Experiments in learning by imitation - Grounding and use of communication in robotic agents

Social behaviour and in particular social learning are key mechanisms for the cohesion and evolution of primate societies. Similarly, social skills might be desirable for artificial agents who are expected to interact with other natural or artificial agents. We view learning, communication and imitation as important capabilities to possess by social artificial agents and study how these skills can be designed and used by physically embodied autonomous robots. We study grounding and use of communication among heterogeneous agents. In particular, we investigate the role of social interactions for sharing of context and building of joint attention among communicative agents. Grounding and use of communication is investigated through simulations within a group of autonomous agents. Results show that social behaviour benefit the agents in two circumstances: (1) agents capable of following one another, and in this way imitating each other's movements, develop faster and better a common understanding of the language; (2) furthermore, the agents' capability of communicating with one another via a common vocabulary benefits to the group and to each agent individually as it speeds up the transmission of information. We use a connectionist model, based on Hebbian associative learning, for the learning of the word-signal pairs. This work follows robotic experiments [6, 5, 7] in which a physical autonomous robot was taught a vocabulary to describe its perceptions of objects, movement, inclination and orientation. The robot was taught either by a human instructor or by another robot. The teacher-learner robot experiments were based on an imitative strategy whereby the learner robot followed the teacher robot. The work of this paper demonstrates scaling up of this movement imitative strategy for transmitting a vocabulary across a group of robotic agents, i.e. from a teacher agent to several learner agents. In particular, it shows that imitative behaviour is necessary for the grounding of the agents' proprioceptions and speeds up the grounding of exteroceptions. These studies stress the importance of behavioural social mechanisms in addition to general cognitive abilities of associativity for grounding communication in embodied agents. In particular, it shows that a simple movement imitation strategy is an interesting scenario for the transmission of a language, as it is an easy means of getting the agents to share a common context of perceptions, which is a prerequisite for a common understanding of the language to develop. It is thus suggested that a behaviour-oriented approach might be more appropriate than a pure cognitivist one which is dominating in related studies of the mechanisms involved in grounding communication.