The decision making process is central to the practice of a clinician and has traditionally been described in terms of the hypothetico-deductive model. More recently, models adapted from cognitive psychology, such as the dual process and script theories have proved useful in explaining patterns of practice not consistent with purely cognitive based practice. The purpose of this paper is to introduce the concept of mental workload as a key determinant of the type of cognitive processing used by clinicians. Published research appears to be consistent with "schemata" based cognition as the principle mode of working for those engaged in complex tasks under time pressure. Although conscious processing of factual data is also used, it may be the primary mode of cognition only in situations where time pressure is not a factor. Further research on the decision making process should be based on outcomes which are not dependent on conscious recall of past actions or events and include a measure of mental workload. This further appears to support the concept of the patient, within the clinical environment, as the most effective learning resource.