Abstract : Drawing on the study of the process involved in advertising messages creation, the article focuses on the relevance of social psychology in analysing the production of the medias communication. A qualitative investigation shows that in order to create a message, the designers engage in a dialogue in their working memory using "intra-psychic voices", representing, in this case, six actors of the advertising production dialogue. Through the analyzis of involved representations, we establish that the process of creation, which is iterative, structures reasoning procedures which are inductive, deductive and analogical as well as automatic and heuristic. The creative process also calls on the mental imagery which is activated at the same time as sensory-motor acts of manual graphic production. The process finishes with a phase in wich the copywriter rationalizes, with hindsight, his aesthetic and semiotic choices, bearing in mind the advertiser's requirements.