We do this sort of thing all the time—and for good reason. Remembering traffic signs we have seen is not useful to our lives. Steven Most, a psychologist at the University of Delaware, compares the flow of information and images we get in daily life to a stream passing through our heads. Unless we stop to “scoop up” some of that water—or “capture” it with our attention—it will flow in and out of our minds. “Sometimes, you attend to things enough to be aware of them in the moment, but that encoding process isn’t necessarily taking place,” he told me. “The awareness is there but not the memory of the awareness. When attention is distracted enough, it’s even questionable whether we have that momentary awareness.”
The reason we notice things like signs while driving is not as simple as it might seem. The average driver, asked why he saw a stop sign, might say, “Because it was there” or “Because it’s the color red, and humans are hard-wired to see red more easily.” But often we see a sign simply because we know where to look for one. This curious fact was explained by Carl Andersen, a vision specialist with the Federal Highway Administration, in a laboratory filled with eye-catching prototype warning signs in bold new colors like “incident pink.” “If drivers are in an area that they already know, they almost don’t even see the sign, because they already know it’s there,” Andersen said. This is known as “top-down processing.” We see something because we are looking for it. To see things that we are not looking for, like unexpected stop signs, we need to rely on “bottom-up processing.” Something has to be conspicuous enough to catch our attention. “If you’re on one of those divided state highways, the older highways, you’re not expecting to stop,” Andersen said. “You’d better have advance signing and reduce the speed to prepare people for it.”
Drivers actually look at most traffic signs at least twice: once for “acquisition” and again for “confirmation.” Curiously, we do not really read things like stop signs. “Studies have been done where they intentionally misspell ‘stop,’” Andersen said. “Everybody stops and then they drive off. They query the people later and the vast majority never saw that it was misspelled.” (In fact, they may not have even seen it; it’s estimated that one-fifth of our viewing time is interrupted by blinks and what are known as saccades, or our eyes’ rapid movements, during which we are, as one expert puts it, “effectively blind.”) Other studies, in driving simulators, have done things like change “No Parking” signs briefly to stop signs, and then back again. When the signs were at intersections, where stop signs usually are, drivers were more likely to notice the change. When they popped up elsewhere (e.g., at mid-block), drivers hardly ever noticed the change. When the drivers did see the sign change from “No Parking” to “Stop” at the intersection, they did not see it change back to “No Parking.” Their decision to stop, the researchers noted, had already been made.
What does this have to do with real driving? After all, traffic signs do not change capriciously. A lot of things in traffic do change, however, and the question of whether we will notice those things depends not just on how visible they are but, indeed, on whether or not we are looking for them and how much spare capacity we have to process them. In a now-famous psychological experiment, a group of researchers had subjects view a video that showed a circle of people passing a basketball around. Half wore white shirts, half wore black. The subjects were asked to count the number of passes. What at least half the subjects did not notice was that a person wearing a gorilla suit passed right through the middle of the circle of basketball players. They were suffering from what has been called “inattentional blindness.”
The idea that people could not see something as striking as a gorilla in a group of basketball players, although their eyes were locked on the video screen, suggests just how unstable and selective attention is—even when we are giving something our “undivided” attention. “There’s an unlimited amount of information in the world, but our capacity for attending to information is pretty limited,” explained Daniel Simons, a psychologist at the University of Illinois and the coauthor of the gorilla study. “If you’re limited in how many things you can pay attention to, and attention is a gateway to consciousness, then you can only be aware of a limited subset of what’s out there.”
Inattentional blindness, it has been suggested, is behind an entire category of crashes in traffic, those known as “looked but did not see accidents.” As with the gorilla-experiment subjects, drivers were looking directly at a scene but somehow missed a vital part—perhaps because they were looking for something else, or perhaps because something came along that they were not looking for. All too often, for instance, cars collide with motorcycles. One of the most frequently cited reasons is “failure to see,” and these events are so common that motorcyclists in England have taken to calling them SMIDSYs, for “Sorry, Mate, I Didn’t See You.”
Many people assume that “failure to see” means that the motorcycle itself was difficult to see, because of its size or its single headlight. But it may also be that car drivers tend to be on the lookout for other cars when entering an intersection or turning across a lane of oncoming traffic. They may be in a sense “looking through” the motorcycle, because it does not fit their mental picture of the things they think they should be seeing. This is why safety campaigns (e.g., “Watch for motorcycles” or the United Kingdom’s “Take longer to look for bikes”) stress the idea of drivers simply being aware that motorcycles are out on the road. “The common intuition is that we first see things in the world and then interpret the scene in front of us,” said Most. “What this work shows is that it’s possible that the idea you have in mind actually precedes the perception and affects what you see. Our expectations and knowledge of what’s in a scene influence what we see in a scene.”
These expectations might also help explain the troublingly high numbers of emergency vehicles that are struck on the highway, even as they sit on the shoulder with their lights flashing brightly (and despite the fact that most places have laws requiring drivers to change lanes or slow down in the presence of an ambulance). These incidents are so common that the term “moth effect” has been coined for them. The idea is that drivers are lured to the lights, like moths to a flame.
What could cause a moth effect? There are many theories, ranging from arguments that we tend to steer where we look (which raises the question of why we do not drive off the road every time we see something interesting) to the idea that humans instinctively look toward light (ditto). Other researchers have argued that the fixation of attention on the roadside leaves drivers less able to judge their position in the lane. Many moth effect crashes involve alcohol-impaired drivers, perhaps no surprise in light of work that suggests that alcohol has a particularly deleterious effect on our eyes’ ability to perceive depth or direction while we are moving.
The simplest explanation may be that most drivers, upon seeing a car on the highway, assume that it is moving at the same high speed as everyone else—and cars with flashing lights are usually moving even faster than that. One study, conducted in a driving simulator, showed that drivers reacted more quickly when stopped police cars were parked at an angle to oncoming traffic, rather than straight ahead in the direction of traffic. As the two vehicles were essentially equally conspicuous, the reason the angled car was seen sooner had less to do with visibility than in how the drivers interpreted what they saw: a car that was obviously not moving in the direction of traffic. (This ability to interpret seemed to be a by-product of driving experience, as novice drivers had the same reaction times for both cars.)
Even when we see an unexpected hazard, the fact that it’s outside our “attentional set” means we are slower to react to it. This is demonstrated in a classic psychological test for what is known as the “Stroop effect.” Subjects are shown a list of color names; these words are printed in the same color as the name as well as in other colors. Naming the color a word is printed in, it turns out, typically takes longer when the word does not match
the color; that is, it takes longer to say “red” when the word printed in red is “yellow” than when it’s “red.” One argument for why this happens is that while reading is for us an “automatic” activity, naming colors is not. The automatic gets in the way of the less automatic (as with the stereotyping studies in Chapter 1). But other theories suggest that attention is involved. That we can name the correct color when the word itself is “wrong” suggests that we can train our attention on certain things; yet the fact that it takes us longer to do it shows that we cannot always screen out the things on which we are not focused (i.e., the word itself).
What this means for traffic was highlighted in a study by Most and his colleague Robert Astur. Drivers on a computer driving simulator, navigating through an ersatz urban environment, were asked to look for an arrow at every intersection telling them where to turn. For some drivers, the arrow was yellow and for others it was blue. At one intersection, an approaching motorcycle, itself either blue or yellow, suddenly veered in front of the driver and stopped. Drivers’ reaction times to slam on the brakes were slower—and their collision rates were higher—when the motorcycle was a different color than the arrow. In a purely bottom-up form of processing, we might expect the motorcycle to stand out because it is different; but because we are looking at the scene from a top-down perspective, the odd-colored motorcycle is less visible because it is different from those things for which we are searching.
This attention disorder could also help explain the “safety in numbers” phenomenon of traffic, as described by Peter Lyndon Jacobsen, a public-health consultant in California. You might think that as there are more pedestrians or cyclists on a street, the more chances there are for them to be hit. You are right. More pedestrians are killed by cars in New York City than anywhere else in the United States. But as Jacobsen found, these relationships are not linear. In other words, as the number of pedestrians or cyclists increases, the fatality rates per capita begin to drop. The reason, as Jacobsen points out, is not that pedestrians begin to act more safely when surrounded by more fellow pedestrians—in fact, in New York City, as a stroll down Fifth Avenue will reveal, the opposite is true. It is the behavior of drivers that changes. They are suddenly seeing pedestrians everywhere. The more they see, typically, the slower they drive; and, in a neatly perpetuating cycle, the more slowly they drive, the more pedestrians they effectually see because those pedestrians stay within sight for a longer period.
And so New York City, when one considers how many pedestrians it has, is actually one of the safest cities in the country for walkers. (One study, looking at 1997–98 figures, found the Tampa–St. Petersburg–Clearwater area to be the most dangerous for pedestrians.) To cite another instance, the Netherlands has a much lower fatality rate per mile traveled for cyclists than does the United States. It is not likely that Dutch cyclists are any more visible in terms of pure conspicuity; they rarely wear reflective clothing, favoring stylish black coats instead, and instead of flashing lights their bikes carry things like tulips. Nor do the Dutch more regularly wear helmets than American cyclists; the reverse is actually true. Perhaps the Dutch just have better bike paths, or maybe the flat landscape makes it easier for drivers to spot cyclists. But the most compelling argument is that Dutch cyclists are safer simply because there are more of them, and thus Dutch drivers are more used to seeing them. Dutch culture may be quite different from American culture, but the “safety in numbers” theory also holds for comparisons within the United States—in Florida, for example, Gainesville, a college town with the highest cycling rate in the state, is in fact the safest place to be a cyclist. The lesson: When you see more of something, you’re more likely to see that thing.
In the gorilla experiment, an added condition made subjects less likely to see the gorilla: when their job got harder. Some subjects were asked to count not just passes but the types of passes—whether they were “bounce passes” or passes made in the air. “You’ve made the attention task that much harder, and used up more of your available resources,” Simons said. “You’re less likely to notice something unexpected.”
In driving, you might protest, we do not do such things as tally basketball passes. Still, there may have been times when you were concentrating so much on looking for a parking spot that you did not notice a stop sign; or you might have almost hit a cyclist because she was riding against traffic, violating your sense of what you expected to see. And there is another activity, one that we increasingly often indulge in while driving, that closely resembles that very specific act of counting basketball passes: talking on a cell phone.
Let me ask you two questions: What route did you take to get home today? And what was the color of your first car? What just happened? Chances are, your eyes drifted away from the page. Humans, perhaps to free up mental resources, tend to look away when asked to remember something. (Indeed, moving the eyes is thought to aid memory.) The more difficult the act of remembering, the longer the gaze away. Even if your eyes had remained on the page, you would have been momentarily sent away in a reverie of thought. Now picture driving down a street, talking to someone on a mobile phone, and they ask you to retrieve some relatively complicated bit of information: to give them directions or tell them where you left the spare keys. Your eyes may remain on the road, but would your mind?
Studies show that so-called visual-spatial tasks, such as rotating a letter or a shape in one’s mind, cause our eyes to fixate longer in one place than when we are asked to perform verbal tasks. The longer the fixation, the thinking goes, the more attention we are devoting to the task—and the less we’re giving to other things, like driving. The mere act of “switching” tasks—like moving from solely driving to talking on the phone while driving or, say, to changing whom we’re speaking to within the same cell phone call via call waiting—takes its toll on our mental workload. The fact that the audio information we are getting (the conversation) comes from a different direction than the visual information we are seeing (the road ahead) makes it harder for us to process things. Bad reception on the phone? Our struggle to listen more carefully consumes even more effort.
Now replace the gorilla of the basketball experiment with a car making an unexpected turn or a child on a bike standing near the side of the road. How many of us would see it? “Driving’s already attention-demanding enough—if you add in the cognitive demands of talking on a cell phone, you’re taking away whatever limited resources you had, and you’re that much less likely to notice something unexpected,” Simons said. “You might be able to stay on the road just fine, and you might be able to stay the same distance behind a car on the highway, but if something unexpected happens—a deer runs into the highway—you might not react as easily.”
The notion that we could miss unexpected things while talking on a cell phone is powerfully demonstrated by our seeming failure to notice the expected things. Two psychologists at the University of Utah found, after running a number of subjects through a simulator test, that drivers not talking on a cell phone were able to remember more objects during the course of the drive than those who were. The objects ranged in their “driving relevance” that is, the researchers ranked speed-limit signs and those warning about curves as more critical than Adopt-a-Highway signs. You might suspect that the cell phone drivers were just filtering out irrelevant information, but the study found no correlation between what was important and what was remembered. Most strikingly, the drivers using cell phones looked at the same number of objects as the drivers without cell phones—yet they still remembered fewer.
Drivers using a cell phone, as noted in the hundred-car study, tend to rigidly lock their eyes ahead, assuming a super-vigilant pose. But that stare may be surprisingly hollow. In a study with an admittedly small sample size, I took the wheel of a 1995 Saturn one day at the Human Performance Laboratory at the University of Massachusetts in Amherst, and got set for a virtual drive in the lab’s simulator. While I drove down a four-lane highway, a series of sente
nces was read to me via a hands-free cell phone. My task was to first judge whether the sentences made sense or not (e.g., “The cow jumped over the moon”) and then repeat (or “shadow,” as researchers call it) the last word in the sentence. As I did this, the direction of my gaze (among other things) was being monitored via an eye-tracking device mounted to a pair of Bono-style sunglasses.
When I later watched a tape of my drive that plotted where my eyes had been looking, the pattern was striking. Under normal driving, my eyes danced around the screen, taking in signs, the speedometer, construction crews in a work zone, the video-game landscape. When I was on the phone, trying to discern whether the sentence made sense, my eyes seemed to train on a point very close to the front of the car—and they barely moved. Technically, I was looking ahead—my eyes were “on the road”—but they were gazing at a place that would not be useful in spotting any hazards coming from the side or even, say, determining whether the truck several hundred feet ahead might be stopping. Which is exactly why I smashed into its rear end. “You were driving like a sixteen-year-old” is how Jeffrey Muttart described it to me.
Our eyes and our attention are a slippery pair. They need each other’s help to function, but they do not always share the load equally. Sometimes we send our eyes somewhere and our attention follows; sometimes our attention is already there, waiting for the eyes to catch up. Sometimes our attention does not think that everything our eyes are seeing is worth its time and trouble, and sometimes our eyes rudely interrupt our attention just as it’s in the middle of something really interesting. Suffice it to say that what we see, or what we think we see, is not always what we get. “This is the reason the whole ‘keep your eyes on the road, your hands upon the wheel, use the hands-free handset’ idea is a silly thing,” Simons said. “Having your eyes on the road doesn’t do any good unless your attention is on the road too.”
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