Authors: Tom Vanderbilt
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 sentences 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.”
As with the subjects in the counting test who did not see the gorilla, drivers (and particularly drivers talking on cell phones) would be shocked to learn, later, what they missed—precisely those things the in-car cameras are now revealing. “It is striking that people miss this stuff,” Simons said. “At some level it’s even more striking how wrong our intuitions are about it. Most people are firmly convinced they would notice if something unexpected happened, and that intuition is just completely wrong.”
Human attention, in the best of circumstances, is a fluid but fragile entity, prone to glaring gaps, subtle distortions, and unwelcome interruptions. Beyond a certain threshold, the more that is asked of it, the less well it performs. When this happens in a psychological experiment, it is interesting. When it happens in traffic, it can be fatal.
Try to picture, for a moment, the white stripes that divide the lanes on a major highway. How long would you guess they are? How much space would you say lies between each stripe? When first asked this question, I guessed about five feet, with maybe fifteen feet between the stripes. You might estimate six or even seven feet. While the exact length varies, the U.S. standard calls for ten feet, though depending on the speed limit of the road, the stripes may be as long as twelve or fourteen feet. Take a look at an overhead photo of a highway: In most cases, the stripe is as long as, or longer than, the cars themselves (the average passenger car is 12.8 feet). The spacing between the stripes is based on a standard three-to-one ratio; thus, for a twelve-foot stripe, there will be thirty-six feet between stripes.
I use this as a simple example of how what we see is not always what we get as we move in the unnaturally high speeds of traffic. You may be wondering how it is that humans can even do things like drive cars or fly planes, moving at speeds well beyond that ever experienced in our evolutionary history. As the naturalist Robert Winkler points out, creatures like hawks, whose eyes possess a much faster “flicker fusion rate” than humans’, can track small prey from high above as they dive at well over 100 miles per hour. The short answer is that we cheat. We make the driving environment as simple as possible, with smooth, wide roads marked by enormous signs and white lines that are purposely placed far apart to trick us into thinking we are not moving as fast as we are. It is a toddler’s view of the world, a landscape of outsized, brightly colored objects and flashing lights, with harnesses and safety barriers that protect us as we exceed our own underdeveloped capabilities.
What we see while driving is a visually impoverished view of the world. As Stephen Lea, a researcher at the University of Exeter, explains it, what matters is less the speed at which we or other things move than the rate at which images expand on our retinas. So in the same way that we easily observe a person 3 yards away jogging toward us at 6 miles per hour, we have little trouble tracking a car that is 30 yards away moving at 60 miles per hour. The “retinal speed” is the same.
While driving, we get a gently undulating forward view. Things are far away or moving at similar speeds, so they grow slowly in our eyes, until that moment when the car in front suddenly and jarringly “looms” into view (and you notice their bumper sticker:
IF YOU CAN READ THIS, YOU’RE TOO CLOSE
). But now picture looking directly down at the road while you’re driving at a good speed. It is, of course, a blur. This is no less part of the actual environment in which we are driving, but we are physically unable to see it with any accuracy. Luckily, we do not usually
need
to see it to move safely—though, as we shall learn, there are other ways in which traffic puts our visual systems to severe tests.
Traffic illusions actually hit us before we even get in the car. You may have noticed how in movies or on television, the spokes on a car’s wheels sometimes seem to be moving “backward.” This so-called wagon-wheel effect happens in movies because they are composed of a flickering set of images (generally twenty-four frames per second), even though we perceive them to be smooth and uninterrupted. Like the dancers in a disco captured briefly by a strobe light, each frame of that movie captures an image of the spokes. If the frequency of the wheel’s rotation perfectly matched the flicker rate of the film, the wheel would appear
not
to be moving. (“I replaced the headlights in my car with strobe lights,” the comedian Steven Wright once joked, “so it looks like I’m the only one moving.”) As the wheel moves faster, though, each spoke is “captured” at a different place with each frame (e.g., we may see a spoke at the twelve o’clock position on one sweep, but at eleven forty-five on the next). So it seemingly begins to move backward.
As the cognitive psychologists Dale Purves and Tim Andrews note, however, the wagon-wheel effect can happen in real life as well, under full sunlight, when the “stroboscopic” effect of movies does not apply. The reason we still see the effect, they suggest, is that, as with movies, we perceive the world not as a continuous flow but in a series of discrete and sequential “frames.” At a certain point the rotation of the wheel begins to exceed the brain’s ability to process it, and as we struggle to catch up, we begin to confuse the current stimulus (i.e., the spoke) in real time with the stimulus in a previous frame. The car wheel is not spinning backward, any more than disco dancers are moving in slow motion. But this effect should provide an early, and cautionary, clue to some of the visual curiosities of the road.
“Motion parallax,” one of the most famous highway illusions, puzzled psychologists long before the car arrived. This phenomenon can be most easily glimpsed when you look out the side window of a moving car (though it can happen anywhere). The foreground whizzes past, while trees and other objects farther out seem to move by more slowly, and things far in the distance, like mountains, seem to move in the same direction as us. Obviously, we cannot make the mountains move, no matter how fast we may drive. What’s happening is that as we fixate on an object in that landscape, our eyes, to maintain their fixation, must move in a direction opposite to the way we’re going. Wherever we fixate in that view, the things we see before the point of fixation are moving quickly across our retina opposite to the direction we are moving in, while things past the point are moving slowly across our retina in the
same
direction as we’re traveling. (See the notes for a quick demonstration of motion parallax.)