To make it easier to manipulate in direct action and to manage the degrees of freedom of a virtual dummy, the invention provides a graphical interface system enabling two windows to be displayed on a screen. The first window contains an overall representation of the dummy making it possible, using pointer means such as a mouse, for example, to select a member of the dummy directly on the screen. In response to such selection, the selected member appears in the second window on a larger scale together with symbols indicating all of the degrees of freedom available on the member in question. The operator can then act directly on the symbols of the degrees of freedom to block or unblock them or indeed to manipulate the dummy in direct action.