Change blindness

Change blindness

In visual perception, change blindness is a normal phenomenon of the brain which show in light that the brain does not have a precise representation of the world but a lacunar one, made of partial details. Despite the name, this phenomenon does not affect the eyes but the brain, and as such is bound to happen to all the human senses. This phenomenon is still in research, but results suggests that the brain estimates the importance and usefulness of informations prior to deciding to store them or not. Another issue is that the brain cannot see a change happening to an element that it has not yet stored.

A spectacular showcase can be seen in Derren Brown's "Person Swap" sketch.


Early research

The first explorations of change blindness appear to have been conducted by George McConkie and his colleagues in the late 1970s, and focused on changes made to words and text during saccadic eye movements. A student of McConkie's, John Grimes, extended this phenomenon to the domain of scene perception (in a conference presentation in 1992, later published in a book chapter in 1996). Grimes showed that subjects would miss large changes to film scenes when the changes were introduced during an eye movement. For example, many subjects failed to notice when two people in a scene exchanged heads. In these saccade-contingent change blindness studies, changes to the scene were synchronized with measured movements of the observer's eyes, so that the changes occurred only when the eyes were moving. Under these conditions, changes are often hard to detect. (For more recent studies of saccade-contingent change blindness, see Henderson & Hollingworth, 1999, and McConkie & Currie, 1996.)

Beginning in the late 1980s, research began to reveal that other forms of visual disruption besides eye movements could also induce relatively poor change detection. Pashler (1988) showed that observers were quite 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 better change detection). He concluded by noting that people 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 sense of introspection, it seemed surprising that people's ability to detect changes proved to be so poor.

Other studies showed that change detection is also poor when the change is introduced during a cut or pan in a motion picture, even when the change is to the central actor in a scene (Levin & Simons, 1997). People also regularly fail to notice editing errors in commercial movies, despite the intense scrutiny given to movies during the post-production process.

Even information as critical as memory for the face of the person that a subject is actively talking to has been shown to be susceptible to change blindness. In a study by Simons and Levin (1998), a study confederate would stop passers-by on a college campus to ask them for directions, only to be replaced suddenly by a different confederate when a visual obstacle (two men carrying a large board) passed between them. While the two confederates presented looked different, a large number of people faced with this change failed to detect it. Change blindness has now been shown to occur with a wide variety of visual disruptions (e.g., blinks, transient noise flashed on a display, etc.).

In 1979, Neisser and his colleagues did a change blindness experiment called the ‘basket-ball game’ task which was made to seem like a visual illusion. In it, an unexpected event occurred, but the majority of observers did not report seeing it even though it is clearly visible to observers who were not engaged in the concurrent task. This is where Neisser noticed selective attention come into play. For the ‘basket-ball-game’ observers attend to one team of players, pressing a key whenever one of them makes a pass, while ignoring the actions of the other team.After about 30 seconds, a woman carrying an open umbrella walks across the screen (this video was also superimposed on the others so all three events were partially transparent. She is visible for approximately 4 seconds before walking off the far end of the screen. The game then continue for another 25 seconds before the tape is stopped (Simons and Chabris).

There is an association between Change blindness and the Mid-level vision crisis. Where there is an entire body of knowledge, still unknown, about the visual processing. Over many decades it has been disputed what lies with this change “gap’. Some theorist had found that change blindness might be a mid-level stage of visual processing. It assist in the understanding of a gap between the process of information between the lower level, which is the level that responses to visual change, and the mid-level of visual processing. Jenkin, Michael Richard MacLean, Vision and Attention 

Recent research by Ronald A. Rensink explores the question of what senses pick up. He conducted an experiment wherein observers recorded their responses on the presence of color and location,. However, he focused on what the observers "sensed" rather than what they saw. There were two experiments, the first having to do with the gradual transition of gray slides in-between the images. The second experiment had to with bright exuberant yellow slides in between. The differences in the slides had produced different reaction times and a slight discrepancy in the results. The first experiment exhibited a correspondence with sensory and seeing, finding that if the observers demonstrated a higher sense of seeing before sensing it would declare that “sensitivity of sensing does not decline with time”. The reaction time, in this experiment, is a key variable into the premise of this experiment. It can be found that with the observers, there was a variation in those who sensed a change and those who saw the change occur. The sense that something is occurring, was a common practice, it gave an air of familiarity that the observers found to have significance.[1]

In the same instance there were many false alarms being that the subjects knew something was coming about. The reaction times in different groups of observers differed from those who were highly prone to visual stimulants, such as color and those who were highly susceptible to sensation. The results of the study concluded that 30% of the observers sensed some form of change when there was a difference in images. The conscious mind was aware of the change, yet there was no visual representation of said change. In the article they call this experience one of "mindsight," defined as a “conscious experience without an accompanying visual experience” Rensink also discussed the idea that visual perception did not have to do with the observer but more with the environment in which the topic was being observed. Suggesting that change blindness is not a “weakened” form of sight but a distinctive way of perceiving images. It is not about the material it is about the individual.

Causes and relationship to other phenomena

Change blindness may be related to other induced failures of awareness, such as inattentional blindness. A crucial difference is that successful change detection in the presence of a visual disruption requires a comparison of one image to another one held in memory. Consequently, change blindness can occur due to a failure to store the information in the first place or to a failure to compare the relevant information from the current scene to the representation (hence models of visual short term memory may be important for understanding the phenomenon). In contrast, inattentional blindness reflects the failure to detect an unexpected stimulus that is fully visible in a single display—it does not require a comparison to memory.

It has been shown that change blindness can even occur immediately after an observer has identified all of the objects in a display. Becker and Pashler (2002) had observers name the highest digit in an array of digits exposed for 2 seconds, at which time the display flickered off and on (with one of the digits changed). Even though observers were almost perfect at naming the highest digit in the initial display, they were still performing at the usual, relatively low, level in spotting the change. When the highest digit itself changed, though, this change was almost always noticed.

In lucid dreaming, the dreamer notices that they are asleep and dreaming. It was thought that an ability to have lucid dreams often (more than once a month) would indicate a subject's ability to be more aware of changes in their environment.However,a study done at Swansea University has shown that individuals that have lucid dreams are as susceptible to change blindness as the general population. (Blagrove & Wilkinson)

Recent studies shown that younger adults are surprisingly poor at detecting substantial changes to visual scenes. This age difference was beyond what would be expected given known age-related changes in processing speed. Examination of eye movement behavior during the search for change suggested that age-related changes in the useful field of view and degree of cautiousness play a significant role. Speed of processing and 3 age-related eye movement behaviors explained 85% of the variance in change detection latency, eliminating the effect of age (Veiel, Storandt, Abrams).

In individuals with autism

It has been suggested that individuals with autism have atypical attentional control, possibly leading them to be unable to filter out extraneous stimuli, which would make them less prone to change blindness. In a recent study, when shown a short film with inconsistencies the autistic children were more likely to notice inconsistencies than typically developing children. (Smith & Milne)

See also


Further reading

External links

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