In daily life people apprehend a world filled with numerous objects and surfaces--a world rich with detail--or do we? Perhaps no other visual phenomenon challenges people's naive visual impression of the world more than change blindness does (DiVita & Nugent, 2000). Change blindness refers to the striking phenomenon in which observers are often unable to detect major changes made to a visual scene (see Simons & Levin, 1997, for a review) while their attention is momentarily diverted elsewhere.
Change blindness has been demonstrated using several different research paradigms. These paradigms include changing objects in a visual display (a) during a blank interval between two successive presentations (Rensink, O'Regan, & Clark, 1997), (b) while the observer blinks or makes a saccade during viewing (Henderson & Hollingworth, 1999), (c) when a set of dot patterns (a "mud splash") is superimposed on the scene (O'Regan, Rensink, & Clark, 1999), (d) during a "cut" in a motion picture scene (Levin & Simons, 1997), and (e) in the course of a "real-world occlusion event" (Simons & Levin, 1998). In all these cases, participants did not perceive striking changes in objects from one view to the next.
One popular way to demonstrate the change blindness effect is to present, in succession, an image of a natural scene, followed by a blank screen, followed by a modified version of the original scene. For example, a prominent building in a photograph may change location from one view to the next, or the propellers of an airplane--the central object in the scene--may disappear. Even after repeated presentations of drastic modifications to the original scene, observers cannot detect these changes. In addition to natural and realistic scenes, studies of change blindness have used more abstract displays in which the number of objects was carefully controlled (Becker, Pashler, & Anstis, 1999; Brawn, Snowden, & Wolfe, 1999). Although it is relatively easy to detect a change made to an item when it is the only object in a display, change detection becomes progressively more difficult when display size is increased to just two, three, or four items (Wright, Green, & Baker, 1999).
The change blindness effect has also been demonstrated for changes to more directly attended objects. A study by Ballard, Hayhoe, and Pelz (1995) required observers to match a model of stacked blocks by clicking on and dragging from a stockpile of blocks depicted on a computer display. During an observer's saccade from the location of the model to the work space, where the blocks were being stacked, the experimenters changed the color of one block in the model. This change was rarely noticed, even though participants continually attended to the model as a reference for their "matching" tasks. In another example, Levin and Simons (1997) filmed simple action sequences in which an actor sitting at a table left her chair and answered a phone ringing in the next room. The actor, the only person in the film clip, was changed during the camera "cut" that took the viewer from one room to the next. The actor was clearly the center of attention of the film, yet, surprisingly, the majority of the viewing audience was unaware that a switch had been made.
An extraordinary example entails what Simons and Levin (1998) called a "real-life occlusion event." In their experiments, the participant was asked to give directions to one of the experimenters. In the middle of the ensuing conversation, two men carrying a door came between the experimenter and the participant. While the experimenter was occluded from view, a switch was made, leaving the participant to resume giving directions to a different person once the men and door had passed by. Half of the participants failed to notice this real-world switch.
The inability of observers to detect changes under a variety of conditions has led investigators to conclude that the information encoded at any one moment in the visual scene is very selective. …