Chaotic exploration and learning of locomotion behaviours

We present a general and fully dynamic neural system, which exploits intrinsic chaotic dynamics, for the real-time goal-directed exploration and learning of the possible locomotion patterns of an articulated robot of an arbitrary morphology in an unknown environment. The controller is modeled as a network of neural oscillators that are initially coupled only through physical embodiment, and goal-directed exploration of coordinated motor patterns is achieved by chaotic search using adaptive bifurcation. The phase space of the indirectly coupled neural-body-environment system contains multiple transient or permanent self-organized dynamics, each of which is a candidate for a locomotion behavior. The adaptive bifurcation enables the system orbit to wander through various phase-coordinated states, using its intrinsic chaotic dynamics as a driving force, and stabilizes on to one of the states matching the given goal criteria. In order to improve the sustainability of useful transient patterns, sensory homeostasis has been introduced, which results in an increased diversity of motor outputs, thus achieving multiscale exploration. A rhythmic pattern discovered by this process is memorized and sustained by changing the wiring between initially disconnected oscillators using an adaptive synchronization method. Our results show that the novel neurorobotic system is able to create and learn multiple locomotion behaviors for a wide range of body configurations and physical environments and can readapt in realtime after sustaining damage

Chaotic exploration and learning of locomotor behaviours

Recent developments in the embodied approach to understanding the generation of adaptive behaviour, suggests that the design of adaptive neural circuits for rhythmic motor patterns should not be done in isolation from an appreciation, and indeed exploitation, of neural-body-environment interactions. Utilising spontaneous mutual entrainment between neural systems and physical bodies provides a useful passage to the regions of phase space which are naturally structured by the neuralbody- environmental interactions. A growing body of work has provided evidence that chaotic dynamics can be useful in allowing embodied systems to spontaneously explore potentially useful motor patterns. However, up until now there has been no general integrated neural system that allows goal-directed, online, realtime exploration and capture of motor patterns without recourse to external monitoring, evaluation or training methods. For the first time, we introduce such a system in the form of a fully dynamic neural system, exploiting intrinsic chaotic dynamics, for the exploration and learning of the possible locomotion patterns of an articulated robot of an arbitrary morphology in an unknown environment. The controller is modelled as a network of neural oscillators which are coupled only through physical embodiment, and goal directed exploration of coordinated motor patterns is achieved by a chaotic search using adaptive bifurcation. The phase space of the indirectly coupled neural-body-environment system contains multiple transient or permanent self-organised dynamics each of which is a candidate for a locomotion behaviour. The adaptive bifurcation enables the system orbit to wander through various phase-coordinated states using its intrinsic chaotic dynamics as a driving force and stabilises the system on to one of the states matching the given goal criteria. In order to improve the sustainability of useful transient patterns, sensory homeostasis has been introduced which results in an increased diversity of motor outputs, thus achieving multi-scale exploration. A rhythmic pattern discovered by this process is memorised and sustained by changing the wiring between initially disconnected oscillators using an adaptive synchronisation method. The dynamical nature of the weak coupling through physical embodiment allows this adaptive weight learning to be easily integrated, thus forming a continuous exploration-learning system. Our result shows that the novel neuro-robotic system is able to create and learn a number of emergent locomotion behaviours for a wide range of body configurations and physical environment, and can re-adapt after sustaining damage. The implications and analyses of these results for investigating the generality and limitations of the proposed system are discussed

Doing Duo - a case study of entrainment in William Forsythe's choreography "Duo"

Waterhouse E, Watts R, Bläsing B. Doing Duo - a case study of entrainment in William Forsythe's choreography "Duo". Frontiers in Human Neuroscience. 2014;8:812.Entrainment theory focuses on processes in which interacting (i.e., coupled) rhythmic systems stabilize, producing synchronization in the ideal sense, and forms of phase related rhythmic coordination in complex cases. In human action, entrainment involves spatiotemporal and social aspects, characterizing the meaningful activities of music, dance, and communication. How can the phenomenon of human entrainment be meaningfully studied in complex situations such as dance? We present an in-progress case study of entrainment in William Forsythe's choreography Duo, a duet in which coordinated rhythmic activity is achieved without an external musical beat and without touch-based interaction. Using concepts of entrainment from different disciplines as well as insight from Duo performer Riley Watts, we question definitions of entrainment in the context of dance. The functions of chorusing, turn-taking, complementary action, cues, and alignments are discussed and linked to supporting annotated video material. While Duo challenges the definition of entrainment in dance as coordinated response to an external musical or rhythmic signal, it supports the definition of entrainment as coordinated interplay of motion and sound production by active agents (i.e., dancers) in the field. Agreeing that human entrainment should be studied on multiple levels, we suggest that entrainment between the dancers in Duo is elastic in time and propose how to test this hypothesis empirically. We do not claim that our proposed model of elasticity is applicable to all forms of human entrainment nor to all examples of entrainment in dance. Rather, we suggest studying higher order phase correction (the stabilizing tendency of entrainment) as a potential aspect to be incorporated into other models

Feasibility of novel gait training with robotic assistance : dynamic entrainment to mechanical perturbation to the ankle

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 149-156).Rehabilitation of human motor function is an issue of the utmost significance, and the demand for the effective rehabilitation service is even growing with the graying of the population. Robotic technology has provided promising ways to assist recovery of the motor function of upper extremities. In contrast, current robotic therapy for lower extremities has shown inferior efficacy. In this thesis, the source of the limited efficacy of current robotic walking therapy is addressed. Essential mechanical components for robustly stable walking are identified as energy dissipation and proper compensation. Based on these essential components, design criteria of effective robotic walking therapy are suggested as foot-ground interaction and ankle actuation. A novel strategy of robot aided walking therapy reflecting the design criteria is proposed; dynamically entraining human gait with periodic ankle torque from a robot. Experiments with normal subjects and neurologically impaired subjects support the feasibility of the proposed rehabilitation strategy. The gait period of subjects entrain to the periodic mechanical perturbation with a measurable basin of entrainment, and the entrainment always accompanies phase-locking so that the mechanical perturbation assists propulsion. These observations are affected neither by auditory feedback nor by a distractor task for normal subjects, and consistently observed in impaired subjects. A highly simplified one degree of freedom walking model without supra-spinal control or an intrinsic self-sustaining neural oscillator (a rhythmic pattern generator) encapsulated the essence of these observations. This suggests that several prominent limit-cycle features of human walking may stem from peripheral mechanics mediated by simple afferent feedback without significant involvement of supra-spinal control or central pattern generator. The competence of the highly simplified model supports that the proposed entrainment therapy may be effective for a wide range of neurological impairments.by Jooeun Ahn.Ph.D

Expertise and training effects on co-ordination dynamics in a whole body rhythmical task

This research consists of two studies. The purpose was to investigate the effects of slow and fast music tempo on interjoint co-ordination variability in an aerobic stepping task. The \u27step knee-up\u27 task is a cyclical whole body movement performed on the step platform. The exercise consisted of a few repetitive cycles. A cycle was defined by eight counts, four counts for the left leg pattern and four for the right leg as follows: The first half of the cycle was counted: I. Step up with the left foot onto the 20-cm step platform, 2. Flex the right hip to bring the right knee up; 3. Step down to the floor with the right foot and, 4.Tap once with the left foot on the floor near the right foot. The second half of the cycle consisted of the following four counts: I. Step up onto the platform with the right foot; 2. Flex the left hip to bring the left knee up. 3. Step down to the floor with the left foot and, 4. Tap once with the right foot on the floor near the right foot. The participants were instructed to move both arms simultaneously forward and backward so that the limbs would perform in-phase movement, which is opposite to the natural anti-phase arm movements that accompanies walking and stepping activities. This pattern of the arm movements has been defined as a proposed pattern or the \u27to-be-learned\u27 pattern. In particular, the research examined to what extent unskilled and skilled participants would adjust their movement co-ordination to cope with changes in performance conditions in attempting to achieve the criterion task. In the first study, these effects were observed in novices and experts, while the effects of the fast tempo training on intrinsic dynamics (self-paced condition) were considered in the second study. Both studies were based on the Dynamic Systems Theory. The environmental factor, which was considered as the control parameter affecting performance in both studies, was the music tempo. In the first study interjoint co-ordination responses were analysed in terms of a version of the Haken, Kelso and Bunz\u27s (HKB) modal that considers detuning or frequency competition terms. Six novice and six expert females participated in the experiment performing a \u27step-knee-up\u27, a whole body rhythmical task, under different music tempos. They were tested at a slow tempo at 48 beat/min and at a fast tempo of 144 beat/min. Two hypotheses were proposed. Firstly, it was hypothesised that discrete relative phase variability of inter-joints co-ordination would be higher.at the fast tempo then at the slow tempo in both, novices and experts. It was further hypothesised that, in order to cope with changes in performance conditions and still achieve the criterion task, novices would demonstrate higher variability than experts at both the slow and fast tempo. Results showed that interjoint co-ordination in experts was more consistent (less variable) at both the slow and fast tempo compared to novices, in all couplings expect in the left leg. Furthermore, follow-up tests revealed that Tempo and Side effects in novices were not significant. In experts, however significant Side effect was found in shoulder joint coupling and hip-knee joint coupling. Higher variability was found in left leg interjoint coupling between hip and knee joints at both tempos, compared to the right leg. In shoulders joint coupling, however, higher variability was found only in the slow tempo for the right side observation of the L Shoulder-R Shoulder movement. Finally, it was observed that the initially specified arm movement direction (iso directional or in-phase movement) changed to anti-phase direction at fast tempo in novices. Therefore, in novices, in-phase arm movements were more sensitive to fast tempo perturbations compared to anti-phase. While these results may be in contrast to Haken, Kelso and Bunz\u27s model predictions they are partly supported by Whittal, Forester and Song\u27s (1999) findings. In the second study, whether practising the task under the fast music tempo would affect the interjoint co-ordination stability at the preferred tempo performance (without the music) was investigated. It was hypothesised that, after the training under the fast music tempo interjoint coupling variability at the preferred tempo would decrease. The hypothesis was partly accepted as variability decreased in the self- paced condition after training only in shoulder-shoulder interjoint couplings compared to the self-paced condition before training. Results in the second study were discussed in relation to Shaner and Kelso\u27s (1988) dynamical theory of environmental function and motor learning transfer principles. It was found that training under the fast tempo did not significantly affect overall performance at self-paced and fast tempos. However, different changes in interjoint co-ordination strength were observed in different couplings before and after training as the function of (the left or right) body side. It was concluded that interjoint co-ordination flexibility is highly specific to the interaction between the task, body side, performance condition and skill level. Finally it was suggested that an individual approach to the analysis of variability in co-ordination dynamics in skilled and unskilled performance and learning be considered