Cognitive Daily

[Originally posted in May, 2007]

ResearchBlogging.org“I just didn’t see him” is a claim that’s repeated over and over in accident reports. Drivers earnestly claim that they simply didn’t notice the bicycle/pedestrian/motorcycle they crashed into. The claim is made so frequently that certainly there must be a grain of truth to it. Yet it certainly isn’t the case that car drivers can’t see such obstacles — after all, they can see traffic signals that are much smaller than a bike or a motorcycle.

What they mean to say is that their attention was otherwise engaged — perhaps by a phone conversation, perhaps by other traffic, or perhaps because they were trying to find something — a street sign, a restaurant, a gas station. Human attention is a fickle thing, and in many cases we don’t notice very obvious details changing right before our eyes.

Consider the following movie (QuickTime required): One image will be displayed for a number of seconds, followed by a white screen, and then a second picture — the same image with one very obvious detail changed. Can you spot the change (don’t cheat–just watch it once!)?

Let’s make this a poll:

I’ll give you another chance at the test later on, so don’t repeat it just yet — the point is that it’s often quite difficult for us to notice changes when we don’t know what to look for.

But what about when those changes can literally mean the difference between life and death? Perhaps when we’re driving a car, we’re so attuned to the possibility of an accident that momentary distractions like looking for a street sign don’t detract from our ability to notice hazards. Steven Most and Robert Astur developed a simple, elegant experiment to test that notion.

They asked volunteers to participate in a driving simulation task. The simulator had a steering wheel, gas pedal, and brakes, and volunteers were asked to navigate through city streets, turning whenever an arrow flashed in a particular color — either blue or yellow. The car drove automatically at a constant speed of 30 miles per hour, and the participants were told not to stop unless they were about to hit a pedestrian or another vehicle.

Drivers had to pay close attention to the arrows, because they could change color as they flashed, and they were only supposed to turn when the arrow stopped flashing and was the correct color — immediately before they reached an intersection. After seven successful turns, a pedestrian walked across the street, forcing a stop. The key manipulation, however, occurred after 9 turns. At this point a motorcycle unexpectedly veered into the driver’s path. For half the drivers, the motorcycle was the same color as the arrows they were supposed to follow, and for half the drivers, the motorcycle was the color of the arrows they were supposed to ignore. Was there a difference in stopping time when the motorcycles were different colors? Here are the results:

i-1e00493c8739331e5ee7360323f62746-Most1.gif

When the color of the motorcycle matched the color of the arrows the driver was following, the braking time was significantly faster, and almost no drivers collided with the motorcycle, compared to a whopping 36 percent collision rate when the color of the motorcycle didn’t match the color of the arrows.

Most and Astur conclude that even in a dangerous situation, the attentional set of a driver has an important impact on driving ability. Just as drug users are quicker to spot changes in drug-related items in a photo, so drivers are faster to react to road hazards if they match other items they’re looking for as they drive. So in this case, there’s no difference between a dangerous situation and an ordinary situation; what matters is the particular attentional set at of the driver the time of the incident.

One potential application, the authors suggest, might be on road construction sites: if the color of traffic markers such as cones and reflectors matched the color of worker uniforms and construction equipment, then drivers would be quicker to react to those hazards.

Now back to the demo I started with — can you notice the change in the picture this time? I’m betting a large number of readers will do better the second time they take the test. Go ahead, try it:

Did you see the change this time? Record your response in this poll.

If all goes well, we should see a significant improvement this time. I’ll explain why in the comments — after plenty of readers have had a chance to respond.

[Update: I changed the task to respond to several readers' suggestions that what we may have is a practice effect. See comments 12 and 30 for details]

Steven Most, Robert Astur (2007). Feature-based attentional set as a cause of traffic accidents Visual Cognition, 15 (2), 125-132 DOI: 10.1080/13506280600959316

Comments

  1. #1 Dave R.
    August 4, 2008

    I saw the change immediately.

    My personal theory on why motorists simply don’t “see” cyclists and motorcyclists is because they’re simply not looking for them. They think road = four-wheeled vehicles, and just look straight past bikes. That’s if they even bother to move their heads far enough to be able to see the cycle path.

    Perhaps because I’m a cyclist myself, or perhaps because I pay much closer attention to the road than drivers do.

  2. #2 Greg
    August 4, 2008

    I beg to differ, but this is not an obvious detail.

    This is an irrelevant detail off to one side.

    In a picture like this, with a centrally positioned subject, the obvious details are those in the center.

    Further more, the space around the “changed” object bears the marks of photo manipulation. I believe this causes the peripheral vision to assume no change has been made to the image.

    All in all, I’d have to say this is a pretty poor test to make a point that is probably correct.

  3. #3 Chris Grimes
    August 4, 2008

    I mistakenly thought the 43 had changed the first time, but I wasn’t sure (it was supposed to be obvious) so I clicked no on the poll. The second time around I noticed that the 44 seemed to have been added, before I got to the part where it disappeared.

    Which makes me wonder, is there a difference in these sort of tests when something is added as opposed to taken away?

  4. #4 Nick
    August 4, 2008

    I don’t agree that the change is an obvious one. It is easy to see if if one is looking, but a visually small change in the corner of the photo is hardly significant. None of the objects in the focus of the photo change, and those are the ones that people will be looking at because they’re the object of the photo!

    I would bet that if you changed something more obvious in the picture or if you removed the white frames, everybody would catch the change. There is more at play there than color sensitivity.

  5. #5 The Ridger
    August 4, 2008

    Dave R. is right. I’ve never hit anyone but I’ve lost track of the number of times I’ve thought “Where the HELL did he come from?” Driving is very much an automatic activity – how many times have you driven to a familiar destination and had no memory of the trip? Bikes are simply not something that registers with many drivers – their minds are set to pay attention to “vehicles” and bikes don’t qualify.

  6. #6 Richard Simons
    August 4, 2008

    I am not surprised by this. Years ago when we were buying a new Saab in the UK, the colour we wanted (tan) was no longer available because it had been found to be involved in an unusually high number of accidents. More recently, when I lived in a very bright climate I noticed that blue cars were considerably less visible from a distance than other colours, including black while the tans that had been less visible in the UK were easily seen. It seems the ambient light affects the relative visibility of objects.

  7. #7 Howard
    August 4, 2008

    Daniel Dennett demonstrated the same phenomenon at a lecture in NYC about 10 years ago. The changed detail was more central to the picture, but most of the audience couldn’t see it. His point, as I remember it, was that the process of seeing is not passive. The brain participates and fills in, or deletes details which vary according to attention and expectation.

    That’s relevant to motorcycle accidents, as stated by “The Ridger” above. After reading a variety of accident studies which emphasize visibility, I came to the conclusion that wearing highway signage colors would offer me the best protection against invisibility while motorcycling. My helmet is solid yellow, and my mesh jacket is bright red. Both colors are meaningful on the highway, and the yellow is visible from afar. Neither ensures that somnolent motorists will see you, simply because it’s too easy to dissociate while driving a car. Successful engineering for stability and comfort, as well as distracting cell phones, GPS systems, and Ipods, have created dangers all their own.

    While there’s no substitute for disciplined attention at the wheel, I expect that some engineering genius will soon devise a replacement for it, and people will flock to buy it.

  8. #8 Ryan Morehead
    August 4, 2008

    The quicktime movie is just an example of change blindness. If you google it there are tons of examples, for both flashing a change and slowly fading in something as obvious as an entire building. It’s a well established, robust phenomena that is also very cool.

    I’m guessing using the word ‘number’ in the sentence right before the test primes you to see the difference? I was going to ask how you primed it but then I reread the sentence.

  9. #9 lurker
    August 4, 2008

    I noticed a change, could correctly point to where the missing thing should have been in the picture, but was completely unable to figure out exactly what had been there until the second test.

  10. #10 Ben_Wraith
    August 4, 2008

    I thought something had changed in the place it had the first viewing, but I wasn’t certain so since it was said it would be obvious I voted no.

  11. #11 Alexandra
    August 4, 2008

    The claim is made so frequently that certainly there must be a grain of truth to it.

    You’re kidding, right?

  12. #12 Moe
    August 4, 2008

    I agree with Dave R. #1 that most drivers don’t notice the motorcyclists or cyclists because they don’t look for them. Since there’s no fear of being seriously damaged, on a comparative basis, by a motorcyclist or to a lesser extent a cyclist compared to other 4-wheeled vehicles, one would instinctly pay attention to what could cause harm and/or damage.
    If all drivers had to ride a motorcycle and/or a bicycle as part of obtaining their licenses then less accidents of inattentiveness or unawareness would occur.
    I believe this because I am a biker (motorized and not) and became more aware of motorcycles AFTER I earned my licence for them.

  13. #13 Widdershins
    August 4, 2008

    I have to argue against the whole point put forward by Dave Munger (#12) that “priming” the viewer for numerically-oriented things work. Two small references, when read quickly over by an adept reader, hardly make any impact at all. I was in no way beginning to think in terms of numbers. I personally come here expecting to see a lot of analysis of “numbers,” which should rule out any significant effect of the first number reference. As for the “second,” I was -expecting- to be asked to watch the video a second time. That’s just how it works.

    Maybe it’s just me, who works with numbers an awful lot in daily life and reads briskly and thoroughly without having to consciously analyze every word. But I’d like to think I represent a fair proportion of the readers.

    Just here making a point of sorts. Jolly good study, wot wot.

  14. #14 Pseudonym
    August 4, 2008

    I agree with Widdershins. In fact, I can report that after the description of the study, I was definitely “primed” to look for a change in colour in the second video, which is why I didn’t see it.

  15. #15 Carlie
    August 5, 2008

    I would bet that if you changed something more obvious in the picture or if you removed the white frames, everybody would catch the change. There is more at play there than color sensitivity.

    That one was really subtle, but no, even HUGE changes are missed when your attention is elsewhere. The visual cognition lab at the Univ. of Illinois has a lot of these online. The most famous one was the subject of their paper “Gorillas in our midst”.

  16. #16 Justin Rowles
    August 5, 2008

    I agree with both the study and Dave R’s observation on bikes.

    I was hit by a driver turning across me in Basingstoke, UK, a few years ago. The attending officer informed me that the (mortified) driver’s ‘explanation’ was simply “I wasn’t looking for bikes”.

    Classification sets are a perfect explanation for what the hell was going on in his head – in fact, he said it himself and I never realised how literally I should interpret his words!

  17. #17 JM
    August 5, 2008

    I don’t buy it. The change is small, off to one side, an irrelevant, very minor detail that is not prominent at all in the original (and actually even a little hard to see).

    Sorry, poor choice for a demonstration

  18. #18 Ponder Stibbons
    August 5, 2008

    Transport for London made a great video on how you can fail to see even a relatively large object that you’re not looking for.

  19. #19 Celeste
    August 5, 2008

    My own close encounter with hitting cyclists was because I had a green right of way arrow, and they ran the redlight, much to my surprise.

    I think the most interesting test would be the colors of cars that get hit. Because there’s been many grey mornings where I looked over my shoulder, didn’t see a car, and started to change lanes, realizing at the last second that there was a grey car not running its head lights in the lane. My Grandmother had the most accidents when she had a grey car, they stopped when she had it painted green.

    So I would love to see statistics of car color in different types of accidents. And if I had a grey car, I would almost always have my lights on.

  20. #20 anon
    August 6, 2008

    Pity the poor bikers/cyclists on my daily commute.

    I do not see the change after repeated viewings of both videos.

    Gawd help us all.

  21. #21 Danielle
    August 6, 2008

    I played the darned movie a half dozen times and couldn’t see the change. Had to read the subsequent posts to figure it out. It seems perhaps the change should be described more as “subtle” than “obvious”….

  22. #22 Dave Empey
    August 6, 2008

    Danielle,

    me, too. Glad to know I’m not the only one!

  23. #23 Kelly
    August 7, 2008

    I just posted a blog (and pictures) about a car accident that my 16 year old son was involved in this weekend. A young girl ran a red light at a high rate of speed and his his Tahoe – flipping it over and slamming it into an electrical pole. I don’t think it had anything to do with color…I think she was not paying attention and flat out ran that light. The frustrating thing – the cops automatically assumed it was his fault (since he is a 16 year old white kid)….and it was not his fault. I just thank God he walked away with a few minor scratches!

  24. #24 Bill
    August 7, 2008

    I had to take screen dumps of the before and after and put them up together. Only then did I see what was missing.

    Bill

  25. #25 dave
    August 7, 2008

    a small nuber on the screen is not a motorcycle or a person
    are you kidding me

  26. #26 Chris
    August 7, 2008

    I too had to watch the video over and over again to see the change, and even when I am staring straight at it I can barely see the change. Maybe I need to change my contrast or brightness or something, but even -knowing- it now, I wouldn’t consider it obvious. Maybe I need to get my eyes checked!

  27. #27 Ian Too
    August 8, 2008

    I have to agree with Greg, this is NOT an obvious change at all. I had to watch the video something like five times on the second occasion before I saw the change. Your point is better made by the Transport for London video linked to by Ponder Stibbons, which is brilliant.

    I’m afraid Celeste’s post is typical motorist whinging. While I agree cyclists should obey the rules of the road the same as everyone else, they are not in charge of over half a tonne of blunt instrument. Seeking to shift the blame does not solve the problem.

    Cyclists, pedestrians and motorcyclists are the ones who should heed this research, as they are the ones who are best positioned to benefit from it: wear reds, oranges and yellows. This will help to protect you from people who are far too comfortable and insulated from the road to be safe on it.

  28. #28 Jim
    August 10, 2008

    This effect was way too subtle to prove the point effectively, being primed to look for color change definitely made it nearly impossible for me to notice the change, but it was extremely difficult to notice the change. That number is like a pedestrian in all black crossing an unlit street.

    Oh, and I spend a lot of time on a bike myself, and I just operate under the assumption that I’m invisible to vehicles and act accordingly.

  29. #29 Bob
    August 10, 2008

    It is interesting to read the Photographer Ken Rockwell’s view on this when he discusses ‘how we see’ (see Pattern Recognition):

    http://www.kenrockwell.com/tech/how-we-see.htm

    His argument being that we do not see with our eyes but with our brain, the consequence of this is that even if we are fully attentive to the road and its traffic you may still, even then, not actually see an object which is right in front of you but that you do not expect to see.

  30. #30 B. Jan
    August 11, 2008

    For another take, here’s an article first printed in the Feb. ’95 issue of Airmail, newsletter of the Airheads Beemer Club.

    According to the Hurt Report, 43% of all motorcycle accidents occur as a result of an oncoming vehicle turning left across the path of a rider. Drivers simply fail to recognize the motorcyclist’s right of way. Their typical lament is “I just didn’t see him”.
    You might lament “How the hell is that possible, you were looking right at me you zoned-out space cadet!”
    Some motorcyclists are convinced that drivers deliberately choose not to see us. They believe that drivers resent us because of our lane splitting or shared parking practices. Others suspect that some car drivers must be anally retentive psychopaths who compensate for their fear of riding by driving to kill.
    In the urban rain forests of LA or New York, that may be true. But elsewhere, most drivers really don’t see motorcycles. Well yes, their eyes see us, but the image doesn’t register in the brain. Why is that?
    Many researchers have postulated that the brain is an organ which rejects, as well as gathers information. They believe that if all the information collected by the senses were to register, the brain would experience sensory overload and blow a fuse.
    To prevent that, the brain tends to organize the world into systems; those which are important to the activity at hand, and those which aren’t. The car driver’s brain has learned to exclude the non-essentials, and to focus only on those objects which are a threat to survival. On the road, those objects are predominantly other cars. Because cars are generally wider than they are tall, the brain systematizes threats as objects characterized by horizontal lines.
    Things characterized by vertical lines are excluded from consciousness as non-threatening, extraneous information. Trees, lamp standards, sign posts, bridge abutments, buildings; none of these vertical objects are liable to jump out in front of the driver to threaten his existence.
    Along comes a motorcycle. The driver’s eyes give it a quick visual scan and the brain determines that this too is a vertical object. No threat. No further focus required. Continue replay of last nights debauchery.
    The next thing you know, the driver turns left across your path even though you can see him looking right at you!
    In my early days of riding, an experienced rider hammered me ceaselessly with the message, “You are invisible out there!” I got tired of hearing it. All I heard him say was “Be careful.” I didn’t understand at the time that he was really saying, “To many car drivers, you are literally invisible.”
    Anyone with experience on a bike knows what he was talking about. Many a novice rider has departed the corporal world because he rode his bike the way he drove his car — expecting other drivers to respect his rights.
    Experienced riders have learned that if you don’t want to become horizontal, appear horizontal! How do they do that?
    One way is to use running lights. Many Japanese bikes have orange running lights up front integrated into the signal light housing. That gives some sense of horizontal perspective to car drivers. Some Harleys have a pair of white driving lights alongside of the headlight. That’s more effective due to the increased candlepower.
    I’ve often lamented the lack of stock running lights on unfaired airheads. A single headlight does not give a sense of perspective, and therefore tends to disappear into the background. I replaced the stock signal lights on the front of my Roadster with 4″ round combination signal/running lights. They immediately and dramatically improved the etiquette of the other users of the road. Some Airheads have disparaged the aesthetics of my “emergency” lights, but I find the impromptu installation of a Buick grill far less attractive.
    I’ve replaced the rear running light with a 7″ LED school bus light which flashes when breaking, and added a lot of reflective material to the saddlebags. This also improved the etiquette of other road users (they no longer sniff my tailpipe at stops.)
    I realized the importance of rear conspicuity when I was following a friend home from Barley Therapy one dark evening. To my surprise, rather than focusing on his GS tail light and spacing myself accordingly, I soon found myself gauging my distance from the rear end of the car ahead of him. His pathetic little taillight simply dissolved into the brighter lights of the car, and his bike effectively disappeared.
    If an experienced rider can be so distracted, you can be sure it will happen to car drivers who are not attuned to motorcycles.
    So, get horizontal. Convert your signal lights to signal/running lights. Apply bright, reflective material to your handguards, fairings, saddlebags, jacket and helmet — being sure to make horizontal or diagonal lines rather than vertical ones.
    Most importantly, negotiate our streets and highways as if you truly are invisible. -ed

  31. #31 Will
    August 13, 2008

    The first time I watched this, I didn’t see the first picture long enough to register a change. The second time, I was looking for any change to the store in front.

    Then I read one of the posts explaining how it was a small detail off to the side. I watched it again and immediately found the difference.

    So, the entire article leading up to that actually turned up irrelevant to the video. It was purely the phrasing that stopped viewers from noticing the change, not the difference in colours or whatnot.

    If the article hadn’t said that it was fairly obvious to see, I think more people would have seen it. In scientific studies, it’s better to have unbiased results where you don’t tell them what to look for, unless it’s crucial to the experiment, which in this case it wasn’t.

  32. #32 eddei
    August 18, 2008

    My experience was exactly the same as Chris Grimes in #3. Is this significant?

    I knew the first time that something had changed in my peripheral vision and my attention was drawn to the number 43 that was still there. I wasn’t aware until the second time round that it was the other number no longer there.

  33. #33 Kent Kauffman
    August 19, 2008

    The make safety ads about this over in the UK.

  34. #34 Thomas
    August 21, 2008

    I agree with other posters, the change is not obvious. It’s also very small on my screen…

  35. #35 Tim Reeves
    August 26, 2008

    I saw the change the second time but not the first.
    I think that by not seeing it the first time, I realized it had to be something small and something not in the (interesting) central part of the picture since that’s where my focus was the first time, so the second time, I looked more around the periphery and saw the change.

  36. #36 Nagarajan
    September 17, 2008

    “I just didn’t see him” – “The claim is made so frequently that certainly there must be a grain of truth to it”

    There is a grain of truth allright, but the wording is wrong. It should be “I just didnt notice him”. Ofcourse the motorcycle rider knows that the car driver “saw” him.

    But car driving is a passive activity. People dont concentrate unless there is something on the road to catch attention. For a car turning left, a pedestrian crossing the road which the car doesnt intend to cross does not catch their attention at all. You might not remember weather it was a man or a woman. A bicyclist also catches less attention, no matter where he is headed, as he is slow. A motorcycle though bigger, is unfortunately almost like a bicycle, and can get ignored. You can bet that a full size truck does not get ignored and gets its full deserved attention.

    Forget about right of way… a car would not cross a truck unless they have made eye contact and made sure the truck signals the car through.

  37. #37 Joel
    September 8, 2009

    Modulated headlights cut down the classic vehicle/mc accident rate enormously. This has been proven in many studies. In my own experience in Wash DC and Los Angeles, it was a daily occurence for vehicles in the other direction to fail to see me. Once I put on a headlight modulator, it never happened again in 4 years. Putting a modulator on the mc is worth a hell of a lot more than all the endless theorizing and palavering here. BTW, I have no financial connection with any manufacturer. Also, BTW, when cell phones became popular, the driving became so bad I got rid of my Suzuki 750 bike. Headlight modulators are around $100, around $150 installed, and it’s an easy install for anyone mechanically competent.