How important is body language in mood induction procedures with a humanoid robot?

The aim of this article is to investigate the effectiveness of the body language of a humanoid robot to induce emotions. It is based on the principles of positive psychology (PP), social learning, therapeutic robotics and mood induction procedures (MIPs). According to the Velten Method to induce a positive mood, the body language of a humanoid robot is used here as a modulated variable to test its efficacy inducing emotions. We have three hypotheses: (H1) Positive body language reinforces the positive attitude of the Velten positive statements; (H2) Body language which expresses the opposite attitude that the one expressed by Velten statements, that is a negative attitude, can vary negatively the mood induction results; (H3) The more positive the body language is, the higher the positive induction effect is; We have run experiments with 48 volunteers to test these hypotheses. Results show that the hypotheses (H1) and (H2) are correct, but it is not the case for (H3), which is not confirmed with an exaggerated expression of elated mood. Furthermore, our new combined MIP has a significant effect size to induce positive emotions.