Under tachistoscopic viewing conditions, precuing the location of potential lung tumor targets in chest X-ray images was less effective than precuing followed by bounding the region of interest (ROI) with a circle directly on the image. Detection performance increased as the image was systematically masked so that its size approximated that of the circled ROt When viewing time was extended to allow shifts in eye position, circling the ROI was found to restrict the dispersion of fixations and increase the accuracy of fixating the target tumor. When targets were placed outside the ROI, the circle inhibited their detection relative to detection of targets inside the circled region. These findings suggest that cuing by circling restricts target detection to the ROI, and by doing so reduces the interfering effects of outside distractors that compete with the target for attention.In medical X-ray imaging, tumors of the lungs, breasts, and other major organs make up a major class of search and detection targets. The detection and recognition of these targets is especially difficult because of (1) the presence of numerous anatomical objects that also possess similar features (e.g., blood vessels on end in the lungs); and (2) camouflaging effects created by projection X-ray imaging techniques. Essentially, the observer is searching a two-dimensional, translucent picture of internal human anatomy created from the shadows of the absorption pattern of X-rays passing through the body to the film plate, and interpreting these patterns as three-dimensional objects. The magnitude of the difficulty of this particular search and detection task is evident when error rates in radiology are considered. Misses (false-negatives) of tumors, fractures, and other diagnostic findings can be as high as 30%, and false-positive rates typically run at 10%-15%