Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

How do people find objects in cluttered visual scenes? Think, for example, of looking for keys on a messy desk, finding the ripest-looking fruit at the grocery store, locating your car when you can’t quite remember where you parked it, or finding an old friend at an airport exit gate. Clearly, an understanding of visual perception is going to play a role in any answers, and more specifically, an understanding of visual attention will be crucial.

Visual attention refers to the ability to focus in on just part of an image, mustering one’s processing resources selectively to determine whether the thing being looked for—the target, in the standard experimental jargon—is present. To study search and attention, experimental psychologists have developed a widely used paradigm known (unsurprisingly) as visual search.

Psychologists have also motivated a great deal of research by the intuition that any good theory of search is going to have, to explain why some things are easy to find and others are hard to find. So in the context of the visual search paradigm, perceptual psychologists have often focused on contrasting easy searches with more difficult ones. The most influential contrast is between what researchers call a feature search and a conjunction search.