[Radiological expertise and diagnosis. I. Theoretical advances]

From the cognitive point of view, experts are characterized (1) by the ability to directly perceive large meaningful structures due to the development of numerous links within their knowledge networks, particularly between categories that, in manuals, are described as mutually exclusive (2) by the automation of diagnosis. Even in the best experts, some biases remain, mainly due to filters in facts and hypotheses selection. These filters are based upon the resemblance of the case with prior knowledge, and upon the likelihood of previous encountering similar cases. Biases are partially balanced by heuristics which are reasoning processes, valid for a majority of cases, but which induce some errors on atypical cases.