Background Diagnostic error rates for detecting small lung nodules on chest CT scans remain high at 50%, despite advances in imaging technology and radiologist training. These failure rates may stem from limitations in conscious recognition processes. However, successful visual processes may be detecting the nodule independent of the radiologist's report. Purpose To investigate visual processing in radiologists during the assessment of chest nodules to determine if radiologists have successful non-conscious processes that detect lung nodules on chest CT examinations even when not consciously recognized or considered, as evidenced by changes in how long they look (dwell time) and pupil size to missed nodules. Materials and Methods This prospective study, conducted from [8/14] to [09/23], compared 6 experienced radiologists with 6 medically naïve control participants. Participants viewed 18 chest CTs (9 abnormal with 16 nodules, 9 normal) to detect lung nodules. High-speed video eye-tracking measured gaze duration and pupil size (indicating physiological arousal) at missed nodule locations and same locations on normal CTs. The reference standard was the known presence or absence of nodules (as determined by a 4-radiologist consensus panel) in abnormal and normal CTs, respectively. Primary outcome measures were detection rates of nodules, dwell time and pupil size at nodule locations versus normal tissue. Paired t-tests were used for statistical analysis. Results Twelve participants (6 radiologists [9.3 average years of radiological experience]) 6 controls (with no radiological experience) were evaluated. Radiologists missed on average 59% of these lung nodules. For missed nodules, radiologists exhibited longer dwell times (Mean: 228 milliseconds vs 175 milliseconds, =.005) and larger pupil area (Mean: 1446 pixels vs. 1349 pixels, =.04.) than normal tissue. Control participants showed no differences in dwell time (Mean: 197 milliseconds vs 180 milliseconds, = .64) or pupil size (Mean: 1426 pixels vs. 1714 pixels, =.23) for missed nodules than normal tissue locations. Conclusion Radiologists non-conscious processes during visual assessment of a CT examination can detect lung nodules on chest CTs even when conscious recognition fails, as evidenced by increased dwell time and larger pupil size. This successful non-conscious detection is a result of general radiology training.