The task of bouncing a ball on a racket was adopted as a model system for investigating the behavioral dynamics of rhythmic movement, specifically how perceptual information modulates the dynamics of action. Two experiments, with sixteen participants each, were carried out to definitively answer the following questions: How are passive stability and active stabilization combined to produce stable behavior? What informational quantities are used to actively regulate the two main components of the action-the timing of racket oscillation and the correction of errors in bounce height? We used a virtual ball-bouncing setup to simultaneously perturb gravity (g) and ball launch velocity (v b) at impact. In Experiment 1, we tested the control of racket timing by varying the ball's upward half-period t up while holding its peak height h p constant. Conversely, in Experiment 2, we tested error correction by varying h p while holding t up constant. Participants adopted a mixed control mode in which information in the ball's trajectory is used to actively stabilize behavior on a cycle-by-cycle basis, in order to keep the system within or near the passively stable region. The results reveal how these adjustments are visually controlled: the period of racket oscillation is modulated by the half-period of the ball's upward flight, and the change in racket velocity from the previous impact (via a change in racket amplitude) is governed by the error to the target.

We design a personalized human-robot environment for social learning for individuals with autism spectrum disorders (ASD). In order to define an individual's profile, we posit that the individual's reliance on proprioceptive and kinematic visual cues should affect the way the individual suffering from ASD interacts with a social agent (human/robot/virtual agent). In this paper, we assess the potential link between recognition performances of body/facial expressions of emotion of increasing complexity, emotion recognition on platforms with different visual features (two mini-humanoid robots, a virtual agent, and a This is one of several papers published in Autonomous Robots comprising the "Special Issue on Assistive and Rehabilitation human), and proprioceptive and visual cues integration of an individual. First, we describe the design of the EMBODI-EMO database containing videos of controlled body/facial expressions of emotions from various platforms. We explain how we validated this database with typically developed (TD) individuals. Then, we investigate the relationship between emotion recognition and proprioceptive and visual profiles of TD individuals and individuals with ASD. For TD individuals, our results indicate a relationship between profiles and emotion recognition. As expected, we show that TD individuals that rely more heavily on visual cues yield better recognition scores. However, we found that TD individuals relying on proprioception have better recognition scores, going against our hypothesis. Finally, participants with ASD relying more heavily on proprioceptive cues have lower emotion recognition scores on all conditions than participants relying on visual cues.

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The aim of the study was to investigate the development of a rhythmical skill of children aged from 5 to 12 years old. Five age groups (5–6, 7–8, 9–10, 11–12, and young adults) performed a virtual ball bouncing task (16 forty-second long test trials). Task performances, racket oscillation, ball-racket impacts as well as the ball-racket coupling were analysed. The results showed a change in both performance and behaviour at the age of 7 years old. Before this age, children exhibited restricted perceptual-motor coordination with a high frequency of racket oscillation and a poor level of performance. After the age of 7, cycle-to-cycle adaptive coordination based on visual information was progressively acquired leading to increasing performance levels with age. Overall these results revealed a rapid change in capability to perform the ball bouncing task across age with a late emergence of the required coordination and significant change in the coordination at the age of 7.