| This dissertation investigates two patterns for engaging in an activity. In the routine pattern, people begin immediately with a pre-existing, reasonably effective approach and make steady progress. In the adaptive pattern, people initially delay forward progress, spending time to prepare a new approach to the activity. The ability to follow the adaptive pattern, when appropriate, is an important component of adaptive expertise. Three studies investigated the creation of external representations as an instance of the adaptive pattern.;Graduate and undergraduate students with no medical training completed a medical diagnosis task, working from a reference dataset to diagnose new patients. The graduate students, who were relative experts in complex data analysis, uniformly took the time to create external representations. The undergraduates only made representations when an experimental manipulation (a memory burden) made their default approach impractical. Once prompted to create representations, however, undergraduates continued to do so even when they no longer faced the memory burden. In general, those with well-structured representations performed diagnoses more optimally.;A follow-up study, which collected think-aloud and video data as people completed the diagnosis task, investigated the ways in which representations changed people's use of resources in the task. It found that participants did not deliberate over their choice of initial approach to the task unless their default approach was disrupted. A third study interviewed these participants about the use of the adaptive pattern in their lives. All participants could identify examples, and in general graduate and undergraduate students told similar types of stories. There were some differences, however, which might be explained by differences between graduate and undergraduate education.;These studies emphasize the role of prior experience with the adaptive pattern in setting the stage for its future use. They highlight the importance of the evaluation horizon of an activity, as people who are only evaluated over the short term are unlikely to learn to value the adaptive pattern. They also demonstrate that the application of existing knowledge to a novel situation depends on people's values, for although all of the participants were capable of creating representations, only some chose to do so. |
