Jan 21 2014

A New Wrinkle on Change Blindness

I have discussed previously the phenomenon of change blindness – look at a picture which then winks off and then back on again. In between something may have changed. Would you detect it? Psychologist have found generally that people are pretty bad at detecting such changes.

Here is a nice demonstration of this phenomenon  by my colleague, Richard Wiseman. Just search for “change blindness” on Google and you will find many more.

Interestingly, if the change occurs without the picture winking off, in other words it occurs before our eyes, we are pretty good at detecting the change. Our attention is drawn to the change. But when the change occurs outside of our vision, we are bad at detecting that a change has occurred.

A similar phenomenon is inattentional blindness. Here is the classic demonstration of this.  (If you have ever seen it, take a look before reading on.)

The lesson with both of these related phenomena is that our brains process only a subset of the sensory information that comes in, and we attend to an even smaller subset.

How much information, however, is processed subconsciously – without our conscious attention?

A new study published in PLOS One takes a peek at this question. They conducted a classic change blindness experiment, showing subject pictures that wink off and then back on, and a change may or may not have occurred between the two. Researchers Howe and Webb asked subjects if any change occurred, and what was the change.

They found that subjects in most but not all of the trials were better able to detect that a change had occurred than to be able to name the specific change. They did the trial with faces, inverted faces, and simpler stimuli (green and red rectangles). The biggest difference occurred in the latter trial:

When a change occurred, observers detected the change on approximately 88.7 trials. Of these trials, observers went on to correctly identify one of the disks that had changed on approximately 64.2 trials. This meant that approximately 24.5 of the trials were only-sense, which was significantly more than the 3.2 trials that would have been predicted by a guessing strategy, t(9) = 8.99,p<0.001, Cohen d = 4.27.

So in this trial almost a quarter of the time (there were 100 trials total) the subjects were able to state that a change occurred without being able to identify a specific change. This was true of 13 of the subjects in the face trial, and 20 in the inverted faces trial.

In the rectangle trial discussed above the proportion of red to green rectangles changed. The researchers also ran a trial where red and green rectangles were swapped but the proportion did not change. In this trial there was no significant difference in “sense only” outcomes from chance.

What does all this mean? Some of the time we are able to detect that a change has occurred even if we are not aware of what that change is. This is likely due to processing involving the whole scene, rather than paying attention to and remembering specific details.

In the fourth trial where the rectangles changed but not the proportion, subjects could not detect change unless they were also able to identify a specific rectangle that changed. This makes sense because in this simple situation, only the details changed, not any overall aspect of the picture.

With faces, however, subjects were sometimes able to know that a picture had changed even when not aware that it was the glasses that had changed. This implies that our brains get an overall impression of a face (even an inverted face) and this overall impression is influenced by the details, even when we are not consciously aware of those details.

This is in line with previous psychological studies that indicate that subjects can react to cues of which they are not aware. We may respond emotionally to a face or be biased in our reactions, even when not aware of which facial features are generating that reaction.

This all fits in generally with how we currently understand human brain function – specifically that a great deal of processing occurs at a subconscious level and we are consciously aware of the net effect without being aware of all the elements that contributed to that net effect (how we feel, or what we decide, for example).

In this study there is also the specific element of visual processing. Our ability to detect that the proportion of green and red in a picture has changed, for example, may be more due to specific visual processing than something more general about attention.


As with most similar research, the message that the general public can take away from such research is to be aware of the limitations and foibles of how our brains function. Taking in and being aware of information is a process, and that process is flawed, incomplete, and biased.

The end result is that we can never be entirely sure of what we think we remember about what we think we experienced.

Ben Radford also discussed this experiment and made an interesting observation – that such subconscious awareness might give us some insight into why some people believe they have psychic powers. He argues that people have the ability to take in a great deal of social information about people without being able to necessarily identify which details influenced their assessment.

Alleged psychics may be fooled by this process into thinking that they are getting information from a paranormal or extrasensory source, when in fact they are simply subconsciously processing visual or other sensory information.

While I think this is essentially correct, I’m not sure this study directly relates to that conclusion. This study was about change blindness, and not about the subconscious processing of social cues, but the underlying principle, that of subconscious processing, is the same.

In any case – the study does contribute to the overall psychological and neuroscientific literature which clearly adds up to the conclusion that we all need to be aware of some of the basics of how our brains work, and this should make us humble in the face of the uncertainty this implies.

23 responses so far

23 thoughts on “A New Wrinkle on Change Blindness”

  1. SteveA says:

    The Wiseman video is incredible. Fooled me on all counts.

  2. CW says:

    I have seen that Wiseman video several times and I always forget about the tablecloth.

  3. Kawarthajon says:

    There was a great article in either Scientific American or Scientific American Mind a couple of months ago that went into detail about how poor a picture our eyes actually take of the world. It also talked about how there are significant blind spots in our eyes that impact what our eyes can see. What we experience, however, is something completely different – we see a smooth, clear picture because our brain does so much processing and fills in the blind spots so we don’t ever notice they’re there. It was especially surprising when the article pointed out how to find your blind spots and I became aware of them. The Wiseman video had the same effect on me.

  4. nybgrus says:

    There was a good TED talk on this sort of topic. The guy was showing how we need processing power to actually notice changes and that he can sap away our ability to pay attention. Very cool video. The major changes are blink changes but there are subtler ones that happen right in front of you that you’ll miss. I found it worth watching.


  5. Andrew Cooper says:

    It’s an excellent video: required viewing for all school students at some point in their education. And everyone else, of course.

    On a related point, if anyone is interested in learning about psychology – specifically social psychology – I would strongly recommend this Coursera course https://www.coursera.org/course/socialpsychology The course references the Wiseman video during its coverage of the social construction of reality. It also covers confirmation bias and much, much more.

    I took it on its first presentation last year and while I knew about some of the material it covered the presentation by Professor Scott Plous at Weslyan University is absolutely excellent and both thought provoking and highly practical. I think it would be of interest to all sceptics.

    I’ve tried a couple of Cousera courses but this has been by far the best and it’s the most popular course on Coursera in terms of enrolments.

    Hope you don’t mind the buzz marketing but the course is free to take.

  6. Sherrington says:

    I seem to recall a study from a few years back where researchers had participants look over a room and then, while they were not looking, removed an object. It was shown that even if the people could not identify the missing object, tracking of their eye movements showed that they spent a good amount of time searching in the area where the object had been. This seems to fit in with this. (I tried to track down that article, but could not find it. I even looked at the PLOS One paper to see if it was mentioned in the introduction or discussion, but could not find it). DISCLAIMER: I am repeating this study from memory and therefore this is subject to usual reconstruction of memory that occurs in these circumstances.

  7. ccbowers says:

    “The guy was showing how we need processing power to actually notice changes and that he can sap away our ability to pay attention.”

    I wonder how noticing changes correlates with variations in attention, for given person and across people. I imagine that if I have trouble concentrating on the activity, that my attention may stray towards those things that may change (like shirt color), which would otherwise be ignored as irrelevant by a person focused on the activity.

  8. Sorry, Steve but why is any of this new? For example, in most countries the coinage have distinct images on them, usually at least on one side. If a person in that country has no interest in coins they wouldn’t be able to tell you what images are on which coins even if they handled them hundreds of times a day. I’m sure if you’d pointed this out to Thales he would have yawned…

    Perhaps it’s more interesting to try to figure out why we know what we know, rather than point out the enormous and seemingly endless failings of human brains. At some point travelling down this particular rabbit hole starts becoming a waste of academic time.

  9. Andrew Cooper says:


    Steve discusses what might be new about this in his conclusion. Rather than object to the whole idea of research in this area why don’t you deal with the specific points he raised? Your surmise about coins isn’t relevant I’m afraid. Even if it was, it hardly amounts to a case against properly researched peer reviewed findings. If you’re not interested in this topic and can’t see its relevance you are probably reading the wrong blog.

  10. Bruce says:


    Perhaps you should change your name to Will Nitpicks. I do wonder why you keep stating this blog and the research it covers is a waste of time. I think it is well worth the entertainment value every day now to see what you will say in response to every blog. If nothing else, the studies are indirectly providing me with entertainment through your pokey pokey negative comments.

    And guess what, you just wasted even more time reading a response to your waste of time comment on a blog that you think is a waste of time about a study you feel is a waste of time.

  11. BillyJoe7 says:

    The biggest waste of time on this blog for a long time has been reading and responding to WN.

  12. tmac57 says:

    ntbgrus,-That TED talk was fun to watch.I only caught a small portion of his misdirections even though I was really watching for them.

    Here is a link to a site that has many examples of change detection tests:


  13. @Steve,

    I’ve taken a closer look at this study and the more I’ve read the more depressing it gets. Psychology seems to be stuck in a loop, going around in endless circles. Rather than waste more time on figuring out what people can’t do, perhaps these researchers could do something constructive, look work in vision detection research. I.e., build actual mathematical models of vision systems that could be implemented in software. If they are not smart enough to work in those areas, that’s fine. Maybe they need to review why they are doing what they are doing and opt out of the field so that very limited academic resources can be used more productively by smarter people. There is nothing in this paper I learnt that I didn’t read about 30 years ago. The conclusion didn’t even attempt to describe how what they had just done might in any way be of any actual value, theoretical or practical.

  14. shchasm says:

    Do any of these studies resemble what was presented in the videos? It seemed to me that all the videos were examples of misdirection or demonstrating that our brains aren’t really efficient at multitasking. Every video asks the viewer to focus on something (cards, a conversation, counting basketball passes, etc…) while changing generally insignificant details. It seems we would have little difficulty detecting many of these changes if we weren’t deliberately distracted, like cell phones and driving. Even the guy giving directions seems to be just merely misdirection, changing a detail he could probaly care less about because he’s focusing on a task. I’m by no means an expert in anything…Just practicing critical thinking skills.

  15. Davdoodles says:

    I’m with Will N.

    I don’t like much of anything, nothing here is interesting or new to me, and nobody is very clever.

    So, I’ll hang around this blog pointing that out, incessantly, for some reason.

    Rather than, you know, starting my own blog about things I like, which are interesting, new, and clever.

  16. SteveA says:


    I don’t think deliberate distraction is the issue. It’s not like we walk around with a 360 degree radar than only focuses on one thing when we’re asked to. We’re focused on something all the time, only taking in a fraction of the reality that surrounds us.

    My favourite example of change blindness is the white bartender who drops behind the counter to get a customer a glass and comes up as a black guy. I’ve seen it done a number of times. Hardly anyone notices. No distraction there. It’s just life.

  17. SteveA says:

    @ Will N

    We’ve had some first-class dingbats trolling on this forum over the years. Frankly, were used to better. A lot better.

    If you’re not smart enough to work in this area maybe you need to review why you’re doing what you’re doing and opt out of this field.

  18. @Steve

    Perhaps you could write an interesting blog post on why amateur skeptics resort so easily into ad hominem?

    Here is a tip. 3 quick bullet points on why this research is important/relevant or what benefits or possible benefits it might provide, would have been devastating to my case, if you could have thought of clever things to write. Your actual response makes you look like (some) of your audience of readers.

  19. rezistnzisfutl says:


    Us “amateur skeptics” aren’t resorting easily to ad hominems so much as we’re responding to you, a known troll. You’ve shown your true colors and most of us here don’t want much to do with you, and certainly don’t take you seriously. That’s why it’s easy to resort to minor ridicule in your case.

  20. Bill Openthalt says:

    Will Nitschke

    Since you’re the person who introduced the term amateur skeptics, pray do enlighten us and let us know who, in your opinion, are professional skeptics?

  21. SteveA says:

    @Will N

    “Here is a tip. 3 quick bullet points on why this research is important/relevant or what benefits or possible benefits it might provide, would have been devastating to my case, if you could have thought of clever things to write.”

    What on earth makes you think you’re worth the effort?

  22. shchasm says:

    Will N, your very own words are devastating to your case.

  23. adamwho says:

    Generally good but he fell for the monoculture argument.

    GM crops are no different from traditional or organic crops when it comes to monoculture. The banana example is a red-herring because bananas a clones whereas GM crops generally are not.

    Essentially the monoculture argument is an argument against all industrialized farming which is fine if everybody becomes vegetarians or we have a fraction of the population.

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