Searching for lung nodules. The guidance of visual scanning

Four subjects searched a chest image for lung nodules using an eye position-dependent display that presented the image of a nodule selectively to either the central or peripheral visual field, while preserving the appearance of the chest. The time required to scan the image and fixate the nodule was shortest for nodules that were both reported and accessible to the peripheral vision. A stepwise concentric reduction in the size of the peripheral field that could access the nodules only affected search performance when the field was less than 5 degrees. (A chest image subtends about 25 degrees.) These data support the hypothesis that the optimal scanning strategy for lung nodules consists of spacing fixation clusters 5 degrees apart, and that peripheral vision only acts as an adjunct in guiding the gaze to inconspicuous nodules.