The authors present the notion of anticipation range, and emphasize the interest of this concept for studying the anticipation activity in the control of dynamic environments. A dynamic environment is characterised by a spontaneous evolution, that is to say the system changes independently of the operator's actions. Some differences between anticipation in dynamic situations versus anticipation in static ones are clarified, along with two kinds of anticipation: a sub-symbolic one and a symbolic one. The anticipation range is defined as the set of elements that are considered by the operators while anticipating the process evolution at a given time. It is presented as related to knowledge organization in memory, and to the building of functional representation. Two dimensions of the anticipation range are hypothesised: one of them is related to time and the other is related to the objects of anticipation. A verbal protocol analysis was carried out in an Air Traffic Control situation. Data were gathered during an anticipation task and processed with an automatic textual data analyser (Alceste). Alceste is based on automatic parsing, and uses a hierachical descending classification. Results showed some variability in the anticipation range according to the role played by the controllers (radar or planning controller). In particular, the objects included in the anticipation range were different. This variability involved some elements of cooperative work, and certain characteristics linked to the complexity of the problems to be processed. For instance, with a descending or climbing aircraft both controllers appeared to be more involved in a cooperative activity. We conclude from an ergonomic point of view: the obtained results are to be considered for the design of an anticipation aid for air trafic controllers. The variability of the anticipation range involves different needs according to controllers' functions.
