral balance during locomotion.

Cross-correlation analysis of the lateral hip strategy in unperturbed stance.

Subjects standing heel-to-toe on either hard ground or soft support were instructed to stand upright keeping optimal balance. Lateral accelerometric measurements at head, hip and ankle levels were subjected to conjugate cross-correlations analysis in order to determine the co-ordinated movements or strategies. The results strongly suggest that there exists a hip lateral strategy which is very similar to the hip strategy previously described in fore-aft body oscillations. This lateral hip strategy was only observed when the greatest body oscillations were observed, namely on the soft supporting surface, and its descending sequence of co-ordinated movements is consistent with the idea of a top-down organization of postural control during movement or difficult stance conditions.

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.

Discrete visual samples may control locomotor equilibrium and foot positioning in man.

The static or dynamic visual cues required for equilibrium as well as for foot guidance in visually guided locomotion in man were studied using a variety of locomotion supports and illumination and visual conditions. Stroboscopic illumination (brief flashes) and intermittent lighting (longer flashes) were used to control and to vary the visual sampling frequency of static (positional/orientational) visual cues. There were three main findings: First, visual control of foot positioning during locomotion over a narrow support depends mainly upon the availability of high frequency static visual cues (up to about 12 Hz); and third, static visual cues required for equilibrium control are extracted from both the peripheral and the central visual field. Assuming that discrete demands for feedback occur, a simple probabilistic model was proposed, according to which the mean time that elapses following presentation of static visual cues about positions or changes of position accounts for the differences in the difficulty of the various illumination conditions.

Organization of lateral balance control in toddlers during the first year of independent walking.

The authors of the present study tested the hypothesis that toddlers initiate lateral body stabilization first at the hip level in order to better control the center of gravity (CG), minimize the upper body destabilization induced by the movement of the feet, and prevent falls. Intersegmental coordination among the hip, the shoulder, and the head was investigated in toddlers during their 1st year of independent walking. The efficiency of locomotor balance control was examined in the frontal plane. An automatic optical TV image processor (ELITE system) was used in analyzing the kinematics of foot, hip, shoulder, and head rotations. For the hip, the shoulder, and the head, appropriate anchoring indices were defined so that comparisons could be made concerning the stabilization of a given body segment with respect to its external space and to the adjacent supporting anatomical segment. Cross-correlation functions were also used for extracting the temporal patterns of the body segments that occurred during locomotion and for obtaining some information about the coupling of 2 consecutive segments such as the head-shoulder and the shoulder-hip. First, hip stabilization in space appeared from the 1st week of independent walking and clearly preceded those of the shoulder and the head, suggesting an ascending progression, with age, in the ability of new walkers to control lateral balance during locomotion. Second, the hip movements occurred before the shoulder movements and the shoulder movements before the head movements, indicating that locomotor balance control is organized temporally in an ascending fashion, from the hip to the head. Third, the high values of the correlation coefficients, mainly between the head and the shoulder, were consistent with a global en bloc operation of the head-trunk unit.

A statistical approach to sensorimotor strategies: conjugate cross-correlations.

A simple method, based on cross-correlation functions (CCFs) between two time series of kinematic or physiological measurements, is proposed for the analysis of multisegmental movements. Special emphasis is placed on measuring accelerations. When the movements of two body segments are coordinated but consistently time lagged, their CCF displays a peak at the corresponding time abscissa. The reproducible positions of the peaks reflect biomechanical or physiological constraints. Several significantly large peaks can be observed in a CCF. It is possible to identify coordinated movements involving more than two segments by applying simple rules of compatibility between the time lags and between the signs of the correlation peaks. With the method proposed, it is possible to determine the signs of relative variation and the time lags of the successive statistically correlated segmental movements. This is particularly useful in the case of both continuous and periodic sensorimotor control, where classical poststimulus methods cannot be applied. Unlike the classical poststimulus methods, this method does not require a time origin, and it is not necessary to monitor the muscles or even to specify exactly which ones are involved. The method is also applicable to experiments involving a time origin (e.g., and applied perturbation), although in this case it is less accurate than the averaging technique. Individual postural strategies can be identified, which suggests some interesting potential applications of the method to clinical studies.

Head-trunk coordination during hops using one or two feet in children and adults.

The main purpose of this study was to investigate the development of head-trunk coordination during single hops using one foot or two feet in children of two ages (5.5 to 6 and 7 to 7.5) and adults (n = 6/group). The kinematics of the subjects' hops were analyzed by means of an automatic optical TV-image processor called the ELITE system. The absolute angular dispersion of the head, trunk, and leg about the pitch and the roll axis were measured. Head and trunk pitch and roll anchoring indexes were calculated in order to compare the stabilization of a given segment with respect both to external space and to the underlying anatomical segment. Results were analyzed separately for 3 phases: take-off, flight, and landing. Only the last two phases, flight and landing, are presented in this paper, and the following was found: 1) During flight, under both unipedal and bipedal conditions, head and trunk stabilization in space about the pitch axis occurred in children as well as in adults, suggesting an articulated operation of the head-trunk unit. In contrast, during landing, in children and adults, head stabilization in space tended to disappear while trunk stabilization in space was still present, suggesting an en bloc operation of the head-trunk unit. Similarly, pelvis stabilization in space about the roll axis occurred in all subjects during both flight and landing under unipedal conditions, where lateral balance control is of primary importance. Taken together, these results suggest that head stabilization in space is phase dependent, while trunk stabilization is phase independent. The trunk, including the pelvis, may thus constitute a stable reference frame from which anteroposterior and lateral balance control is organized during hops. 2) For head-trunk coordination, whatever the component of rotation, the two groups of children differed from adults, but did not differ from each other, suggesting that, while jumping, the transition between 6 and 7 years of age in the organization of balance control takes place in the coordination of the lower limbs during the preparatory phase of the take-off.

Visual factors in the child's gait: effects on locomotor skills.

This kinematic study investigated the effects of visual factors on the angular oscillations of the head and trunk during various locomotor tasks in 3- to 8-yr.-old children and adults. The oscillations of the head under normal vision were limited and changed little across ages. Oscillations of both head and trunk about the roll axis were the most sensitive to difficulty in maintaining lateral equilibrium. On narrow supports, the lateral oscillations of the trunk increased between the ages of 3 and 6 years, with a maximum amplitude at the latter age and then decreased up to adulthood, suggesting a transition phase around the age of 6 years. Visual restriction had little effect on the control of angular oscillations of the head in children or adults. On a narrow support in darkness, adults increased oscillations of the trunk but reduced oscillations of the head. It can be concluded that, regardless of the age, control of locomotor equilibrium aims at limiting the angular oscillations of the head. Vision seems to contribute little to stabilization of the head.