The paper presents theoretical propositions for modeling the expert radiologist. The propositions are twofold. First, a basic model is given to complement a recent connectionist symbolic framework (Raufaste, Eyrolle, & Marine, 1998). Empirical data have showed dissociation between two kinds of experts ("basic" and "super") with regard to cognitive flexibility. The difference is conceived as a kind of perseveration in basic experts. Hence, the basic model was combined with a Supervisory Attentional System (Norman & Shallice, 1986) into an "extended model". An analysis of cognitive activity is then presented within this framework, along with a new theoretical explanation of cognitive flexibility.