Search efficiency for multiple targets

In most visual search experiments, there is only one possible target object or class of objects. The experiment reported here compares performance in these single-target searches against performance when the target can be either of two different stimuli. The targets used in this experiment were color squares. Results showed that conducting two single-target searches is more efficient than carrying out a dual target search. If visual search is driven by a mental template of the object to be found, then searches for two targets may require a very general template, or a pair of templates that are active simultaneously, which apparently produces less efficient search. Many real world search tasks, such as searches of X-ray images by baggage screeners, require simultaneous search for very different targets (“Find any guns or knives or explosive devices.”). This need for generality could result in search that is less directed and therefore less efficient