Models of expertise differences in radiology often do not take into account visual differences between diseases. This study investigates the bottom-up effects of three types of images on viewing patterns of students, residents and radiologists: focal diseases (localized abnormality), diffuse diseases (distributed abnormality) and images showing no abnormalities (normal). Participants inspected conventional chest radiographs while their eye movements were recorded. Regardless of expertise, in focal diseases, participants fixated relatively long at specific locations, whereas in diffuse diseases, fixations were more dispersed and shorter. Moreover, for students, dispersion of fixations was higher on diffuse compared with normal images, whereas for residents and radiologists, dispersion was highest on normal images. Despite this difference, students showed relatively high performance on normal images but low performance on focal and diffuse images. Viewing patterns were strongly influenced by bottom-up stimulus effects. Although viewing behavior of students was similar to that of radiologists, they lack knowledge that helps them diagnose the disease correctly.