Expertise under the microscope: processing histopathological slides Thomas Jaarsma, 1 Halszka Jarodzka, 1 Marius Nap, 2 Jeroen J G van Merrienboer 1,3 & Henny P A Boshuizen 1 OBJECTIVES Although the obvious goal of training in clinical pathology is to bring forth capable diagnosticians, developmental stages and their characteristics are unknown. This study therefore aims to find expertise-related differences in the processing of histopatholog- ical slides using a combination of eye tracking data and verbal data. METHODS Participants in this study were 13 clinical pathologists (experts), 12 pathology residents (intermediates) and 13 medical stu- dents (novices). They diagnosed 10 micro- scopic images of colon tissue for 2 seconds. Eye movements, the given diagnoses, and the vocabulary used in post hoc verbal explanations were registered. Eye movements were analysed according to changes over trial time and the processing of diagnostically relevant areas. The content analysis of verbal data was based on a categorisation system developed from the literature. RESULTS Although experts and intermediates showed equal levels of diagnostic accuracy, their visual and cognitive processing differed. Whereas experts relied on their first findings and checked the image further for other abnormalities, intermediates tended to dou- ble-check their first findings. In their explana- tions, experts focused on the typicality of the tissue, whereas intermediates mainly men- tioned many specific pathologies. Novices looked less often at the relevant areas and were incomplete, incorrect and inconclusive in their explanations. Their diagnostic accu- racy was correspondingly poor. CONCLUSIONS This study indicates that in the case of intermediates and experts, differ- ent visual and cognitive strategies can result in equal levels of diagnostic accuracy. Lessons for training underline the relevance of the distinc- tion between normal and abnormal tissue for novices, especially when the mental rotation of 2-D images is required. Intermediates need to be trained to see deviations in abnormali- ties. Feedback and an educational design that is specific to these developmental stages might improve training. Medical Education 2014: 48: 292–300 doi:10.1111/medu.12385 Discuss ideas arising from the article at ‘www.mededuc.com discuss’ 1 Centre for Learning Sciences and Technologies (CELSTEC), Open Universiteit in The Netherlands, Heerlen, The Netherlands 2 Department of Pathology, Atrium Medical Centre, Heerlen, The Netherlands 3 Department of Educational Development and Research, Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, The Netherlands Correspondence: Thomas Jaarsma, Centre for Learning Sciences and Technologies (CELSTEC), Open University of The Netherlands, PO Box 2960, 6401 DL Heerlen, The Netherlands. Tel: 00 31 45 576 2493; E-mail: thomas.jaarsma@ou.nl 292 ª 2014 John Wiley & Sons Ltd. MEDICAL EDUCATION 2014; 48: 292–300 clinical reasoning