How Change Blindness Works - Simple tests show that humans (yes, even you) tend to be clueless about very large changes - Try the test

by | Dec 14, 2009 08:00 AM ET

This video allows you to test yourself for change blindness. Watch the video before reading the rest of the post:

You might have been surprised that you missed the changes, but it is completely normal for humans. The following video presents a fascinating experiment to demonstrate how strong change blindness can be. People come up to a counter to get a form. But in the middle of the transaction, the person behind the counter is swapped for a completely different person. The new person has different face, different hair, different voice, even a different color shirt. In 75% of the cases, the people coming up to the counter don't even notice the change:

Change Blindness; you cannot be aware of everything

In the video, a researcher defines change blindness in this way:

Change Blindness is the idea that we often miss large changes to our visual world from one view to the next. We are often not able to see large changes that would appear to be perfectly obvious to someone who know they are going to happen... What's really interesting is that some people notice these changes and other people don't notice these changes, and we really don't yet have a good idea of what separates those that don't from those people who do. It might be that there are individual differences and some people are better able to detect these sorts of changes, but it is also possible that it's just coincidence that the people who noticed it just happened to be focusing on a feature that changed, that they just happened to be paying attention to the color of the person's shirt, and the people who failed to notice it just happened to be paying attention to something else.

If people can miss something as obvious as what happens in the previous video, it would seem like there is a major problem. The problem seems to be that we can only focus on one thing at a time in the visual stream, to the exclusion of almost everything else. But in the video they put it more politely: "The brain's attention system allows us actively to select what to look at. It makes us very good at concentrating on tasks, but it can also make us miss something that is happening right in front of our eyes."

You might think it is impossible for that much change to happen without people noticing it. In this video the same thing happens on the street:

Derren Brown - Person Swap

Here is another simple test of change blindness. It shows that we completely ignore the small stuff:

Change blindness

This article points out why the small stuff can change without notice: "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)."

It makes you wonder how much we miss on a regular basis. It also helps to understand why, more and more, eyewitness testimony is losing credibility:

The Problem with Eyewitness Testimony.

The article points out several things that affect the memory of an eye-witness - e.g. a process called gap-filling:

psychologists have long recognized that gap filling and reliance on assumptions are necessary to function in our society. For example, if we did not assume that mail will be delivered, or that the supermarkets will continue to stock bread, we would behave quite differently than we do. We are constantly filling in the gaps in our recollection and interpreting things we hear. For instance, while on the subway we might hear garbled words like "next," "transfer," and "train." Building on our assumptions and knowledge, we may put together the actual statement: "Next stop 53rd Street, transfer available to the E train." Indeed, we may even remember having heard the full statement.

Bias, memory distortion and false facts are also discussed.

Now that you know all about change blindness, watch the initial video again. Even though you are aware of what is happening, you may find that it is exhausting to watch the video, and impossible to see all the changes. This helps to explain why humans behave in the way that they do.

See also: How Perceptual Blindness Works – Humans (even you) sometimes completely miss things that are in plain sight – Try the test

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