Cognitive Daily

Countless change blindness studies have showed that we’re extremely bad at noticing when a scene has changed. We fail to notice objects moving, disappearing, or changing color, seemingly right before our eyes. But sometimes we do notice the change. What sorts of changes are we more likely to notice? I’ve created a simple demo that may (or may not) help answer that question.

Take a look at this movie (QuickTime required). It will show a scene for six seconds. Then it will briefly flash white, and the same scene will be shown for another six seconds. Can you spot what has changed?

I’ve put up a poll at the end of the post so we can see if this demo works (I’m not at all sure it will!). [Update: It looks like I’ve made the task too difficult. If you don’t spot the change the first time you watch, play the movie again. You can repeat until you spot the change or you get bored with the task.]

There are certain types of changes that people are more likely to spot than others. Drug users will notice changes related to their substance of choice more reliably than non-users. In 2004, a team led by Melissa Beck found that that viewers are better at spotting probable changes (a flag starting to flap in the breeze) than improbable ones (a window changing size). Now, with a new team, Beck has started to uncover how this process occurs.

The team showed volunteers pictures like the ones in the movie above (it was actually the same set of photos used in the 2004 study, but this time the researchers also tracked the viewers’ eye movements), for six seconds pre-change and six seconds post-change. They then asked what had changed in the photo (in fact most of the time nothing at all had changed!).

As in the original study, viewers were better at spotting changes that were likely to occur in the real world than at spotting improbable changes like an object changing size or color. But several twists in this study allowed Beck’s team to uncover when the discrepancy was occurring. After the viewers completed the initial change-blindness task, they were asked to recall which scenes they had seen previously. There are two possibilities for what they saw:


Everyone saw the original image, but some viewers saw the probable change, and some viewers saw the improbable change. If a viewer had seen the probable change previously, then they were tested by being shown the original version and the improbably changed version, and asked which image they had seen previously. In every case, viewers had only seen one of the two images they were shown. Here are the results:


Viewers were much more accurate at remembering which scene they had seen before compared to their accuracy detecting the change in the first place. More importantly, there was no difference in their long-term memory for probable versus improbable changes, even though they had been more accurate in detecting probable changes.

So people accurately remember the original scene, but somehow aren’t able to report the change they see. Why is that? Take a look at this graph, showing where viewers were looking after they had failed to detect a change in a scene:


Even when they hadn’t correctly spotted the change, they looked at the place where the change occurred for longer when it was a probable change compared to an improbable change. When they did spot the change, they looked at the changed area longer, too — but for both probable and improbable changes.

What does all this mean? Beck’s team argues that the bias toward spotting probable changes occurs during retrieval: even though they remember what images they’ve seen, viewers aren’t as good at accessing those memories when a change is improbable. The memory of an image, unfortunately, doesn’t do us any good if we can’t retrieve it when we need it!

Now, let’s see if my quick demonstration movie worked. I actually changed two things in the picture: the taxi moved, and the color of the woman’s jeans changed. Which changes did you spot?

If we replicated Beck’s results, more people should have seen the taxi move (probable) than the jeans changing color (improbable). If we didn’t replicate, perhaps readers can explain why in the comments.

Beck, M.R., Peterson, M.S., & Angelone, B.L. (2007). The roles of encoding, retrieval, and awareness in change detection. Memory & Cognition, 35 (4), 610-620.


  1. #1 Austin
    September 4, 2007

    I saw neither but was aware of the quadrant in which the taxi change had taken place – even after flicking back and forward between the two images I didn’t see the jeans change colour! Couls it be that focusing attention on the “perceived” location of change, without noticing the change itself, made finding the other change less likely?

  2. #2 Dave Munger
    September 4, 2007

    Okay, after 25 votes it looks like the task is too hard — only three people saw anything change. I’ve now changed the instructions to allow people to repeat the movie until they spot the change. We’ll see if this makes a difference.

  3. #3 ctenotrish, FCD
    September 4, 2007

    I saw the pants change, but not until I had watched the clip about 6 times. I had to flip back and forth several times after that to see the car . . .

  4. #4 Adam
    September 4, 2007

    When quickly flipping back and forth between the scenes, it was fairly easy to see both changes. Before, I had a general sense that something to the left changed, but that’s it. I was particularly paying attention to the woman in red, something I should have learned not to do after watching the Matrix.

  5. #5 Ben
    September 4, 2007

    I didn’t see either change, but I think it’s because the change was in the periphery of the picture. My focus was more naturally on the prominent features (the Arc, the red shirt, the yellow sign, the number of cars and people, etc.). I should have caught the taxi change, but the pants change is harder – blue to blue is not necessarily that big of a leap.

  6. #6 Bruce Stewart
    September 4, 2007

    Even after reading what you had changed, it still took me three more viewings to see the taxi move (once you told me about the colour change on the woman’s pants, that jumped into view).

    My wife is always astonished as to how I cannot see something she is pointing out. I’d have probably seen the taxi more readily if I’d seen intermediate frames rather than just the jump from one scene to the next (which is what happens to me in the real world: I’ll see something move through the motion, but look away and back again and I won’t see what’s different this time).

    A fascinating exercise; thank you for posting it.

  7. #7 Dave Munger
    September 4, 2007


    That 2/10 of a second white screen is critical in demonstrating the effect. If there was no white screen, you would have detected the changes quite quickly. Take a look at this post for a demo of how important that very short delay is.

  8. #8 George Baker
    September 4, 2007

    I saw the taxi(car) move after going back and forth (flicking) between the two. Missed the jeans completely. Great experiment though

  9. #9 Sam Wise
    September 4, 2007

    Mark me down as another taxi person. I “only” had to watch the movie twice — the first time, I thought “something” changed in that rough area of the image, but couldn’t tell what exactly had happened. The second time, I focused on where I thought the change occurred, and saw the car move.

  10. #10 oldcola
    September 4, 2007

    Hi there,
    Interesting exercice. I answered the pool as a “taxi person”, but that was at the first time. Once I knew that the taxi was one difference I tried several more time. Second one brought out the color change. Sixth convinced me that there was something else different: the “taxi” moves, I hadn’t see it hidden by the people, just noticed it was gone on first viewing. But I was sure something else was changing.
    Now, is it really a “taxi”?

    Answered “I saw the taxi” move, considering that the first impression was to be logged.

  11. #11 Jessica
    September 4, 2007

    On the first viewing, I knew something changed in the area around the taxi, but first thought it was a person who disappeared. I had to check a couple of times to catch the taxi (but wasn’t even looking at the woman in jeans, because I was paying attention to another part of the image.)

  12. #12 The Ridger
    September 4, 2007

    After I looked at the poll the jeans jumped out at me. The taxi I didn’t notice until the 12th time through and AFTER I read the comment about it being hidden by the people.


  13. #13 V
    September 4, 2007

    I saw something happen in the area where the taxi moved, but I thought it had something to do with the people. As soon as I started flipping between both pictures I saw both changes.

  14. #14 Kawe
    September 4, 2007

    I noticed the general area of the taxi moving on the first try. The pants I didn’t even try to find since I assumed there was only one change (that’s what you get for putting instructions after the movie). Not only that.. it was placed in a really bad place I think (off to the edge). But then I guess that’s an improbable place for things to change in a picture (compared to the center of a picture). However it was easy to spot after I read about it since there aren’t too many pants to keep track of.

  15. #15 Stephen Downes
    September 4, 2007

    It was too small, I couldn’t even see the taxi until I squinted right up close to the screen.

  16. #16 James Bach
    September 4, 2007

    Putting my eye in the center of the picture, I saw the jeans change right away (actually I noticed something change in the corner and played it again to see that it was jean color).

    But then I replayed a third time to see if the other people had changed color, too, and confirmed that they don’t change. Even though that is where the taxi moves, I didn’t see the taxi. I was focused on the people. I only noticed the taxi when I fast flipped between the first and second image.

  17. #17 Brane
    September 4, 2007

    I noticed the pants change the first time, but – didn’t remember the color of the jeans, just that they changed. Did also notice “something” in the area of the car, but somehow came to the conclusion that it instead was the man’s pants which also had changed.

    I have to say that I sort of expected it too be a color change somewhere, so I might be biased. I have previously noticed in “find 5 faults” type of games, that color changes are the by far the easiest for me to spot. The hardest would be minute details of an otherwise busy scene. The brain probably abstracts away the detail to present a more usable model/s to the brain, but color changes (and contrast changes, such as something appearing in an otherwise empty space), seem to register quite well.
    Haven’t ever concidered (or noticed) the “most likely event”-change to be significant, wierd changes seem to register better with me. But perhaps I’m just wierd then.

  18. #18 Susannah
    September 4, 2007

    I didn’t see the taxi move on the first go-round, but I did notice that that side of the screen “felt” emptier. I got it quickly the second time.

  19. #19 Piper Wilson
    September 4, 2007

    Once I knew to look for the taxie, I was able to figure it out. I think my “americanism” got in the way. I kept looking for a mustard yellow monstrosity thing.

    I’d’ve noticed that change colors.



  20. #20 Zs
    September 5, 2007

    For some reason I was focused first on people moving and if there are changes in the central construction.

    I noticed the jeans, but I was so focused on the arch that I did not see the taxi moving 🙂

  21. #21 Freiddie
    September 5, 2007

    I didn’t see any changes because the photo has too many things to focus on – so many cars, people, buildings etc. Unlike the diagram of a dog and a simple house, this one is too hard. I gave up and just flickered back and forth with the mouse so that the change would be more obvious and the blank part of the clip is reduced in duration.

  22. #22 lakelady
    September 5, 2007

    It took me several tries but the first change I noticed was the jeans. I actually expected the cars to change but didn’t see that until after I read the article, went back and immediately saw the taxi change. I might have seen the taxi change if I’d tried some more times, but once I saw a single change I wanted to get on with reading the article.

  23. #23 Mike
    September 5, 2007

    Obviously this example is not representative of the 10 million other scenarios that could have been used, but I wouldn’t chatecarize it as “too hard”. The reason why people — such as myself — didn’t get it is because nothing of consequence changed. The brain has enough to process without worrying about nothing.

  24. #24 Dangerous Dan
    September 5, 2007

    I played the scene several times without being able to see any change, but the first time I skipped over the white blanking interval in the middle, both changes jumped out at me.

  25. #25 James
    September 5, 2007

    I spotted both changes, but only after viewing the movie 6 or 7 times. I also noticed both changes in the final viewing. I think this has something to do with both changes occurring on roughly the same horizontal plane. I wonder if there is any indication of this in the study. Are improbable changes more likely to be noticed when they occur near probable changes?

  26. #26 Richard
    September 6, 2007

    I can’t say I saw the taxi move as much as I saw the space where somethng was where I just happened to have my eyes focused. The thing that throws you off the most is the white flash -do you have that included for a purpose other than a break between each sequence?

  27. #27 Judge
    September 6, 2007

    I didn’t see either change until I flicked between the two images, then they both jumped out. I’m not sure it’s really fair to characterize the movement of the taxi as “probable”. Cars don’t usually disappear suddenly or change position when everything else remains stationary.

  28. #28 Dave Munger
    September 6, 2007

    Obviously this example is not representative of the 10 million other scenarios that could have been used, but I wouldn’t chatecarize it as “too hard”. The reason why people — such as myself — didn’t get it is because nothing of consequence changed.

    It was “too hard” the way I originally posted it because only a miniscule fraction of viewers noticed any change. It would have been impossible to determine which change was spotted more often.

    The change blindness effect can work even when the change seems quite obvious. Clearly more obvious changes are spotted faster, but what’s interesting about this study (and confirmed by the demo) is that changes that occupy the same portion of the visual field and have the same importance in the picture are spotted at different rates. The visual system appears to be biased to notice “possible” changes, and this study has pinpointed that bias to the retrieval phase.

    We actually remember what has changed, but can’t recall it at the critical moment — and this occurs more frequently when a change is improbable.

  29. #29 Ann F
    September 6, 2007

    I saw the taxi change after five viewings. During the fourth, I became aware of that general area as being the source of the change.

    My strategy was actually to look at the people, and then the cars, as the most likely spots to change, for what that’s worth for your theory!

  30. #30 Bill
    September 6, 2007

    I was immediately aware of the general areas where there were changes but it took another viewing to identify the taxi and two more for the pants.

    My sense is that the pants is something we filter out as noise as it is the sort of change that can be just glare or exposure rather than a change to the actual object.

  31. #31 TanGeng
    September 6, 2007

    I noticed the two changes, but since I was forewarned about looking for changes, I didn’t focus on picture features and instead just looked at the picture as whole.

    It was easy to pick out the two changes. Although, the taxi movement registered as a moving car immediately, while I didn’t really understand the color change in the jeans until I looked and recognized they were jeans.

    By that time, I had forgotten what the original color was and I only know that the color had changed.

  32. #32 Mark thomas
    September 6, 2007

    Change detection may have occurred even if it wasn’t reported. Not reporting a change does not always indicate that a person did not notice the change. People sometimes look at the changed object longer than other objects in change blindness paradigms. This looking behavior has been interpreted to mean that there was a failure in retrieval or comparison between the pre and post change memory representations. One of the earlier posts noted, “Did also notice “something” in the area of the car, but somehow came to the conclusion that it instead was the man’s pants which also had changed,” and several of the posts claimed to notice the areas in which the changes occurred, but not to be able to report the change. If you don’t know something about it, how do you know to attend to the area that is changing? From Henderson, J. M., & Hollingworth, A. (2003). Global transsaccadic change blindness during scene perception. Psychological Science, 14,493-497. “Fixation duration has been shown to be a sensitive measure of covert (i.e., unreported) change detection (Hayhoe et al., 1998; Henderson & Hollingworth, 2003a; Hollingworth & Henderson, 2002; Hollingworth et al., 2001).”

  33. #33 Russ Abbott
    September 10, 2007

    I saw neither in the movie. (I watched it twice.) But then I stopped the movie and flipped manually between the two images. It was obvious then what changed.

  34. #34 The Happy Rock
    September 11, 2007

    Any thoughts of making a similar video with easier changes and retrying?

  35. #35 KayCee
    September 25, 2007

    I did not notice any change at all during the exercise. Not until after I saw the choices did I see how obvious they were after I tried again.

  36. #36 Who Cares
    November 22, 2007

    Funny. I saw the change of the jeans (at the second attempt) then kept redoing the movie because there was something else that had changed to but I couldn’t pinpoint it (4 more attempts to see the car being removed).

  37. #37 Patrik
    December 7, 2007

    I am really blind. I didn’t see anything change even though I repeated the movie like 8-10 times. Finally I switched between the two movies rapidly and then I spotted both the changes but that’s of course serious cheating 🙂

  38. #38 Linus
    July 15, 2009

    Cheat sheet!!

    When the first piece is playing, jump to the second piece – and the changes jump out at you. Loud and clear.

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