Postural sway was assessed [via center of pressure (COP) 95% elliptical area (EA), path length (PL), normalized path length (PL(n)) and sample entropy (SEn)] in four conditions of bipedal upright stance [compliant (Foam) vs. non-compliant (Hard) with eyes-open (EO) vs. eyes-closed (EC)] prior to, and immediately following, a six-week balance training intervention in a group of healthy adults (N = 26). The intervention was comprised of nine exercises progressed in difficulty based on the subjective assessments of individual competency. Results showed that EA and PL were increased, while PL(n) and SEn were decreased, in EC and Foam stance conditions (collapsed across effects of balance training). Interpretations were that restricted vision and a compliant surface represented constraints to postural control that caused increases in the amount (PL) and area (EA) of sway, but decreases in its coordinative twisting/turning (PL(n)) and temporal complexity (SEn). It was argued that these changes might represent compensatory adaptations in effort to maintain postural control given the demands of the imposed constraints. Balance training caused no change to EA, but did result in decreased PL, PL(n), and SEn for stance conditions performed on the Foam (either EO or EC). These changes were interpreted to reflect improved postural control, potentially through the learned adoption of a more deterministic postural control strategy that is uniquely defined by the constraints imposed on upright stance by the compliant surface.

Children with autism spectrum disorder (ASD) demonstrate a host of motor impairments that may share a common developmental basis with ASD core symptoms. School-age children with ASD exhibit particular difficulty with hand-eye coordination and appear to be less sensitive to visual feedback during motor learning. Sensorimotor deficits are observable as early as 6 months of age in children who later develop ASD; yet the interplay of early motor, visual and social skill development in ASD is not well understood. Integration of visual input with motor output is vital for the formation of internal models of action. Such integration is necessary not only to master a wide range of motor skills, but also to imitate and interpret the actions of others. Thus, closer examination of the early development of visual-motor deficits is of critical importance to ASD. In the present study of infants at high risk (HR) and low risk (LR) for ASD, we examined visual-motor coupling, or action anticipation, during a dynamic, interactive ball-rolling activity. We hypothesized that, compared to LR infants, HR infants would display decreased anticipatory response (perception-guided predictive action) to the approaching ball. We also examined visual attention before and during ball rolling to determine whether attention engagement contributed to differences in anticipation. Results showed that LR and HR infants demonstrated context appropriate looking behavior, both before and during the ball’s trajectory toward them. However, HR infants were less likely to exhibit context appropriate anticipatory motor response to the approaching ball (moving their arm/hand to intercept the ball) than LR infants. This finding did not appear to be driven by differences in motor skill between risk groups at 6 months of age and was extended to show an atypical predictive relationship between anticipatory behavior at 6 months and preference for looking at faces compared to objects at age 14 months in the HR group.