Search for multiple targets of different colours: misguided eye movements reveal a reduction of colour selectivity

Searching for two targets simultaneously is often less efficient than conducting two separate searches. Eye movements were tracked to understand the source of this dual-target cost. Findings are discussed in the context of security screening. In both single-target and dual-target search, displays contained one target at most. Stimuli were abstract shapes modeled after guns and other threat items. With these targets and distractors, color information was more helpful in guiding search than shape information. When the two targets had different colors, distractors with colors different from either target were fixated more often in dual-target search than in single-target searches. Thus a dual-target cost arose from a reduction in color selectivity, reflecting limitations in the ability to represent two target features simultaneously and use them to guide search. Because of these limitations, performance in security searches may improve if each image was searched by two screeners, each specializing in a different category of threat ite