Change blindness

Change blindness is a perceptual phenomenon that occurs when a change in a visual stimulus is introduced and the observer does not notice it. For example, observers often fail to notice major differences introduced into an image while it flickers off and on again. People's poor ability to detect changes has been argued to reflect fundamental limitations of human attention. Change blindness has become a highly researched topic and some have argued that it may have important practical implications in areas such as eyewitness testimony and distractions while driving.

Outside of the domain of psychology, phenomena related to change blindness have been discussed since the 19th century. When film editing was introduced in movies, editors began to notice that changes to the background were not noticed by those watching the film. Going back much earlier, William James (1842–1910) was the first to mention the lack of ability to detect change in his book Principles of Psychology (1890).

Research on change blindness developed from investigation in other phenomena such as eye movements and working memory. Although individuals have a very good memory as to whether or not they have seen an image, they are generally poor at recalling the smaller details in that image. When we are visually stimulated with a complex picture, it is more likely that individuals retain only a gist of an image and not the image in its entirety.

The laboratory study of change blindness began in the 1970s within the context of eye movement research. McConkie conducted the first studies on change blindness involving changes in words and texts; in these studies, the changes were introduced while the observer performed a saccadic eye movement. Observers often failed to notice these changes.

In the late 1980s, the first clear experimental demonstration was published showing very poor change detection in complex displays over brief intervals without eye movements being involved. Pashler (1988) showed that observers were poor at detecting changes introduced into arrays of letters while the display was flickered off and on, even if the offset was as brief as 67 milliseconds (although offsets briefer than that produced much more effective change detection). Pashler concluded by noting how odd it was that people generally report having a "clear sense of apprehending the identities and locations of large numbers of objects in a scene" (p. 377), and that given this introspective sense, it seemed quite surprising how poor is their detection of changes.

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