Memory indexing of sequential symptom processing in diagnostic reasoning

•We employed eye tracking for process tracing of memory-based reasoning.•Gaze allocation on emptied information displays reflected information integration.•Biased symptom interpretation caused a primacy order effect.•Gaze data after the first symptom predicted final diagnoses in ambiguous items.•Spontaneously reestablished spatial indices situated cognition even after one week.

In diagnostic reasoning, knowledge about symptoms and their likely causes is retrieved to generate and update diagnostic hypotheses in memory. By letting participants learn about causes and symptoms in a spatial array, we could apply eye tracking during diagnostic reasoning to trace the activation level of hypotheses across a sequence of symptoms and to evaluate process models of diagnostic reasoning directly. Gaze allocation on former locations of symptom classes and possible causes reflected the diagnostic value of initial symptoms, the set of contending hypotheses, consistency checking, biased symptom processing in favor of the leading hypothesis, symptom rehearsal, and hypothesis change. Gaze behavior mapped the reasoning process and was not dominated by auditorily presented symptoms. Thus, memory indexing proved applicable for studying reasoning tasks involving linguistic input. Looking at nothing revealed memory activation because of a close link between conceptual and motor representations and was stable even after one week.