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Change blindness

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If something in your visual field changed dramatically right before your eyes, you would notice it immediately, right? While you might think that you see or are aware of all the changes that happen in your immediate environment, there is simply too much information for your brain to fully process.

Your brain cannot be aware of every single thing that happens in the world around you. Big shifts can happen in your visual field and you are never even aware of these changes. Psychologists use the term change blindness to describe the tendency people have to miss changes in their immediate visual environment.

Here's why change blindness happens as well as the effect it can have on how you perceive and interact with the world around you.

Definition

According to a 2005 study published in the journal Trends in Cognitive Science, the term change blindness "refers to the surprising difficulty observers have in noticing large changes to visual scenes."

Why did the researchers describe the phenomenon as surprising? In many cases, the changes in the visual field are so dramatic that they seem impossible to miss. Yet when attention is directed elsewhere, people are capable of missing both minor and major changes that take place right in front of them.

"Change blindness is a failure to detect that an object has moved or disappeared and is the opposite of change detection. The phenomenon of change blindness can be demonstrated even when the change in question is large [...]"

— Michael Eysenck and Mark Keane, "Cognitive Psychology: A Student's Handbook" (2006)

Research

Perhaps the easiest way to see change blindness in action is to look at some of the fascinating experiments that have explored this phenomenon.

Blackmore, Belstaff, Nelson, and Troscianko (1995)

Participants were shown an image that was changed during a brief blank interval in the visual scene. The researchers found that the participants found it more difficult to detect changes when there was a brief break in the visual scene.

Simons and Levin (1998)

For this study, the researchers simply engaged participants in a conversation. Then, during a period of distraction, the researchers switched out the original person to someone else. Only about half of the participants noticed the swap.

O'Regan, Rensink, & Clarke (1999)

Researchers found that when small shapes are splattered over an image, such as mud splashes over a car windshield, large changes can be made to a visual scene without the observer noticing.

Previous research had demonstrated that change blindness could be produced by a visual disruption, such as flickering, blinking, or eye movement. However, the 1999 study demonstrated that change blindness can also occur without visual masking.

Levin, Momen, Drivdahl, & Simons (2000)

Researchers told observers about changes that happened in a film sequence and showed them stills from the film. 83% of the participants predicted that they would notice these changes.

However, in the original change blindness experiments that used the film, only 11% of people noticed the changes.

Feil & Mestre (2010)

Recent research also suggests that subject-matter experts may be more adept at noticing a change in their area of expertise compared to novices. For example, a physicist would be better able to detect changes to a physics problem than a college student taking their first physics course.

Causes

The ability to detect change around us plays a major role in our daily life, such as noticing when a car drifts into our lane of traffic or observing a person entering a room.

If the ability to perceive a change in our environment is so important, then why do we often fail to notice major changes?

Focused Attention and Limited Resources

At this very moment, your attention is focused on the words you are reading. While you are looking at this sentence, are you giving any attention to the color of the wall of the room you are in? Are you aware of the position that your feet are in? Until you were asked that question, it's highly unlikely that you were paying attention to either of those things.

According to researchers Daniel Simons and Daniel Levin, our attention is limited. We have to pick and choose what we focus on.

We can only focus on a limited number of objects at any given time, and it's those few objects that we pay attention to in great detail. Large volumes of information simply pass by our awareness because we lack the resources to attend to it.

Expectations and Past Experiences

Oftentimes, our expectations for what should happen in the environment can play a role in what we notice about the world.

"One reason people think they would see the changes may be that they know from past experiences that changes that occur in real life are usually easy to see. But there is an important difference between changes that occur in real life and those that occur in change detection experiments. Changes that occur in real life are often accompanied by a motion, which provides a clue that indicates a change is occurring."

— E. Bruce Goldstein, "Sensation and Perception" (2017)

We don't notice certain changes—particularly those that are artificially produced in an experimental lab—because we simply don't expect that such changes could, or would, occur.

How often in real life does a person suddenly turn into someone else, an object suddenly blink into existence, or a person's shirt change color right before our eyes?

These things simply don't happen in our day to day existence, so we tend not to notice them when they happen in a staged experiment or scene.

Other Factors

There are other factors that could influence change blindness, including attention, age, how objects are presented, and the use of psychoactive drugs. Researchers have also found that shifting a person's attention, such as by causing a distraction, leads to increased change blindness.

A person's age might also play a role: studies have found that older people are less likely to detect changes in a visual scene. Our ability to take in visual information is constrained by limited resources.

"The basic problem is that far more information lands on your eyes than you can possibly analyze and still end up with a reasonable sized brain"

—Jeremy Wolfe, Harvard Medical School (The New York Times, April 2008)

To cope with an overwhelming amount of data, huge amounts of information enter our visual system without being assimilated. Focused attention on a single part of our environment allows us to "shine a spotlight" on something that we deem to be important. We have then identified it as being something that we need to process and attend to.

Change Blindness in the Real World

Detecting change plays a major role in our ability to function in our daily life. Change blindness might cause problems in real-world situations, such as:

Air Traffic Control. Disasters and even fatalities could result if an air traffic controller failed to detect changes when monitoring take-offs, landings, and flight paths.
Driving. Failure to detect changes in the environment while you are driving can lead to dire, even fatal, consequences. Researchers have found that distractions like talking on the phone or texting while you drive can impact attention and lead to increased change blindness.
Eyewitness Testimony. Researchers have found that change blindness can affect an eyewitness's ability to recount the details of a crime or to correctly identify the perpetrator.
Social Interactions. Change blindness can affect our day-to-day social interactions. For example, making a relatively minor slip-up like asking the wrong waiter for the check when you're dining out.