Synchrony is claimed by psychology as a crucial parameter of any social interaction: to give to human a feeling of natural interaction, a feeling of agency [17], an agent must be able to synchronise with this human on appropriate time [29] [11] [15] [16] [27]. In the following experiment, we show that synchrony can be more than a state to reach during interaction, it can be a useable cue of the human's satisfaction and level of engagement concerning the ongoing interaction: the better is the interaction, the more synchronous with the agent is the human. We built an architecture that can acquire a human partner's level of synchrony and use this parameter to adapt the agent behavior. This architecture detects temporal relation [1] existing between the actions of the agent and the actions of the human. We used this detected level of synchrony as reinforcement for learning [6]: the more constant the temporal relation between agent and human remains, the more positive is the reinf...