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A half-second glimpse often lets radiologists identify breast cancer cases even when viewing the mammogram of the opposite breast

Significance Discovering characteristics of a signal that indicates to medical experts the presence of cancer in a noninvasive screening technique in a blink of an eye has implications for improving cancer detection. Here we report two surprising facts about this signal. First, it is much stronger in the high spatial frequencies (fine detail) than in the low frequencies. Second, it is widely distributed, with signal being present well away from the actual visible locus of disease even in the breast contralateral to visible signs of disease. Although this signal is not, in itself, definitive, it has the potential to be used in automated aids to medical screening and incorporated into training protocols for medical experts, speeding up and improving cancer detection. Humans are very adept at extracting the “gist” of a scene in a fraction of a second. We have found that radiologists can discriminate normal from abnormal mammograms at above-chance levels after a half-second viewing (d′ ∼ 1) but are at chance in localizing the abnormality. This pattern of results suggests that they are detecting a global signal of abnormality. What are the stimulus properties that might support this ability? We investigated the nature of the gist signal in four experiments by asking radiologists to make detection and localization responses about briefly presented mammograms in which the spatial frequency, symmetry, and/or size of the images was manipulated. We show that the signal is stronger in the higher spatial frequencies. Performance does not depend on detection of breaks in the normal symmetry of left and right breasts. Moreover, above-chance classification is possible using images from the normal breast of a patient with overt signs of cancer only in the other breast. Some signal is present in the portions of the parenchyma (breast tissue) that do not contain a lesion or that are in the contralateral breast. This signal does not appear to be a simple assessment of breast density but rather the detection of the abnormal gist may be based on a widely distributed image statistic, learned by experts. The finding that a global signal, related to disease, can be detected in parenchyma that does not contain a lesion has implications for improving breast cancer detection.