Chest "gestalt" and detectability of lung lesions

Image perception in chest radiography is thought to occur on two levels, (a) a fast global response based on learned templates ("gestalt") and, (b) a slower systematic scan process. The relative importance of "gestalt" on the detection of nodular lung cancers was studied by disturbing the "gestalt" through rotation of the radiograph but not actually diminishing the image content available for viewing. Sixty chest radiographs (20 normals, 21 with subtle lung cancers, 19 with obvious lung cancers) were presented to three readers in normal and abnormal (rotated randomly in 90 degree increments) orientation for varying durations (0.25 s, 1 s, 4 s and unlimited viewing time). The results indicate that the detectability of obvious and subtle lung lesions was degraded by the disturbed "gestalt" for both short and long viewing times. The readers did not significantly increase their unlimited viewing time when faced with rotated images (4.4 +/- 3.4 s) as opposed to non-rotated images (4.0 +/- 3.2 s). We conclude that the detection of lung lesions relies heavily on the chest "gestalt" and that systematic scanning cannot fully compensate for an impaired global response due to a disturbed "gestalt."