International audience This paper describes a research that has been conducted in the field of cognitive assistance to human-machine interaction in virtual environments. The idea is to design a system which, bearing in mind the actions performed by the operator at present and the current state of the environment, attempts to determine the global operation that the user is in the process of executing, and eventually takes control of the same process in order to complete it automatically. This idea implies the conception of an action recognition mechanism based on a specific knowledge representation model. This mechanism is implemented in a computer demonstrator, known as the TOAS t system, which is also presented.