Pop-out in visual search requires practice.

It is not always easy to locate routing signs in the visually noisy environment of public buildings. Guidelines to ensure the conspicuity of an object in a complex field are not readily available. In two previous experiments, aiming to provide such guidelines for use in practice, the stimuli were simple simulations of scenes in public buildings, each containing a uniquely colored target (a routing sign) and a varying number of distractors (advertising signs). The results of these two experiments were opposite: in one experiment pop-out of the targets appeared as predicted by current theories of visual search, but in the other experiment performance significantly decreased when the number of distractors increased. Two new experiments are reported here to clarify this discrepancy. From the results it is concluded that pop-out of easy visual targets does not occur on the first few trials of a task. Subjects must have had sufficient practice for pop-out to develop. This finding implies that, contrary to what is common in experiments on visual search, short and heterogeneous series of stimuli should be used to ensure the practical relevance of the results for applications such as sign posting.