Postural control development from late childhood through young adulthood.

BACKGROUND: The development of stable postural control is characterized by changes in sway variability and periods of rapid reorganization of motor system components. RESEARCH QUESTION: The current study examined whether changing biomechanical and perceptual demands influences the postural control behavior during development. METHOD: The center of pressure (COP) was assessed via a cross-sectional design. Data were collected from 48 females in three age groups (late childhood, mid-adolescence, and young adulthood) during four quiet stance conditions: (1) eyes open with feet apart, (2) eyes open with feet together, (3) eyes closed with feet apart, and (4) eyes closed with feet together. Linear measures included total path length of the COP and the mean/standard deviation of the overall COP position and speed. To characterize the sway patterns via nonlinear analyses, the speed and two-dimensional positional time series were submitted to sample entropy and Renyi entropy, respectively. RESULTS: The linear results indicated that the late childhood group displayed longer COP trajectories (p < .001) and faster and more variable COP speed (p's < .001). These results held for both the feet apart and feet together conditions, independent of vision. The nonlinear results indicated that the late childhood group exhibited less regularity, overall, in their COP sway position (i.e., Renyi entropy) compared to the two older groups in the feet apart condition (p's ≤ .041), and to the young adults in the feet together condition, independent of vision (p < .001). However, the mid-adolescent group demonstrated greater regularity in their COP speed (i.e., sample entropy) when their eyes were closed compared to the other two groups, independent of stance (p's < .05). SIGNIFICANCE: The linear results support previous findings, while the nonlinear measures indicate sway characteristics that may provide a window into the development of underlying control processes that regulate quiet standing.

Perception of another person's maximum reach-with-jump height from walking kinematics.

Humans can perceive affordances (possibilities for action) for themselves and others, including the maximum overhead height reachable by jumping (reach-with-jump height, RWJ). While observers can accurately perceive maximum RWJ for another person without previously seeing the person jump, estimates improve after viewing the person walk, suggesting there is structure in walking kinematics that is informative about the ability to produce vertical force for jumping. We used principal component analysis (PCA) to identify patterns in human walking kinematics that specify another person's maximum RWJ ability, and to determine whether athletes are more sensitive than non-athletes to these patterns. Kinematic data during treadmill walking were collected and submitted to PCA to obtain loading values for the kinematic time series variables on the first principal component. Kinematic data were also used to create point-light (PL) displays, in which the movement kinematics of PL walkers were manipulated using the obtained PCA loading values to determine how changes in body-segment movements impacted perception of maximum RWJ height. While manipulating individual segmental loadings in the PL displays did not substantially affect RWJ estimates, PL displays created by replacing the PCA loadings of a high-jumper with those of a low-jumper, and vice versa, resulted in corresponding reversals of participants' RWJ estimates, suggesting that the global structure of walking kinematics carries information about another's maximum RWJ height. Athletes exhibited greater sensitivity than controls to the kinematic manipulations, indicating that they are better attuned to useful kinematic information as a result of their sport experience.

Ontogeny of tool use: how do toddlers use hammers?

Hammering with a hand tool appears early in life. Skillful hammering involves accommodating movements to properties of the hammer, orienting the hammer's head to the item to be struck, and maintaining stable posture during forceful action with the arm(s). We aimed to characterize development of these abilities in young children (12, 18, and 24 months old). Children struck at a peg with a hammer held in the hand or a hammer attached to a handle. Children struck more frequently with a hard hammer surface than a soft one, and more frequently (although less accurately) with handled hammers than with non-handled hammers. Developmental differences were evident in accuracy, number of strikes, and kinematic parameters, especially with the handled object. Children's ability to use objects for forceful and accurate percussion changed measurably over the second year, in tandem with improving postural stability and greater motion of the elbow.

Functional Task Constraints Foster Enhanced Postural Control in Children With Cerebral Palsy.

BACKGROUND: Postural instability is a classical characteristic of cerebral palsy (CP), but it has not been examined during functional play activity. Recent work has demonstrated that when motor tasks are made functionally more relevant, performance improves, even in children with movement pathology. It is possible that in a disease state, the underlying control mechanisms that are associated with healthy physiology must be elicited. OBJECTIVE: The study objective was to explore the utility of the functional play task methodology as a more rich and interpretable approach to the quantification of postural instability in children with CP. DESIGN: Postural stability measures obtained from a cross-sectional cohort of children with CP (n=30) were compared with stability measures taken from children with typical development (n=30) during a single measurement period. METHODS: Postural stability data were obtained with a portable force platform system. Postural sway was quantified during a precision manual functional play task. A baseline condition (no task) also was included. Postural sway variability and postural sway regularity were analyzed with analyses of variance. RESULTS: There was an apparent difference in postural control (greater irregularity, greater sway variability) during quiet stance between children with CP and peers with typical development; this difference was mitigated during the performance of the precision functional play task. LIMITATIONS: A small and nonprobability sample of convenience may limit the findings of this study. CONCLUSIONS: The findings illustrate flexibility and adaptability in the postural control system despite the pathological features associated with CP.

Children with cerebral palsy effectively modulate postural control to perform a supra-postural task.

The purpose of this study was to determine whether signatures of adaptive postural control remain present in children with cerebral palsy (CP) when they performed a supra-postural task (i.e., a task performed above and beyond the control of posture) requiring them to balance a marble inside a tube held in the hands. Measures of center of pressure (COP) dynamics (how regular or predictable were the COP data as quantified by the sample entropy metric) and variability (as quantified by the COP standard deviation) were obtained from a sample of children with CP (n=30) and compared to the same measures taken from typically developing (TD) children. Children with CP demonstrated an apparent inefficiency in postural control (greater irregularity, greater sway variability) relative to TD peers during a quiet-stance (no supra-postural task) condition (p<.05). During supra-postural task performance, those differences were attenuated, though they remained statistically different (p<.05). The findings illustrate flexibility and adaptability in the postural control system, despite the pathological features associated with CP.

Lower-limb proprioceptive awareness in professional ballet dancers.

Enhanced proprioceptive feedback strengthens synergistic muscle groups and stabilizes the coordination of limbs, thus contributing to the movement efficiency of ballet dancers. The present study compared lower-limb proprioceptive awareness in professional ballet dancers to matched controls who had no dance training. Two assessment methods were used to test the hypothesis that ballet dancers would demonstrate increased proprioceptive awareness in the ankle, knee, and hip: 1. a joint-position matching task to assess static proprioceptive joint awareness, and 2. an eyes-closed, quiet standing task to assess both static and dynamic proprioceptive awareness through measures of center of pressure (COP) variability. Results of the matching task indicated that the dancers exhibited greater proprioceptive awareness than controls for all three joints (p < 0.001). Also, dancers were equally aware of the positioning of their ankle, knee, and hip joints (p > 0.05), whereas controls were less aware of their ankle position compared to their knee and hip joints (p < 0.001). Measures indexing COP variability during quiet standing did not differ between groups and thus failed to reflect increased proprioceptive awareness in dancers (all p > 0.05). This indicates that quiet stance may have limited value as a means for evaluating proprioception. These findings provide preliminary evidence that enhanced proprioceptive awareness of lower limb joints should be considered as an evaluative criterion for dancers' ability to learn complex ballet skills. They also indicate that quiet standing tasks may not provide sufficient challenge for dancers' enhanced proprioceptive awareness to manifest.

Multi-segmental postural coordination in professional ballet dancers.

Ballet dancers have heightened balance skills, but previous studies that compared dancers to non-dancers have not quantified patterns of multi-joint postural coordination. This study utilized a visual tracking task that required professional ballet dancers and untrained control participants to sway with the fore-aft motion of a target while standing on one leg, at target frequencies of 0.2 and 0.6Hz. The mean and variability of relative phase between the ankle and hip, and measures from cross-recurrence quantification analysis (i.e., percent cross-recurrence, percent cross-determinism, and cross-maxline), indexed the coordination patterns and their stability. Dancers exhibited less variable ankle-hip coordination and a less deterministic ankle-hip coupling, compared to controls. The results indicate that ballet dancers have increased coordination stability, potentially achieved through enhanced neuromuscular control and/or perceptual sensitivity, and indicate proficiency at optimizing the constraints that enable dancers to perform complex balance tasks.

Perceiving affordances for joint actions.

Two individuals acting together to achieve a shared goal often have an emergent set of afforded behavioral possibilities that may not easily reduce to either acting alone. In a series of experiments we examined the critical boundaries for transitions in behavior for individuals walking through an aperture alone or alongside another actor as a dyad. Results from experiment 1 indicated that an intrinsically scaled critical boundary for behavioral transitions was different in individuals than in dyads performing a similar task. Experiment 2 demonstrated that observers are perceptually sensitive to the difference in action parameters for the dyad, while still maintaining perceptual sensitivity about the boundaries of action relative to individuals. In experiment 3, we determined that observers' perception of critical action boundaries for individuals and dyads has a similar informational basis (eye-height scaling). In experiment 4, we demonstrated that observers were able to perceive critical action boundaries for other dyads independently of membership. Together, these results suggest that individuals are sensitive to the affordances related to a joint action, and that this process may not entirely reduce to the perception of the affordances for each individual.

The production of bimanual percussion in 12- to 24-month-old children.

Bimanual coordination represents a complex self-organizing system that is subject to both internal and contextual constraints. Although there has been interest in examining bimanual development throughout the lifespan, few data exist relative to the bimanual activity of children between 1 and 4 years of age. The study reported here represents an initial effort to address this gap. Twenty-seven children who were either 12, 18 or 24 months old were videotaped while drumming with sticks on a plastic drum. Two independent observers recorded bout length as well as number and phase relation of movement cycles within bouts. Kinematic analysis provided more detailed information about the timing and form of children's activity. Results indicate that bimanual drumming becomes preferred over unimanual drumming by 2 years of age, that the proportions of different phase relations exhibited by children change between 1 and 2 years of age, and that the behavior appears to go through periods of stability and variability within this age range. These results are discussed in the context of the child's physical development and interactions with the environment during this period.

Choosing and using tools: capuchins (Cebus apella) use a different metric than tamarins (Saguinus oedipus).

Cotton-top tamarins (Saguinus oedipus) selected canes positioned so that a straight inward pull brought food within reach (M. D. Hauser, 1997; see also record 1997-41347-003). Tamarins failed to retrieve food with canes in other positions, and they did not reposition these canes. In this study, tufted capuchin monkeys (Cebus apella) preferred canes they could pull straight in when these were present, but they also repositioned canes in individually variable ways, and their success at obtaining food with repositioned canes improved with practice. In accord with predictions drawn from ecological psychology, capuchins discovered affordances of canes through exploratory actions with these objects, whereas tamarins did not. Ecological theory predicts these differences on the basis of species-typical manipulative activity, and it provides a useful approach for the study of species differences in tool-using behavior.

Relational spatial reasoning by a nonhuman: the example of capuchin monkeys.

The authors review spontaneous manipulation and spatial problem solving by capuchin monkeys to illuminate the nature of relational reasoning (wherein two or more elements of a problem or situation are considered together to arrive at a course of action) that these monkeys use in goal-directed activity. Capuchin monkeys master problems with one, two, or three spatial relations, and if more than one relation, at least two relations may be managed concurrently. They can master static and dynamic relations and, with sufficient practice, can produce specific spatial relations through both direct and distal action. Examining capuchins' spatial problem-solving behavior with objects in the framework of a spatial relational reasoning model leads to new interpretations of previous studies with these monkeys and other nonhuman animals. The model produces a variety of testable predictions concerning the contribution of relational properties to spatial reasoning. It also provides conceptual linkages with neurological processes and cognitive analyses of physical reasoning. Understanding relational spatial reasoning, including tool use, in a wider view is vital to informed, principled comparison of problem solving and the use of technology across species, across ages within species, and across eras in human prehistory.