How to Do the “Step-and-Slide”: A Cognitive Scientist on the Rules of Avoidance, Alignment, and Attraction for Deft Urban Walking
By Maria Popova
Just like the most oft-employed metaphor for the human body is that of a machine, the city is most commonly and comfortably likened to a living organism. But nowhere does this metaphor spring to life more viscerally than on the busy sidewalk of a densely populated metropolis, where people, as if controlled by the strings of an invisible and highly skilled puppeteer, manage to move in a giant, self-correcting swarm without colliding with one another. It is a remarkable sight to behold, a daily miracle in which we find ourselves participating as sophisticated automata, without stopping — not literally, of course, which would be disastrous for this whole invisible dance — to appreciate the astounding mechanisms that make this phenomenon possible.
In On Looking: Eleven Walks with Expert Eyes (public library) — the same magnificent read, my favorite in ages, that demonstrated how much what we call “reality” is framed by the limitations of our selective attention — cognitive scientist Alexandra Horowitz examines the special skill of the urban pedestrian: a deft and intuitive maneuver known as the “step-and-slide,” which turns out to be the secret to urban swarm management.
One of the eleven experts with whom Horowitz strolls around a city block to learn new ways of seeing is Fred Kent, who founded the Project for Public Spaces thirty-five years ago after collaborating with the great William “Holly” Whyte on understanding the social life of urban spaces. Thanks to Kent, who has been observing the step-and-slide for years, Horowitz breaks down this necessarily mundane yet infinitely curious move, which researchers identified after innumerable hours of watching people walk past one another in the street:
If sidewalk traffic is dense and collision seems imminent, we pull this two-step pedestrian-dance move. While striding forward, the walker turns ever-so-slightly to the side, leading with his shoulder instead of his nose to turn the step into a side-step. We twist our torsos, pull in our bellies, and generally avoid all but the mildest brushes of other people (and if we do brush against someone else, we keep our hands close to our body and our faces turned away from one another.)
But how and why are we able to perform the step-and-slide so effortlessly? Horowitz explains:
One reason all of our step-sliding, pedestrian-jigging works is that we are regularly looking — ahead and at each other. We do not just look to see who is there; we constantly, steadily look to calculate how we need to move relative to those around us. We regularly turn our heads back and forth, to the left and right, surreptitiously peeking at who is behind us or to our sides. When our heads face forward, we survey the scene ahead of us. Our eyes make small saccades. Within a long oval projecting forward from our feet to about four sidewalk squares ahead, we quickly note the direction and pace of anyone headed our way. We also glance at others’ faces, which tell us if they are likewise looking forward into their own long ovals (and whether they are reacting to something surprising or alarming that might be behind us). There is information in the angle of others’ eyes and the turn of their head. Most of the time, people are looking where they are going: gazing straight ahead. But they begin actually inclining toward their destination when it is in sight. Should someone seem to peer over to the doorway of the building down the block, more likely than not, he will walk there directly. Or just follow his head: we all make anticipatory head movements when we are going to turn a corner. Our heads lead our bodies by eight degrees and as much as seven steps, as though all in a hurry to get around the bend. Watch a walker’s head and you can predict his path down to a single step. We learn this without anyone teaching us, and without knowing we know it.
This, of course, begs the inevitable question of what happens when our voluntary modern-day relinquishing of looking — those glowing rectangles that mesmerize us so with their siren calls of email, Facebook, Instagram, tweets, texts, and the like — hinders the very ability to notice the body language and indicative eye gazes of others, which are so critical to the performance of this collective dance. In other words, for every person who walks into a pole while staring at her iPhone, there are several sidewalk peers whose personal step-and-slides have been set off balance by her inability to master her own. This pattern, Horowitz agrees, is an especially malignant form of contemporary social ill that cripples a central convention of urban life:
The importance of this “looking” in the success of the dance comes into play with the relatively new species of pedestrian on the street: phone talkers. Their conversational habits change the dynamic of the flowing shoal. No longer is each fish aware, in a deep, old-brain way, of where everyone is around him. The phone talkers are no longer even using their fish brains: they have turned all their attention to engaging with the person on the phone. They block out their sense of someone walking too close; they fail to look into their walking ovals and step-slide out of the way. They no longer follow the rules that make walking on a crowded sidewalk go smoothly: they do not align themselves (they swerve); they do not avoid (they bump); and they do not slip behind and between others (they blunder). They stop minding the social convention to stay to the right, and weave across lanes of traffic. Texters are as bad or worse: they fail to even move their heads before turning, since they are slumped over to monitor their texting thumbs.
So how does one master the step-and-slide and avoid collision? Horowitz offers three simple, research-backed rules — known as “avoidance,” “alignment,” and “attraction” — for honing your acumen at this pedestrian jig, essential for balancing personal space against public space, personal pace amidst public pace:
- Avoid bumping into others (while staying comfortably close). What counts as “comfortably close” — an animal’s “personal” space — will vary by species; what is similar for all animals is that if you follow only this one rule, it forces you to attend and react to the behavior of those in your vicinity. And that is the essence of what is called swarm intelligence: everyone must make movements that are sensitive to everyone else.
- Follow whoever is in front of you. “Whoever” need not know where she is going: she may herself be following another. And so on and so on, until you reach the very head of the pack. Even there, the animal at the leading edge is neither leader nor sovereign. In flocks and schools, the role of leader is constantly changing hands. For only a moment will she determine the group’s direction.
- Keep up with those next to you. Everyone must speed or slow with attention to those around them. This seems like an impossible calculation, until you realize how little effort you have to pay to walk next to someone else down the street, never once considering how you will be able to keep at the same pace.
These rules of “avoidance,” “alignment,” and “attraction” — keeping apart while staying together — are sufficient to explain all herd, school, flock, and swarm behavior. Artificial intelligence scientists have created animations of mindless “boids” programmed with just these rules: their behavior matches that of swooping sparrows and swarming ants.
On Looking: Eleven Walks with Expert Eyes is absolutely fantastic — necessary, even — in its entirety. Sample more of the book’s wisdom and mesmerism here. For more on the curious dynamics of city-dwellers, see Whyte’s timelessly insightful The Social Life of Small Urban Spaces.
Public domain images via Flickr Commons
Published September 9, 2013