Sarah Cummins-Sebree

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.

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.

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.

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 hammers 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. Childrens 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.

Change Blindness in Teams: Are Three Pairs of Eyes Better than One?

Several studies have indicted that people often fail to detect changes in visual displays under a variety of conditions. More recent research has indicated that individual operators are susceptible to change blindness in military command and control environments. Change blindness has been studied extensively but only at the individual level. Very little research has explored change blindness in the context of team performance. The purpose of this experiment was to determine if teams were more or less susceptible to change blindness than individual observers in the context of a simulated military command and control situation display. Individuals and teams monitored flicker sequences of displays containing 6, 12, 24, or 48 icons for changes in icon position. Our results revealed a team advantage but this effect was more pronounced when teams communicated. Communicating teams outperformed both non-communicating teams and individuals. However, communicating teams were not immune to change blindness but team communication played a key role in reducing change blindness and the workload associated with the change detection task.

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.