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Holistic Component of Image Perception in Mammogram Interpretation: Gaze-tracking Study¹

¹ From the Department of Radiology, University of Pennsylvania Health System, 3600 Market St, Suite 370, Philadelphia, PA 19104. Received December 12, 2005; revision requested January 24, 2006; revision received March 2; accepted April 11; final version accepted June 1. Address correspondence to H.L.K. (e-mail: kundelh{at}uphs.upenn.edu).

Purpose: To test the hypothesis that rapid and accurate performance of the proficient observer in mammogram interpretation involves a shift in the mechanism of image perception from a relatively slow search-to-find mode to a relatively fast holistic mode.

Materials and Methods: This HIPAA-compliant study had institutional review board approval, and participant informed consent was obtained; patient informed consent was not required. The eye positions of three full-time mammographers, one attending radiologist, two mammography fellows, and three radiology residents were recorded during the interpretation of 20 normal and 20 subtly abnormal mammograms. The search time required to first locate a cancer, as well as the initial eye scan path, was determined and compared with diagnostic performance as measured with receiver operating characteristic (ROC) analysis.

Results: The median time for all observers to fixate a cancer, regardless of the decision outcome, was 1.13 seconds, with a range of 0.68 second to 3.06 seconds. Even though most of the lesions were fixated, recognition of them as cancerous ranged from 85% (17 of 20) to 10% (two of 20), with corresponding areas under the ROC curve of 0.87–0.40. The ROC index of detectability, d_a, was linearly related to the time to first fixate a cancer with a correlation (r²) of 0.81.

Conclusion: The rapid initial fixation of a true abnormality is evidence for a global perceptual process capable of analyzing the visual input of the entire retinal image and pinpointing the spatial location of an abnormality. It appears to be more highly developed in the most proficient observers, replacing the less efficient initial search-to-find strategies.

© RSNA, 2007