Abstract : In the present work, we try to provide some understanding about the factors underlying the directional tendencies, by examining the impact of biomechanical constraints and cultural habits on directionality in graphic movements. French and Syrian subjects, children and adults, were compared in six experiments in order, to put in evidence the cognitive and psychomotor differences caused by the fact that the Eastern and Western cultures oppose on the directionality of writing and reading habits, and that the two hands are opposite in the directionality by adopting movements determined by biomechanical constraints. Likewise, this comparison allowed us to determine the relative strength of these two factors during development, when a conflict between the biomechanical constraints and cultural habits appears in the completion of a graphic task. The overall results show that the directionality can be considered as the product emerging from a complex interaction between these two types of influences. The writing habit is a determining factor when the task is performed with the right hand (dominant). But the cultural and educational factors can be modulated by the biomechanical factor when the subject uses the left hand (no dominant). This interaction varies by age of the subject.