The purpose of this long-term international project is to examine visual search for multiple types of target, and determine how the target information is represented in order to promote efficient and successful search.
Results from this project have demonstrated a cost in performance when searching for two types of target simultaneously, relative to two independent searches, each for one target. The cost in accuracy occurs regardless of practice or frequency of targets. Eye-movement data reveal that when searching for two targets, the representations of targets required for guiding search are less well defined than in single-target search, allowing the needless fixation of distractors that are dissimilar to either target. This work is being applied to airport security search for multiple types of threat items (guns, knives, explosives) in X-ray images of baggage. Implications of the research are that screening personnel should specialise on one type of target.