Confidence in incomplete visual search

Visual search is critical in many activities. Under time pressure or when targets are hard to detect, decisions about target presence might be forced with insufficient information. Then an estimation of confidence is essential for subsequent actions. We asked participants to search for a small target in two search stimuli and to choose the one they felt more confident about. Target presence and the size of one stimulus was varied. The hit rate decreased as gaze-target distance increased. At large distances, hits and false alarms were similar and correlated across participants, suggesting lucky guesses. Performance was better in chosen than in non-chosen stimuli, mainly because of higher hit rate. Confidence choices preferred smaller stimuli and target-present responses. The latter preference decreased with increasing gaze-target distance, indicating reliance on target visibility. These results indicate that confidence in visual search is influenced by target visibility and the probability that the target was overlooked.