Change blindness is what happens when a person fails to recognize the change in an object or scene when that change coincides with a brief visual disruption (Simons & Levin, 1997).
Change blindness occurs when we don’t perceive the motion that happens when a stimulus moves from one location to another in a visual scene (McConkie & Loschky, 2006). It often happens as a result of selective attention.
Change blindness happens regularly, for example, in magicians’ tricks, where the magician will use a distraction in one hand while changing cards in the other hand, which prevents observes from observing the switch.
Change Blindness Definition and Overview
Simons and Fracnoneri (2000) define change blindness as: “a surprising inability to detect large changes to scenes from one view to the next.”
Of note in this definition is that change blindness can occur even when the stimulus that has changed is quite large. This can happen with objects presented in still images, motion pictures, and even in real-world situations involving interpersonal interactions.
In a representative study, Simons and Levin (1998) conducted an ingenious investigation of change blindness in a real-world situation.
An accomplice of the study, carrying a map, asked directions from a stranger near a university campus. While the stranger was giving directions, two other accomplices carrying a large door walked between them.
In that moment, the first experimenter was replaced with another experimenter that looked similar, but was in fact dressed differently and was in fact, a different person: “yet, despite clear differences in clothing, appearance, and voice, only 7 of the 15 pedestrians reported noticing the change of experimenters” (p. 646).
Types of Change Blindness
There are two types of change detection: via a sensory transient signal and via inference.
- Sensory transient signal change: Thisoccurs immediately as a result of one object immediately replacing another. The change is noticed as a result of visual detection produced by a transient signal. This signal happens automatically and brings the change into conscious awareness (Reichardt, 1961).
- Inference: Inferential change detection occurs after a gap in the presentation of the two stimuli and involves a more cognitive process. For example, it can take some time to notice the change in hairstyle of a coworker. The gap from one stimulus presentation (coworker on Friday) to the second presentation (coworker on Monday) produces change blindness. This type of change detection occurs as a result of comparing the current image with information stored previously in memory.
James (1950/1891) made note of this distinction between the two types of change detection over 100 years ago:
“With such direct perceptions of difference as this [sensory transient signal], we must not confound those entirely unlike cases in which we infer that two things must differ because we know enough about each of them taken by itself to warrant our classing them under distinct heads. It often happens, when the interval is long between two experiences, that our judgments are guided, not so much by a positive image or copy of the earlier one, as by our recollections of certain facts about it.”(p. 496-497, words in square brackets added)
Since those earliest days of discussion, research has found change blindness can occur during a brief flash on a computer screen (Rensink, O’Regan, & Clark, 1997; Simons, 1996), in movies (Levin & Simons, 1997), or in the blink of an eye (O’Regan, Deubel, Clark, & Rensink, 2000).
Change Blindness Examples
- In Movie Scenes: There are lots of examples in the movies of an object being misplaced or even absent from one scene to the next. Although the director did not intend those errors to be included in the final cut, sometimes they get through anyway. Audiences rarely take notice.
- In Rescue Operations: The Coast Guard sometimes has to attempt a rescue in turbulent seas. Trying to lower oneself to rescue a drowning victim requires a continuous monitoring of the victim’s location, who is being thrown about by large swells and might actually get submerged for several seconds at a time. In this kind of emergency, there is no room for change blindness.
- In Checking Programming Code: Programming languages can be quite complex and developing software can involve hundreds and thousands of lines of code, worked on continuously by a dedicated team of programmers. Being able to check those lines through multiple iterations is a painstaking task that requires a keen eye for detail. Change blindness can make that process ever more time-consuming and extremely inefficient.
- In Older Drivers: Older drivers are more likely to miss changes in their visual field compared to younger drivers. This was demonstrated in research using photos of intersections that altered images of pedestrians, vehicles, signs, or traffic control devices.
- When Spies Switch Drinks: In a lot of spy movies there is always a scene in which two enemies pretend to be having a friendly drink together. As one of them turns their back, the other puts poison in their glass. If the one getting the poisoned drink experiences change blindness, then its game over for them.
- In Eyewitness Testimony: Although most people are confident in their memory, research on eyewitness testimony says otherwise. Research has demonstrated that change blindness can occur when the perpetrator of a burglary is switched half-way through a video reenactment of a crime. Over half of viewers did not notice the change at all.
- Air Traffic Controllers: If an air traffic controller experiences change blindness, it could result in disaster. The screen they monitor contains a large number of images that are in constant motion. Failing to recognize a change on the screen is a mistake that can have deadly consequences.
- Playing Video Games: So many games involve rapidly changing images and scenes. Players have to keep their eyes focused on the screen at all times. Even a momentary lapse of attention can lead to change blindness, and then…game over.
- In Combat Situations: Operating modern military equipment involves personnel being heavily loaded with visual processing tasks, situation assessments, voice communications, and the tactile manipulation of numerous displays. Research has demonstrated that change blindness can easily occur in these highly stressful situations and lead to substantial negative consequences.
- When Conducting Research: Naturalistic observation is a type of research that involves watching and recording behavior. That could be the behavior of people or animals. The researcher has to have a trained eye for detail and needs to be able to notice very minute changes in behavior. Having a bout of change blindness can mean missing key moments and jeopardizing the study’s validity.
- Monitoring Airplane Cockpit Instrument Displays: If you have ever seen the inside of an airplane’s cockpit, you will be amazed at the dizzying number of instrument displays. A pilot has to monitor the information presented by all of those instruments and be acutely aware of any significant changes. Even a brief moment of change blindness may lead to an emergency.
Applications of Change Blindness
1. In The Movies
As Simons and Levin (1997) point out, directors and editors exert considerable effort to eliminate flaws in the continuity of scenes.
Unfortunately, because scenes are often shot out of sequence, perhaps even on different days, there are many occasions in which the objects in one scene have been moved slightly or might even be absent in the next.
Fortunately, nine times out of ten, those errors will not be noticed by the audience due to change blindness (Dmytryk, 1984).
Film makers are especially knowledgeable of how people process visual scenes. They often use that knowledge to create a sense of cohesion and continuity to a scene.
Some even employ different techniques to facilitate that perception by cleverly inserting elements that will cause the audience to blink at just the right moment. In this way, they capitalize on change blindness to construct a desired perception.
2. In Eyewitness Testimony
Our understanding of change blindness has also been applied to the accuracy of eyewitness testimony (Loftus, 2019). Research has already demonstrated that eyewitness memory is easily altered and manipulated (Loftus & Palmer, 1974).
Change blindness can also be an issue. For instance, Davies and Hine (2007) produced a short video depicting a burglary. However, half-way through the 2-minute video, the burglar was switched.
Burglar 1 was 170 cm tall, slightly built with an oval-shaped face. Burglar 2 was 188 cm tall, heavier, and had an oval-shaped face. Both burglars wore dark clothing, but according to the researchers, the style and detail differed considerably.
Afterwards, the research participants were given a questionnaire which asked “Did you notice anything change about the burglar throughout the film?”
The results showed that “only 39% of participants noticed the identity change” (p. 431). This percentage is similar to that obtained by Davis et al. (2008). Similar results were also obtained by Levin and Simons, (1997) and Levin et al. (2002).
While 95% of participants in Nelson et al. (2011) experienced change blindness while watching a simulated crime video, they also found that increased severity of the crime led to fewer errors identifying the perpetrator.
The overarching message from this line of research is that change blindness can lead to inaccuracy identifying criminals, create errors in eyewitness testimony, and may ultimately lead to wrongful convictions.
Change blindness refers to not noticing a change from one visual stimuli to the next. Some of the earliest discussions of change blindness occurred in the film industry. Film makers noted that most viewers failed to detect errors in the continuity from one scene to the next.
Although seemingly unimportant at first, researchers have since connected change blindness to a variety of consequential situations.
For instance, an eyewitness to a crime can fail to correctly distinguish between two suspects due to change blindness. Similar looking suspects are sometimes not even noticed as being two different people.
Older drivers are more likely to experience change blindness, which can mean not noticing pedestrians abruptly appearing in the street or a change in traffic signals.
Change blindness also has significant implications for professionals that operate sophisticated machinery such as airplanes or military equipment. The failure to recognize changes in instrument displays of essential data can have profoundly negative consequences.
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