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.
History
Early anecdotal observations
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 earlier, William James was the first to mention the lack of ability to detect change in his book Principles of Psychology.Earliest experimental reports
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. George 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. 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. 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", and that given this introspective sense, it seemed quite surprising how poor is their detection of changes.
Research in the 1990s and 2000s
With the rise of the ability to present complex, real-world images on a computer screen, McConkie, in the early 1990s, as part of new research at the new Beckman Institute for Advanced Science and Technology, renewed investigations of why the world looks stable and continuous despite the shifting retinal input signal that accompanied each saccade. This research began when John Grimes and Dr. George McConkie began to use actual photographs to study visual stability. This development in change blindness research was able to show the effects of change blindness in more realistic settings. Additionally, further research stated that rather large changes will not be detected when they occur during saccadic movements of the eye. In the first experiment of this kind, in 1995, Blackmore et al. forced saccades by moving the image and making a change in the scene at the same time. Observers' ability to detect the changes fell to chance. The effect was stronger using this method than when using brief grey flashes between images, although subsequent research has mostly used grey flashes or masking stimuli. Another finding based on similar studies stated that a change was easily picked up on by participants when the eye was fixated on the point of change. Therefore, the eye must be directly fixated on the area of change for it to be noticed. This was called the saccade target theory of transsaccadic memory of visual stability. However, other research in the mid-1990s has indicated that individuals still have difficulty detecting change even when they are directly fixated on a particular scene. Rensink, O'Regan, and Clarke presented a picture, followed by a blank, masking screen, followed by the initial picture with a change. The masking screen acts like a saccadic eye movement. This was a critical contribution to change blindness research because it demonstrated that a change can remain unnoticed with the smallest disruptions.Research on change blindness proceeded one step further into practical applications of this phenomenon. For example, there does not have to be a masking stimulus in order for individuals to miss a change in a scene. Individuals often take significantly longer to notice certain changes if there are a few small, high contrast shapes that are temporarily splattered over a picture. This method for testing change blindness is called "mudsplashes". This method is particularly relevant to individuals driving in a car when there is a visual obstruction on the windshield. This obstruction may impair an individual's ability to detect a change in their environment which could result in severe negative consequences while driving.
Current research (2010–present)
Change detection
Research indicates that detecting changes in a change blindness task is easier when items are holistically processed, such as faces. Individuals notice a change faster when required to detect changes in facial features than when required to detect changes in images of houses. However, individuals are better at identifying the nature of the change in houses.Other researchers have discovered that mental processing in change blindness begins even before the change is presented. More specifically, there is increased brain activity in the parietal-occipital and occipital regions prior to the emergence of a change in a change blindness task.
Researchers have also indicated there is a difference in brain activity between detecting a change and identifying change in an image. Detecting a change is associated with a higher ERP whereas identifying change is associated with an increased ERP before and after the change was presented.
Additional research using fluctuations in ERPs has observed that changes in pictures are represented in the brain, even without the perceiver's conscious awareness of the change.
Change blindness can be effectively used in the process of visualizing actual changes detected in 3D scenes. With appropriate techniques it is possible to enhance the perception of the portion of a 3D scene that is changed while hiding non significant, but otherwise still visible, changes.