Sensitivity of Smoothness Measures to Movement Duration,Amplitude, and Arrests

ABSTRACT

Studies of sensory-motor performance, including those concerned with changes because of age, disease, or therapeutic intervention, often use measures based on jerk, the time derivative of acceleration, to quantify smoothness and coordination. However, results have been mixed: some researchers report sensitive discrimination of subtle differences, whereas others fail to find significant differences even when they are obviously present. One reason for this is that different measures have been used with different scaling factors. These measures are sensitive to movement amplitude or duration to different degrees. The authors show that jerk-based measures with dimensions vary counterintuitively with movement smoothness, whereas a dimensionless jerk-based measure properly quantifies common deviations from smooth, coordinated movement.     

Age-Related Differences in Locomotor Strategies During Adaptive Walking

Simultaneous control of lower limb stepping movements and trunk motion is important for skilled walking; adapting gait to environmental constraints requires frequent alternations in stepping and trunk motion. These alterations provide a window into the locomotor strategies adopted by the walker. The authors examined gait strategies in young and healthy older adults when manipulating step width. Anteroposterior (AP) and mediolateral (ML) smoothness (quantified by harmonic ratios) and stepping consistency (quantified by gait variability) were analyzed during narrow and wide walking while controlling cadence to preferred pace. Results indicated older adults preserved ML smoothness at the expense of AP smoothness, shortened their steps, and exhibited reduced stepping consistency. The authors conclude that older adults prioritized ML control over forward progression during adaptive walking challenges.     

Movement segmentation and visual perturbation increase developmental differences in motor control and learning

We examined the developmental differences in motor control and learning of a two‐segment movement. One hundred and five participants (53 female) were divided into three age groups (7–8 years, 9–10 years and 19–27 years). They performed a two‐segment movement task in four conditions (full vision, fully disturbed vision, disturbed vision in the first movement segment and disturbed vision in the second movement segment). The results for movement accuracy and overall movement time show that children, especially younger children, are more susceptible to visual perturbations than adults. The adults’ movement time in one of the movement segments could be increased by disturbing the vision of the other movement segment. The children's movement time for the second movement segment increased when their vision of the first movement segment was disturbed. Disturbing the vision of the first movement segment decreased the percentage of central control of the second movement in younger children, but not in the other two age groups. The children's normalized jerk was more easily increased by visual perturbations. The children showed greater improvement after practice in the conditions of partial vision disturbance. As the participants’ age increased, practice tended to improve their feedforward motor control rather than their feedback motor control. These results suggest that children's central movement control improves with age and practice. We discuss the theoretical implications and practical significance of the differential effects of visual perturbation and movement segmentation upon motor control and learning from a developmental viewpoint.     

Age-Related Changes in Smoothness of Gait of Healthy Children and Early Adolescents

Abstract

In this study, we acquired and processed trunk accelerations during level walking in 85 children aged 8-13?years to calculate spatio-temporal parameters and Harmonic Ratio (HR), which is a metrics representative of gait smoothness and step-to-step symmetry. The results show that while spatio-temporal parameters remain unchanged once normalized considering individuals’ anthropometry, significantly higher values of HR for both the antero-posterior and vertical directions were found in participants aged 12–13 with respect to those of 8–9. This indicates an improvement of gait symmetry, which suggests that the gait maturation process is still ongoing for the age ranges tested here.     

Using automated controlled rearing to explore the origins of object permanence

What are the origins of object permanence? Despite widespread interest in this question, methodological barriers have prevented detailed analysis of how experience shapes the development of object permanence in newborn organisms. Here, we introduce an automated controlled‐rearing method for studying the emergence of object permanence in strictly controlled virtual environments. We used newborn chicks as an animal model and recorded their behavior continuously (24/7) from the onset of vision. Across four experiments, we found that object permanence can develop rapidly, within the first few days of life. This ability developed even when chicks were reared in impoverished visual environments containing no object occlusion events. Object permanence failed to develop, however, when chicks were reared in environments containing temporally non‐smooth objects (objects moving on discontinuous spatiotemporal paths). These results suggest that experience with temporally smooth objects facilitates the development of object permanence, confirming a key prediction of temporal learning models in computational neuroscience.     

A Generalized Strategy for Measuring Performance in the Velocity-Position Phase Plane

Subjects pressed a key down as fast as possible but controlled the response duration of the keypress. The task required long (300 ±100 msec) and short (150±50 msec) durations in both simple (long only or short only) and choice (mixed long and short) conditions. Choice reaction time was slower than simple reaction time, but reaction time for long and short durations did not differ significantly for either simple or choice conditions. This finding fails to support a study by Klapp, Wyatt, and Lingo (1974) which found reaction time differences between long and short durations for choice but not simple conditions.