Categories of observer error from eye tracking and AFROC data

Abstract

Twenty-four volunteer observers were divided into groups of eight radiologists, eight radiographers and eight novices to carry out a pulmonary nodule detection task on a test bank of 120 digitized PA chest radiographs. The eight radiographers were tested twice: before and after a six-month training program in interpretation of the adult chest radiograph. During each test session the observers eye movements were tracked. Data on the observers' decisions through AFROC methodology were correlated to their eye-movement and fixation patterns. False negative error-rates were recorded as 41% for the radiologists, 45% for the novices, 47% for the radiographers before training and 42% for the radiographers after training. The errors were sub-classified into search, recognition and decision errors depending on the duration of the fixation-time for each faulty response. Errors due to satisfaction of search were determined from images with multiple nodules. Differences between the groups were shown. Errors due to inefficient search were in the minority for all the observer groups and the dominant cause of unreported nodules was incorrect decision-making. True negative decisions from all observers were associated with shorter fixation times than false negative decisions. No correct negative decisions were made after fixations exceeding three seconds.