Satisfaction of search: evidence of premature termination in a naturalistic image inspection task

In radiology and in traditional visual search tasks, the detection of a first target in an image tends to impair the detection of additional targets, a phenomenon termed satisfaction of search (SOS) or subsequent search misses. The original explanation for SOS focused on early termination of inspection after having found a first target. Tests of this hypothesis have yielded mixed results, however. Here, we developed a novel task to examine the potential role of early termination in SOS. In our "Ghosts in the Forest" task, the visual search backgrounds were contour-dense natural scene images, and targets were semi-transparent face images drawn from two emotion categories: happy and angry. Targets were either high salience (HS) or low salience (LS), and scenes contained either one HS target, one LS target, or both an HS target and an LS target. First, we observed a robust SOS effect for the detection of LS targets, both in a sample of naïve observers (Experiment 1) and in a sample of radiologists (Experiment 2). Second, we observed an early termination effect following HS target detection. Third, the time spent searching after detecting an HS target reliably predicted the magnitude of the SOS effect at an individual participant level: SOS was most pronounced for those participants who terminated search earlier. Together, the results indicate that early termination of image inspection is a substantial cause of SOS in a task that embodies some of the core properties of medical image analysis.