Jun 18 2010
Change Blindness
It should come as no surprise that we don’t notice everything that we see. We all experience this on a regular basis – there is a great deal of visual information in our field of view but we only pay attention to a small fraction of it. Yet at the same time something within our vision can capture our attention if it flashes, moves, or otherwise changes dramatically enough. Interestingly, despite our common and frequent experience with the limitations of our own visual attention, people tend to have overconfidence in their ability to notice details and are often surprised when an important detail goes unnoticed.
Here are some fun examples of a what neuroscientists call change blindness. First from Richard Wiseman – the color changing card trick. And here is a great one from Derren Brown. Failure to notice one person being swapped for another may even have implications for eye-witness testimony.
Change blindness is the failure to notice a visual change in our field of view. It is closely related to but distinct from inattentional blindness, which is a failure to notice an element of a scene at all (not specifically a change).
Scientists have been exploring the nature of change blindness. As an aside, I am always amazed at the depth of detail I can find in any narrow scientific question. It seems that there is almost always a small group of researchers who have delved to an incredible depth on even the smallest question. And that is what I found with the change blindness literature. But I think I have wrapped my head around the major themes of this research – spurred by a recent study using computer technology to aid in more accurate testing for change blindness.
Top Down vs Bottom Up
Also as with many scientific questions, there are competing views that both likely contain an element of truth. With change blindness the two competing views are described as the top-down hypothesis and the bottom- up hypothesis, referring to what it is about the change of a scene that grabs our attention. Top down theories involve our understanding of the context of a scene. In the new study they give the example of searching for a computer in a picture of an office. Our attention goes to the desk because we understand that a computer is most likely to be found there.
Bottom up theories focus on the visual salience of image components such as contrast, movement, and lighting – the more basic elements of our visual processing.
It seems that both of these process are at work. Depending on our goal, we use our top-down knowledge of what should be in a scene to search for something of interest. But even in the midst of such a task our attention can be drawn to a high contrast object or something that begins to flash in our visual field. This makes sense from a function point of view – we need to balance out ability to focus our visual attention but still notice important changes in our visual field. But this is also a trade off, like many functions in biology. The more we focus on details, the less we may notice change, and the more we attend to the overall scene, the less we can attend to details and context.
We very much have limited visual and cognitive processing resources, and we allocate them as needed – but we can’t do everything. You have probably noticed this in everyday life. Sometimes you may be very focused on something and may be completely inattentive to events in your environment – what we might call distracted. At other times you may be “on alert” and attentive to everything happening around you.
In any case – researchers are dickering over the relative contribution of bottom up vs top down factors in change blindness. The recent study makes two contributions to this ongoing debate. First, they argue that prior research looking at the contribution of top down factors in change blindness were contaminated by unintentional bottom up changes as well. For example, when one object was manually removed from an image or replaced with another object (a top-down context change), the salience of the picture (contrast, etc.) may have also been inadvertently altered. They therefore propose a computer algorithm to makes changes to a scene without changing the overall visual salience of the scene, and therefore better separating these two variables.
Computer Study
What they did was show subjects a scene followed by a gap and then followed again by the same scene with one subtle change. This is a flicker test, and prior research has shown that it is more difficult to notice changes with the gap in between than when one scene is immediately replaced with the changed scene – the flicker disrupts our ability to notice the change (here in an example). In this video accompanying the BBC article on the study they show some of the pictures used in the study.
With their improved method the authors found that people are more sensitive to removing or replacing an object in a scene than they are to color changes (which explains the color changing card trick).
Conclusion
The details of this research are interesting and may lead to practical applications, such as designing road signs that better grab drivers’ attention. It will likely also be used by marketing companies to design ads and commercials that will demand our attention – the attention of consumers is a commodity that companies will pay for.
For most people, however, the big picture is important – we have a limited capacity to attend to details or changes in those details. Yet, we are overconfident in our abilities. This extends to memory as well as sensory attention. This overconfidence causes much mischief, such as placing excessive faith in eyewitness testimony. It also contributes to the anecdotal evidence that comprises the bulk of the arguments made for many paranormal beliefs. When people see a strange object in the sky, for example, and think it is an alien spacecraft, or at least a genuine mystery, they are generally being overconfident in their ability to have noticed important details that might have provided a more prosaic explanation.
Understanding change blindness is therefore important to the humility inherent in a scientific and skeptical point of view. It is also very helpful in getting husbands out of hot water when they fail to notice a change in their wife’s hair color or style. Well, maybe not.
18 Responses to “Change Blindness”
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Good to see them pushing the psychophysics in the right direction with this research.
I always loved the change blindness studies they put in the Sunday comic pages every week, those “spot the difference puzzles” where you have to detect what is different between two pictures. I suppose they introduce a flicker the old fashioned way by having two pictures side-by-side that you have to saccade between. (Example here).
I saw a related one last week that was even harder: they had four pictures that all superficially looked the same, but the game was to pick the two that were identical. It was even harder.
Here’s an interesting test of selective attention by Prof Daniel Simons. If you’ve never seen it before, try first here:
http://viscog.beckman.illinois.edu/grafs/demos/15.html
There’s also a great resource/database on change detection, including some demonstrations of gradual change at:
http://viscog.beckman.illinois.edu/change/
Fictional detectives and heros often “see it all in a glance” or notice the tiny little details. But I wonder if that is only in fiction or if someone can be trained to be that focused.
Or even if certain people are just “built” to have less change blindness.
I am very unobservant. But since I hate this about myself, I have been trying to train myself to be more observant and “detail” oriented.
I started to play MS Majhong and “spot the difference” puzzles to try and teach myself to find details more quickly.
I think I am a bit improved, but not dramatically.
I’m fascinated by the science of how we see the world. I always wonder how much a person’s sight factors into their intelligence, world view, personality, and tendencies.
Anecdote alert!…
For example, I had 20/15 vision with the aid of glasses and contacts until getting LASIK around age 24. There were some complications which led to several surgeries in each eye. Some resulted in far sightedness which was then overcorrected, resulting in near sightedness, with each eye being different from the other at almost every step.
The near/far sightedness and resulting halos had a definite effect on how I felt and saw the world. The halos produced a pretty if not distracting abberration around light sources. And while each eye was not very far from 20/20 after the final procedure, it seemed to take a fraction of a second longer to focus and reconcile the images. Almost as if my brain was spending a little more energy and time processing the information being fed in through the eyes.
The specific questions I’m getting to are:
1) I wonder if a person born with an eye shape that results in halos all their life would be more likely to “see” ghost orbs and other such anomalies.
2) How much does less than perfect vision affect mental performance like memory, reaction time, facial recognition and others? Could the causes of poor performance in these areas be separately attributed to visual defects as opposed to mental defects? Are there studies that correlate how variables in visual acuity can affect a person’s personality and mental abilities?
Just wondering aloud. Thanks for the post
Very interesting. Are there any differences in change blindness for people from different cultures?
I remember hearing on NPR about some study a while back where people were shown an object among other objects for a few minutes and then asked questions about the items. People from “western” cultures like the US were better able to describe properties of the object itself, while people form “Eastern” cultures were better able to describe the relationship of the object to the other objects (bigger than, above and left of, redder than, etc).
The idea was that people from densely populated eastern societies are conditioned to be more concerned with their relationship to their surroundings and the group while Americans are conditioned to be more focused on individuality and less concerned with our contextual relationships.
@ Shelley-The videos on that site were interesting. The ones that really tripped me up were the gradual changing scenes. It is pretty arresting to realize that something can be added subtracted or changed right in full view,and you can still miss it,even when you are expecting a change.
“It is closely related to but distinct from inattentional blindness, which is a failure to notice an element of a scene at all (not specifically a change).”
I wonder why these are considered distinct. It seems that at least sometimes they can be part of the same phenomenon. How can a change in a scene be noticed if you don’t notice the object in the first place due to inattention blindness? Perhaps I am just pointing out a difficulty in separating out to distinct phenomena, because I’m not that familiar with the research.
“I wonder why these are considered distinct. ”
Because we much greater difficulty noticing a change in colour of an object than the total absence of that object
“Because we much greater difficulty noticing a change in colour of an object than the total absence of that object”
Well my point was that you can’t notice a change if you don’t notice that it is there in the first place. Unless there is an assumption that the object that changes is noticed in the first place, but some of the examples I’ve seen don’t seem to assume this.
… which implies to me that they are not truly distinct in real world applications.
To elaborate…In the flicker example above, the change is actually an object that disappears. It is very difficult to notice the change at first, but as soon as you are aware of the object you can’t help but see the change. So there seems to bea possibility of some overlap
You may be aware of a recently published book relevant to the topic. Chabris & Simons (2010). The invisible gorilla – and other ways our intuitions deceive us.
ccbowers:
FWIW (despite being very interested in these issues, I have neither credentials nor expertise), I tend to agree with you.
Alva Noe and Kevin O’Regan have argued (as I understand them) that contrary to popular opinion (“popular” within the relevant community, that is), the brain doesn’ t construct “representations” of the whole visual scene and compare the representation at one time with the representation at another time. Instead, the vision system constantly probes parts of the visual scene for new information, eg, changes. It seems reasonable to assume that at least in some circumstances the probing is goal-directed, ie, focused on parts of the scene relevant to a specific purpose.
For example, in the video of the basketball players the initial “counting” question focuses attention on the white-clad players, which motivates the viewer to direct attention away from the black-clad players. And surprise! the gorilla suit is black. This seems to raise the question – your question, if I understand it – whether we miss the gorilla because of inadequate attention or because of change blindness (the scene, after all, does “change” when the gorilla walks across the FOV). And my answer would be that since the black-clad players – and hence, the black gorilla – are a distraction with respect to answering the question at hand, what actually happens is that attention is extremely well-focused, and that happenings in the scene that are associated with black “objects” are dismissed as an irrelevant distraction.
I don’t know how other people fared after being made aware of the gorilla, but despite trying as hard as before to focus on the white-clad players, I was unable to NOT see the gorilla, and to see it quite clearly. Ie, the introduction of the new “did you see” question seemed to have served to degrade attention with respect to answering the initial question.
Your observation about the flicker experiments seems to be consistent with this. Because the goal initially is vague (“find the change, whatever it might be”), the viewer has to sample the whole scene sequentially. But once it is known where to focus attention, it seems impossible to miss the change.
Great article as always, Steve.
Do you have a perspective on the use of CRT or LCD monitors for computer studies? I have a couple of friends studying psych who have mentioned that it’s better to have a CRT for ‘experiments’ (as their common word for testing these kinds of phenomena).
Given LCDs have a refresh rate of sub-5ms these days I wouldn’t have thought it would make any difference.
I wonder if there is a difference in the frequency or degree of change blindness in men and women. I, for one, notice very little in details around the house–my wife could probably move the kitchen into the bedroom and I wouldn’t be aware of it for a week. I, however, can move a pencil a little to the left and she wonders what went wrong. Seriously–is there an x-linked component to the intensity of attention to detail?
Can anyone see the changes in the Change blindness demo (the one with the bunny)? I’ve been staring at it for at least 5 minutes and can’t see the change. Maybe I need to be in a study.
George
Change blindness picture spoiler alert:
georgepseifert-
In the lower right section of the picture there is a light green flower near the stem of the plant that appears and disappears.
I think all those people in the Darren Brown video recognized the change, but simply didn’t make a big deal out of it. Most people’s reactions to tricks is just to annoyingly go along with it.