Abstract
It is well-known that human social interactions generate synchrony phenomena which are often unconscious. If the interaction between individuals is based on rhythmic movements, synchronized and coordinated movements will emerge from the social synchrony. This paper proposes a plausible model of plastic neural controllers that allows the emergence of synchronized movements in physical and rhythmical interactions. The controller is designed with central pattern generators (CPG) based on rhythmic Rowat-Selverston neurons endowed with neuronal and synaptic Hebbian plasticity. To demonstrate the interest of the proposed model, the case of handshaking is considered because it is a very common, both physically and socially, but also, a very complex act in the point of view of robotics, neuroscience and psychology. Plastic CPGs controllers are implemented in the joints of a simulated robotic arm that has to learn the frequency and amplitude of an external force applied to its effector, thus reproducing the act of handshaking with a human. Results show that the neural and synaptic Hebbian plasticity are working together leading to a natural and autonomous synchronization between the arm and the external force even if the frequency is changing during the movement. Moreover, a power consumption analysis shows that, by offering emergence of synchronized and coordinated movements, the plasticity mechanisms lead to a significant decrease in the energy spend by the robot actuators thus generating a more adaptive and natural human/robot handshake.
Highlights
Physical and social interpersonal interactions induce gestural and verbal/non-verbal communications based on rhythmic mechanisms and rhythmic movements
The first originality of this article is to implement Hebbian mechanisms proposed by Righetti et al (2006), in a bio-inspired central pattern generators (CPG), which we previously used for biped locomotion (Nassour et al, 2014), enabling it to learn to synchronize with an external signal
On the contrary, when the system learns σs, we can see that σs adapts to each new frequency and we can observe that the torque and CPG output are synchronized and in phase (Figure 8)
Summary
Physical and social interpersonal interactions induce gestural and verbal/non-verbal communications based on rhythmic mechanisms and rhythmic movements. These mechanisms and the associated synchronization phenomena (limit cycles and clamping) could play a fundamental role in physical and social interpersonal interactions (Troje et al, 2006; Yonekura et al, 2012) and could be an emergent feature of the physical and social interactions between humans who adapt to each other and learn from each interaction, generating synchronization phenomena and creating conscious or unconscious links between people (Delaherche et al, 2012). CPGs endowed with plasticity rules allowing for synchronization with the control body (Shadmehr, 2010), are implied both in the generation of discrete and rhythmic movements (Grillner, 2006)
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