With the growing of information technologies in all everyday life situations, interactions with virtual agents are now common. Furthermore, we know that people's emotions influence interactions between them. In this thesis, we consider the case of unconstrained and expressive walk to study the influence of emotions on interactions between two real walkers. Then, we focus on the interactions between a virtual expressive human and a real subject. The first step of this work was to design and validate an experimental protocol allowing the analysis of unconstrained and expressive walks. Thus, we captured the motion of two actors walking alone and walking together. In the second part, we studied the data from the group walk situation and we highlighted the emergence of a leader-follower behavior between the walkers. We also showed that the characteristics of the emotions (eg dialogue) have an influence on this kind of synchronization. Last and not least, we studied the influence of emotions on interactions between a virtual human and a real one. We used a three-step process : creation and analysis of a database of expressive walks along a line between two walkers ; validation of the database through a perceptual study ; animation of a virtual human with the data from the database and analyze of the walk between real subjects and the virtual human. Results showed a strong similarity between the two situations.
