It would be a mistake to think that all that a cane user experiences is the information borne through the cane, though. After a half block of supervising Gordon's left-veering and straightening behavior (never once needing me to help her), I saw an interesting scene ahead. It was the end of the block. Would Gordon see it?

The corner building was another grand old prewar apartment house-tall, well bricked, and shade lending. The moment we stepped past its corner, Gordon stopped.

"Are we at the end of the block?"

I grinned. "Right!" I a.s.sumed that she had heard her way to that conclusion. The street intersected with a larger boulevard, full of car and truck activity and its accompanying horns and hubbub. But I was wrong.

"I could feel it."

"Feel it?"

"The breeze."

Indeed, there was a subtle but noticeable current of air traveling along with the traffic, going north to south. City dwellers grow familiar with the superficial appearance of the buildings on their regular walks to and from their home and work, but there is another, unseen architecture that is nearly as consistent: the winds. Though winds change with weather, the shapes of large structures like buildings act on those winds in reliable ways. Urban microclimates are created largely by the changes in airflow induced by the man-made environment. In a city like this one, full of right angles between streets, a turned corner almost always brings with it a change in the flow of air. Though the direction and temperature of the air might vary by hour or day, the contrasting orthogonal airflow is more reliable than the particulars of street or sidewalk activity.

The urban windscape manifests a Who's Who of physics phenomena, involving forces and flows described by the Bernoulli principle, the Venturi effect, turbulence, and the properties of eddies and vortices. Streets lined by tall buildings become wind tunnels, through which the air being blown around in a large, wide-open area accelerates dramatically as it gets pushed into the small canyon of the street (the Venturi effect). Thus, winds over the rivers flanking Manhattan Island speed down side streets on land. No one who lives along one of these side streets needs to be told that the wind plasters the face and requires a whole-body lean to push through.3 This occurs whether the streets are lined with particularly tall buildings or not, but in the former case, the winds blow faster for farther. Tall buildings create other wind effects: winds that hit high on a building rush down its face, sometimes creating enough pressure to make pa.s.sage in and out of the doorway difficult. Sheer gla.s.s towers can pull air not just down, but also up from below (the Bernoulli principle)-as well as lift any skirts being worn in the vicinity. The edges of buildings have their own wind phenomena: circling eddies of air appear as air travels around the building's corner, s.n.a.t.c.hing hats off approaching heads. Combine enough of these forces, and a vortex may appear, an independent whirlwind which lifts fallen leaves, discarded plastic bags, and city debris in its path down the street.

Gordon and I turned left, and I watched as people took a wide berth around us. With her cane and me riding sidecar with a microphone, no one could miss us. I wondered how she fared when there was not someone walking along with her. In particular, thinking back to my walk with Kent, I asked her, what about the cell-phone users?

Walking-while-talking (on phones) or texting is now commonplace, as is decrying the activity (unless you are doing it yourself). The decriers can be a sympathetic lot. When Oliver Sacks lost peripheral vision on one side, the West Village outside his home became suddenly unnavigable. In particular, he bemoans the hazards presented by people rushing hither and yon, "so preoccupied with cell phones and text messaging that they themselves are functionally deaf and blind." For people like Sacks, the behavior of people not considerate enough to look out for others makes the sidewalk a perilous, stressful place.

The trouble with cell phones on the street is that, though "talking on the phone" and "walking" do not seem cognitively complex, each requires attention. Even before there were retail mobile phones, there were studies using them to test distraction. A 1969 study asked subjects to listen to sentences on phones while driving to see if this distraction impaired their judgment and increased the mistakes they made (it did, on both counts: including mistakes in judging if that gap up ahead was big enough to fit one's car through). The reams of subsequent research on how cell-phone use impairs driving ability has led to bans in most states on doing these activities simultaneously-and to the subsequent upsurge in hands-free headset use (solving only part of the problem).

It is understandable that cell-phone use is problematic when doing something requiring concentration, such as driving at breakneck speeds down an interstate highway. But even walking down the street requires concentration, albeit of a more unconscious sort. Simply by having open eyes, pedestrians notice changes in the environment: a handcart being pulled across the sidewalk, an approaching carriage, a wayward long-leashed dog. Without consciously intending to, we make small adjustments. My walk on Broadway with Kent had been a testament to the success of this in keeping us, as most people, from colliding.

With Gordon, I became more attentive to the violations of the pedestrian rules. I noticed that people tended to slow down when using their phones. Rather than a benefit, this could be a menace, as the pace of pedestrian traffic is usually instinctively adjusted by pedestrians considering each other's pace and route. I saw examples of cell-phone walkers weaving, violating the time-honored stay-to-the-right street rules. Most critically, they were not checking: they did not look up. Walkers typically acknowledge each other with eye contact, enforcing the social rule of at least attempting to mind other people's paths. Cell-phone talkers are less likely to notice others, let alone acknowledge them. Nor do they notice something unusual at their feet, or even see a unicycling clown with a red nose and purple jumpsuit on their route (as one study tested). The pedestrian dance of Fifth Avenue is replaced by the herky-jerky stop-and-go dance practiced by poor dancers-and by pedestrians who suddenly find someone directly in front of them. With their eyes focused not on the street, but on the conversation in their ears, the skill we have developed in navigating pedestrian traffic is wasted.

So how did Gordon feel about these cell-phone users? They were always a hazard, she agreed, describing a number of full-body collisions because of distracted walkers. As she spoke, a young woman on a cell phone was gaining on us from behind. Her laughter was punctuated by periods of silence presumably filled by the person chatting into her ear. Gordon stopped. She often slowed to a stop herself when she wanted to make a point. The cell-phone laugher pa.s.sed us.

"But one thing I will tell you. They make it easier to hear people."

For a noisy species, human pedestrians can be awfully silent. Walking with Gordon, I began to notice the numbers of sneakered, light-footed walkers almost stealthy in their pa.s.sage by us. There are, to be sure, a number of people who give away their presence in their manners or clothing. There are the flip-flopped, the high-heeled, and those whose boots or hard-heeled shoes gently clip-clopped. There are the key jinglers, the pocket changed; the package burdened, the wheely suitcased; the panters, the grunters, the hummers, whistlers, and singers. You hear the foot sc.r.a.pers and scuffers coming; and you can smell the perfumed or smoking brushing by. You hear the suspiration of a bag strapped across and banging against the body. The corduroyed.

Apart from these people projecting their path ahead of themselves, most people are remarkably quiet: the electric cars of pedestrian traffic. So people on cell phones may be a nuisance, but to the visually impaired, they are also beacons, sending out information about where they are (and what they are doing). To Gordon, they served to identify at least some of the presence in the otherwise unknown s.p.a.ce around her. She appreciated their uncivil loudness.

They also were giving Gordon something I might not have heard (or, at least, attended to): details about themselves, conveyed in their voices. A voice carries a large amount of information about the speaker-from the person's s.e.x to his size, ethnicity to age, even level of fitness (we can all hear the habits of the cigarette smoker or the physique of the obese in their voices). Voices carry emotional information, too, from disgust to sadness to surprise, even when speaking words that have nothing to do with emotional state. Most of us are quite good at naturally distinguishing emotions in vocal sounds. Potentially, the blind could be even better, although they are not always. With this in mind, the Belgian Federal Police force recently hired a few blind officers especially attuned to a.n.a.lyzing voices, especially on wiretap recordings. These officers are masterful at distinguishing accents and identifying what kind of room a speaker is in-things normal listeners can hear but do not attend to.

I cleared my throat, probably in an Alexandra-typical way, and, telling Gordon something she likely knew, announced that we were at the corner. Gordon was already turning it. She began reminiscing about the building we were pa.s.sing. As a young girl, she lived in this same neighborhood, less than a block away. "I remember when [the corner building] was being built." Her cane began tapping faster. "It has a gorgeous roof garden, overlooking the river." High above our heads, trees that would have been saplings when Gordon last saw them rustled and murmured.

A huge wind hit us as we turned the final corner back to her home. Gordon stopped in her tracks and stopped reminiscing. "That [wind] would be hard for the blind," she said, clearly thinking about "the blind" as though the category did not include her. The white noise of the breeze drowned out all the little sounds that are such a large part of Gordon's vision of her environment. But as she resumed walking, she continued to talk about her memory of the "new" building that had gone up on the corner. Gordon described the windows and the long, deep garden-and I gazed right at it, into her memory.

In front of her building she turned to shake my hand. "Nice to see you," she said. And then, as if noticing my smile in response, she added: "There's someone in my building who asked me, 'How come you use that word, "see?" How can you say "I see it"?' Well, I do see it. I said, 'see' has many definitions."

1 In normal conversation people gaze at each other only about a third of the time, with the listener looking at the speaker about twice as much as the reverse. When speaking, we mostly look not at the person we are talking to, but anywhere else-up to the sky, at our hands, out toward an indefinite segment of air. Many utterances begin with a brief look, then a turn away. (If you are speaking and you want a moment to hold someone's attention before they blast in with their thoughts, look away. Your eyes are signaling that you have got the floor.) We can pa.s.s the conversational baton with gaze, too, by turning and looking at our partner in conversation when we are finished speaking. Just by using eye contact, it is taught in improvisational theater, you can wordlessly establish a relationship between two actors, marking higher status or dominance, for instance, by holding eye contact while speaking.

2 All else is never exactly equal: even the same genome will be expressed differently given the slightest difference in environmental exposure, which every twin has from the time he is in the womb.

3This is especially so along Manhattan's westerly edge, as much of the country's weather pattern flows west to east.

"Sound comes to us; noise we come upon."

(Hillel Schwartz).

The Sound of Parallel Parking.

". . . the only sound was the hum of air conditioners . . ."

What was the first sound heard? The Canadian composer R. Murray Schafer, who wrote about the natural soundscape, answered his own question: It was the caress of the waters. As a species, our ancestors rose from the seas. We developed ears even earlier than we developed the ability to breathe on land. As individuals, the first sound heard by each one of us was watery again: we all began hearing the world filtered through the splashes of amniotic fluids. A fetus twenty weeks grown in her mother's belly has only enough sensory equipment to hear relatively low-frequency sounds, around 500 Hz or below.1 It is speculated that the developing ear, with its first few nerve fibers grown, can fire only up to a few hundred impulses per second, so that defines what the growing baby hears (not a lot). Still, it is enough to capture her mother's voice, important for her survival and development, as well as the sounds of the placenta, the gurgle of intestines, and the coursing of Mama's blood around the womb. Later in the fetus's development, more nerve cells will begin to fire together at rates representing a wide variety of frequencies, from 20 to 20,000 Hz. Before birth, as well as after, these young ears will hear sounds from speech to birdsong, from the rumble of distant thunder to the high hum of fluorescent lights.

As I headed out onto the street with Scott Lehrer, a sound designer for theater and a sound engineer for everything from vocal recordings to museum installations, the first sound heard was a bus idling loudly by the curb. This was not entirely unexpected. We were in the city, after all, and any urban dweller grows accustomed to being barraged by an unwelcome clamor. In this case, the sound seemed designed for our consideration. Which is not to say well designed. The engine made a bubbling, roiling sound-noisy, slightly interfering with sidewalk conversation. We would be happy when it, or we, moved away: the c.u.mulative effect of the sound was to make me feel increasingly uneasy. I wondered aloud if anyone could think of a way to like that sound.

Lehrer could.

"If you were just listening to it for itself, it could be a soothing sound, I think: it's a steady-state sound. And actually, if I recorded that sound and brought it into the studio, dropping down the pitch four octaves, you'd end up having this deep low repet.i.tive sound, like a kettle drum."

The idle was just percussion, Lehrer was suggesting; just rhythm. Without knowing the sound came from a tourist bus; without seeing the bus's girth, overly large for a city street; without smelling the bus's diesel spewings, the bus sound was just a waveform moving through the air. At a "steady state," meaning the shape of the wave is somewhat predictable, constant-and made up of low frequencies, below 500 Hz. In other words, it was. .h.i.tting us with tennis-ball-sized packages of air pressure at a rate of a couple of hundred a second. "Constancy" distinguishes it from the varied, changeable sounds that usually attract our attention. And it was a loud sound, but not overly so in a city full of sounds.

I welcomed the idling sound-ballthrowing bus because today we were walking to hear what we could hear. My time with Arlene Gordon had gotten me interested in listening. Most of my walks had focused on attending to the blocks visually. While some sounds have slipped through to my attention, I was struck by how unimodal I had become, trolling for the new thing to see and ignoring anything that I could not detect with my eyes (or nose). The human ear is open all the time; it has no lid to naturally refresh the auditory scene. Even holding our hands over our ears in the way children do, elbows akimbo and face a-grimace, many sounds get in. But while our ears are always open, we only half attend to sounds they carry, given the racket coming from within our own heads.

To walk and listen. To some extent, this would be an exercise in paying close enough attention to name what we hear. Simply giving a name to a sound can change the experience of it: when we see the thing that clatters or moans or sighs, we hear it differently. Naming, though, is not the exclusive reason for listening. Indeed, at times naming a sound aborts the experience of hearing altogether, shutting us off from continued listening and exploring the nature of the sound. Oh, that's just a downy woodp.e.c.k.e.r rat-a-tat-tatting. (Now we can move on.) Satisfied with our identification, we shift from attending to the downy ruckus to ruminating on dinner plans. So, too, goes the safari phenomenon: looking out over a savanna, patient observers will finally see a majestic creature appearing . . . then another . . . then a herd. The first thing we tend to ask is, what is that? To identify it-to name it-gets us no closer to understanding the creatures we have spotted, but it is often taken as a stand-in for that understanding. So named, the animals move on, and we move on to the next animal on our lists.

To be sure, it is difficult to describe a sound without invoking its name or source. "What's that funny sound?" my young son asks me about almost everything. I tell him, "It's a jackhammer," or "It's coming from that pipe." I default to an answer about the content of the sound. But another answer might be, "It's a wocka-wocka-rattle-tattle" or "It's a fffssssttttsss." With his unbiased ear and lack of vocal inhibition, my son will blow and toot a surprisingly accurate echo of what we are hearing. I am hopelessly bad at mimicking sounds with my own voice. I suspect my son will soon be just as bad: rare is the children's book that does not teach him that the dog says bow wow and the pig oink oink. This does not resemble what comes out of any dog or pig I know.2 So on this walk with Lehrer I was also aiming to listen to the sounds in and of themselves, to hear beyond their names. This is easiest to do as a tourist in a new environment, when even ordinary sounds are slightly off: the siren screams in discrete descending tones (as in the UK) rather than rending the air with a continuous ascending and descending peal (as in the United States); the telephone rings with a different ring. In an old city, a tourist hears the rumble of wheels over cobblestones that the native does not and notices sound bouncing differently between walls more tightly constructed than in s.p.a.cious American cities.

I met Lehrer while he was working, on a.s.signment tracking a sound. In a creative turn, he was looking for the sound in a palace of visual art: the Metropolitan Museum of Art, on the Upper East Side. His project was to find a sound to fit into a doc.u.mentary film about a museum show in Vancouver. As he described it, one sequence taken of the museum's atrium was unaccompanied by realistic "museum atrium" sound. Lehrer was now in search of that sound, based on an appreciation of what the atrium should sound like, given its size, height of ceilings, construction of floors, and density of structures and persons. I shadowed him as he moved through the Met, quickly scanning each room before judging it useless-a central room that served as pa.s.sage to other exhibits was "too busy"; a fountain in a large, atrium-like room was disqualified because "the water is pretty specific"-or promising. In the latter cases, after surveying the scene, Lehrer stood out of the way, spoke a description of the room into a small audio recorder, and then stood quietly recording the room. To all who pa.s.sed he would have looked like a man in reverential contemplation of a distant sculpture.

When Lehrer had gathered an audio-recorderful of atrium sounds, we left the museum. That was when we encountered the bus. We crossed the avenue and left it behind. On a side street on the Upper East Side, we were wrapped in relative quiet surprisingly quickly. It was an early spring day, and the streets were full of the humanity that emerges after a winter's sleep. But in this part of the city the humanity is remarkably peaceable and hushed. I worried that we would only hear the rustle of expensive silk undergarments from this neighborhood.

The morning had seen rain but the afternoon had forgotten it. Trees were in hopeful bloom; children ran up and down the steps in front of the museum. Their gleeful shouts grew faint. We heard birds cheeping above our heads; our footsteps were again audible. Lehrer paused and looked back out at the street. "It's dry now, but did you hear the sound of the tires earlier?"

I had not.

"Tires actually stick to the pavement more because of the water" when it rains, he said. "You can actually hear the sound of rubber on water; it's different than rubber on pavement."

I felt for a moment like someone who just discovered she had ears. How had I never heard this sound? It was not just the sound of water splashing; it was not just the sound of wetness; it was the sound of tire rolling over water. I had not heard it! A barreling taxi, its tires probably making the regular old rubber-on-pavement sound, broke through my reverie as its driver rode his horn. Another car horn responded with equal outrage. I smiled: there was the noisy city I knew.

Utter noise: this is the familiar acoustic impression left by a city. Even standing side-by-side, two city dwellers attempting conversation must make an effort to be heard; a mumble would disappear into a pa.s.sing truck's braking sigh, or the white noise of street traffic. The landscape of the city is filled with broadband sound drawing from a wide range of frequencies. While we may be able to attend to particular sounds, our experience is of a clamorous, unintelligible din-what has been called a lo-fi soundscape.

What makes that "noise" and not just neutral "sound" is another question. The avant-garde composer John Cage famously declared that "music is sounds," and thus appropriated ordinary sounds to be his music. In one of his compositions, the orchestra is silent for four minutes and thirty-three seconds; whatever sounds come in through the window of the concert hall or emerge from the increasingly restless and puzzled audience const.i.tute his music. Still, if Cage was right, it need not follow that all sounds are music(al). Any sound we do not like we call noise, thereby introducing a subjective a.s.sessment to the din. That subjectivity is always there in talking about noise. Despite the precision of his science, the early physiologist Hermann von Helmholtz characterized "noises" as sounds "tumbled about in confusion," bothering mind and matter alike. Others invoke simply "interruptedness" as the character feature that makes a sound into noise.

The relativity of noise is rea.s.suring to me. It seems more likely I could find something charming in the soundscape of the city if its noisiness depends as much on my psychology as on the sounds themselves. It is certainly the case, for instance, that one's experience of urban sounds changes with exposure. To the visitor, the city is just noisy; over time, one does not hear less, but one may attend to the details of it less.3 There is one sound that city dwellers seem to agree on as noisy, though. Lehrer and I did not have to wait long for it to come to us. As we walked along the quiet side street, the ultimate in interruptedness, a motorcycle with souped-up exhaust pipes came racing down the avenue we had just crossed. It might have been in our sights for two seconds at most, but the disruption was enormous. We had to stop talking. People walking by us stopped talking. I could almost swear that the birds stopped their chirping, the buses their rumbly idling, and our footsteps their echoing.

Some of the motorcycle's noise is just its loudness, clearly: less than a half block from the cycle, we were probably hit with 100 decibels or more. Decibels are the subjective experience of the intensity of a sound.4 Zero decibels marks the threshold for hearing a sound-and in a modern city, there is never a moment of zero decibel silence. We mostly reside in the 6080 decibel range, which includes sounds from normal conversation across the dinner table, vacuum cleaners, and traffic noise. Once a sound gets to 85 decibels, it begins to damage the mechanism of our ears irreparably. The reason lies in the mechanism itself.

Cilia, tiny hair cells that stand upright in the cochlea, sway and jiggle when the vibration of air-the rush of air that is sound-wends its way into the inner ear. So stimulated, the cilia trigger nerves to fire, translating that vibration into electrical signals that give us the experience of hearing something. If those vibrations are strong enough, the hair cells bend deeply under their force. Air pressure can mow, crush, or sever the hairs until they are splayed, fused, floppy, or fractured-an earful of well-trodden gra.s.s. Bent and damaged enough because of exposure to loud sounds for prolonged periods, the hair cells do not grow back; the ears lose their neural downiness. The world becomes progressively quieter for the person attached to those ears, until there are no sounds, no music, no noise.

Cities are crowded with sources of sound regularly approaching this threshold of hearing loss. There are biological reasons for why we are so afflicted: our ears are designed to let in the frequencies at which we speak-from a few hundred to a few thousand hertz. Enormous numbers of man-made sounds occur in those same frequencies. We often find high pure tones the most irritating: the screech of a subway turning a tight corner or braking, at 3,000 or 4,000 hertz, or the sound of fingernails on a chalkboard, between 2,000 and 4,000 hertz. These sounds clobber us because of the shape of the human ear, which allows high frequencies to find their way efficiently to the cochlea. The very design of the ear amplifies these vibrations for waiting hair cells. But it is not just our ears that find the sound distressing; it is our brains. If we know that we are hearing what we have already deemed an "annoying sound," our bodies react to it as though it is: we have a sympathetic nervous system response, usually reserved for final exams, suddenly appearing lions, and the sight of our beloved. We sweat, and then we notice that we are sweating, and we sweat some more.

As Lehrer and I walked down the street in the wake of the motorcycle's roar, I noticed myself curling my hair around my left ear to expose it for better listening to what he had to say. This was perfunctory: our hearing is exceedingly sensitive, whether covered with uncurled hair or not. As Lehrer spoke, sound energy was heading down the winding caverns of my outer ear and being conducted through slender bones, making a membrane vibrate and those tiny hair cells dance. The force required to move our dancing ear hairs is so minimal that it would disrupt the tiniest mosquito not at all.

Unlike our other senses, in listening, the normally functioning ear actually makes its own noise, something called otoacoustic emissions. Though we do not generally hear these sounds ourselves, they are suggested to be sufficiently distinctive that they could be used as aural signatures to identify individuals. I inclined slightly toward Lehrer and listened for his. Nothing. Instead, a familiar sound, that of a compact, dense object making quick contact with a softer solid ma.s.s-thwack!-banged in our ca.n.a.ls.

We both turned to our right, detecting the direction of the sound at once, coming from beyond a chain-link fence. A boy was throwing a softball with an older man in a mostly empty schoolyard. Water puddled along the corners of a basketball court; a set of bleachers sat unused. I reflexively grabbed the chain-link as though it would help me hear better while I peered through it. Sounds of a school playground: is there anything more evocative of childhood? The bounce of different kinds of b.a.l.l.s on the court or in hand, the shrill cries of children hopping or running or dodging one another or in hot pursuit, the slap of a jump rope on asphalt, the rattle of a ball off a backboard. In the corner of the yard was a set of playground equipment and, whether I saw them or not, I thought of swings-impossibly squeaky swings, standard-issue rubber seats, bowed by the heavy bodies of children, tracing wide arcs. I have not only sat in uncountable swings, but I now sit my son in the city's playground swings on a regular basis, controlling the pace of the squeaking by pushing him faster or slower.

Just seeing the playground called forth a memory (my own son swinging) and evoked a clear feeling (how magnificent this little boy is) that nearly replaced my perception of the sight and sounds right in front of me. Awakened was the memory of the weight of his body as I pushed him, of looking at his cold hands gripping the chain in winter, of wondering how high is too high; and even of my own childhood, wondering what it would be like to jump off a swing and then, one day, after watching other kids do it hundreds of times, letting go, feeling the slice of s.p.a.ce that formed between me and the seat, and then falling. It was nothing like my antic.i.p.ation. It was like being lifted up by a benevolent soft hand.

I closed my eyes and half-shook my head to return to the present. To pay attention to one's sound memories is to open the door to a closet bursting at the hinges: something is stuffed just inside, on the edge of falling out and into your consciousness. In the present, Lehrer was talking. And I quickly returned my focus to his voice, for he was talking about squeaking sneakers.

"That is one of the keynote sounds of the schoolyard," he said, referring to Schafer's idea of those elements of a soundscape that may not be consciously attended to but are characteristic of a s.p.a.ce. The ball-tossing boy was wearing orange high-tops, and I tried to match his foot movements to the squeaking I was hearing. It was a basketbally sound. So basketbally, in fact, Lehrer said, that televised pro basketball places microphones on the court itself to pick up the sound of the squeaks. "They know that's an exciting sound, hearing all those basketball sneakers maneuvering." The rambunction!

I wondered if the engineers ever ramped up the sound for greater effect.

"Oh, absolutely!" said the sound engineer.

We lingered a while by the schoolyard. Two teenage boys entered from stage right and headed for the basketball court stage left. One leapt up, his hand extended for the rim, the other added the tw.a.n.g of a dribbled basketball to the s.p.a.ce. It hit us like the smell of a ripe melon in our faces. I asked Lehrer why the sounds were so crisp and ringing here. It would not be a good place to hold a chamber music concert, but it was full of bright, loud sounds.

"It's all pretty simple physics," he claimed. All sound travels at the same speed, around eleven hundred feet per second. So if one takes into account the distance from the sound source to the surrounding surfaces, and looks at what those surfaces are made of, the result is a decent approximation of what the listener will experience. In this s.p.a.ce, with three brick walls and an asphalt surface underfoot, "It's very reverberant." The softball t.o.s.s.e.rs were close to the back wall; the basketballers were near a side wall. Their proximity to the walls reinforced the sounds they were making. "If you listen," Lehrer said, "you can hear the early echoes, when the sound really snaps. . . . You won't hear the echo off that [first] wall as being a separate sound; it just reinforces the original sound, making it sound louder." For the other walls, another eighty feet away, we estimated, it would take seventy milliseconds for the sound to reach it and come back to our ears, making a second sound-"which is perceptible: it sounds like TIH-ka."

The reason we could not distinguish the sounds of the basketball or the softball from their first, early echoes is that the near walls were less than twenty or so feet away. The human ear does not have the acuity to distinguish similar sounds made less than forty milliseconds-less than 1/20th of a second-apart. The sounds blur together, making a single larger sound cloud. Lehrer takes advantage of this auditory phenomenon in his live-sound work when he needs to control the "articulation" or the intelligibility of the sound system: if he uses a speaker in a theater to amplify the sound from the stage, it had better be set up so that the audience hears the sound from the speaker synchronized with the sound onstage. Given the way our ears work, though, there is room for error-about forty (or less) milliseconds' worth-which means that a speaker can be set about fifty feet away and few people will hear the sound as echoing.

The amount of reverberation of sound in a s.p.a.ce like this schoolyard is what Lehrer called the "wetness" of the s.p.a.ce. This s.p.a.ce was pretty wet. (And full of puddles, too, by coincidence.) Wetness is something a sound engineer can manipulate in a recording, turning it up or down for effect. Deep inside the museum a half an hour earlier we had walked through small rooms with carpets on the floors and weavings on the walls: these were "dry" rooms. The driest rooms are studios, acoustically "dead" rooms with minimal reverberation, which allows the sound mixer to control the sound effects himself, rather than leaving it to the room to define the sound. The wetness of a room, and the kinds of early reflections and echoes one hears, are, Lehrer said, "what makes rooms sound like 'rooms' to us-why a bathroom sounds different from a living room, sounds different than the kitchen." It has to do with the size of the s.p.a.ce, the distance to the walls, the objects within, and the surfaces of those objects.

Despite my familiarity with rooms, this was a kind of noise I had never listened for. Nonetheless, I could at once a.s.sent that yes, it seemed likely there was a definitive bathroomlike sound-hence, all the singing that goes on in bathrooms but not in dining rooms. Of course, we do think about these sounds when they are dissonant with what we see. Should a kitchen scene in a movie have a "bathroom sound" to it, the audience might notice something is off. Sound engineers compile and keep catalogs of specific room sounds, each with the right set of reflections and reverberations and frequency content. "I have my 'bathroom preset,' " Lehrer said, "and we plant the actor's voice"-recorded not in the bathroom but in a dry room in a studio somewhere-"into that reverb unit. What comes back is something that gives you the sense that the person is in the bathroom."

I vowed to listen for my office sound when I returned home. I wondered if it made a sound without me in it.

Lehrer and I reluctantly turned from the schoolyard and headed down the street. Pa.s.sing under a low scaffolding, I remembered Gordon hearing the sound of the enlarged awning with her probing cane. Lehrer heard the change, too. We paused and smiled with the a.s.sumption of shared recognition at a clutch of tourists walking in the other direction. They did not appear to understand why these crazy people were giddy at the scaffolding. As we approached an avenue, the air became thicker with sounds: people moving and chattering, birds overhead, eighteen-wheelers and buses roaring downtown. A metal pipe dropped somewhere and banged three bangs before settling.

Among the rumbles and crashes, crowd noises and traffic, I felt impressed that I could hear and understand every word that Lehrer was saying-and he, I. Psychological science names this the "c.o.c.ktail party" effect: the ability, demonstrated most characteristically when at a noisy party, to distinguish what the attractive person in front of you is saying from the general din of the room. We do this terrifically well, as a species. Even better, if someone three conversations to our right happens to mention something of interest to us-such as our name, or the name of someone we know-we are often able to tune right over to that conversation, like a perfectly smooth radio dial.

How we do this is still somewhat of a mystery, but one clue comes from "auditory restoration," or, less jargonly, perceptual filling-in. You have almost certainly experienced this phenomenon without knowing it. When you are listening to, say, a friend talking, it is rarely in a perfectly quiet environment. Regularly, other sounds are louder than and intrude on the speech sounds coming out of your friend's mouth. We only notice this when the noises drown out all speech; most of the time, noise might mask what the person is saying, but we do not miss a beat. Our brains spontaneously fill in the gap, constructing the sound that was missed. We do not even have the experience of missing it, so smooth is the filling-in.

If you are skeptical, consider the visual blind spot, which prompts the visual a.n.a.logue of our auditory restorative process. By "blind spot," I do not mean the metaphoric blind spots we all have for the elephants right in front of us. I mean the hole in our visual field created by the anatomy of the eye. The retina, at the back of the eye, is slathered with photoreceptors that convert light to electrical signals. There are so many that any light that hits our eyes will inevitably hit one of these receptor sites; with our eyes open and daytime in front of us, we spontaneously and immediately create an image of a full, dynamic visual scene. But. Just one thing. Right in the middle of the retina there is a small hole. In a strange design twist, this hole is the necessary exit route for the nerve cells from the eye: the tunnel through which the optic nerve, ushering all the visual information that has. .h.i.t the retina into the brain, leaves the eye. Where there is a hole, though, to let the wiring through, there are no receptors. So any light that hits that part of the retina is not noticed by our eyes or our brains. We should see a small black hole in front of us every time we open our eyes. We do not see that hole, however, because our brains, clever tissues, swoop in to pick up the slack. Our brains fill in the hole with what it expects to be there. We are constantly, fluidly making up what we see.

Given our ability to "see" things our eyes do not see, it should not be surprising that we "hear" things our ears do not hear. Still, this feat of auditory filling and sorting is nothing compared to that accomplished by other animals. Take bats. For most species of bats, which, though not blind, evolved to navigate by echolocating, tuning in to a conversation on a noisy street would be child's play. Echolocating bats see the world by hearing it, and they hear it by emitting high-frequency calls from their nose or mouth and then listening for the sounds to bounce back to them, all while maneuvering at high speeds. The intensity and the speed at which the sounds come back allow bats to construct a picture of their environment on the fly. Their sound vision is acute: it enables them to catch their prey-usually insects themselves working hard to avoid detection-on the wing.5 It allows them to distinguish soft objects from hard; note whether an object is far, near, or very near; even distinguish between types of trees. New York City's little brown bats must successfully discriminate the broad-leafed London plane from the maples and oaks. Even more incredibly, all this parsing and organizing of the sounds of the world happens while dodging branches and swooping in on prey. Bats need to adjust their picture of their environment as they move, and they do this by instantaneously changing the rate, pitch, and loudness of their calls according to what they are hearing. Then they are faced with a further challenge: as social animals, bats are always around other bats-all calling and flying themselves. Sometimes thousands of them flit about together in a small s.p.a.ce. How they distinguish the sounds of other bats calling from their own echoes, and from the warnings and solicitations that are a normal part of bats' communication with one another, still puzzles researchers. It does appear that once in a while their strategy is just to go quiet.

Lehrer and I took that approach for a moment, too. We paused at the next corner and stopped talking, better to listen.

Our ears were alert to every sound. Cars came and went; pedestrians arrived and retreated. I collected these sounds like beach pebbles, warmed in my hands and pocketed. The jangle of a dog's tags; the sc.r.a.pe of his toenails on concrete; the leaked trickle of music from between a pa.s.serby's earbuds and her ears; the rumble of a subway underfoot. Trucks roared by; buses whined. In the lull between the pulses of vehicles, birds tweeted over one another in short sharp descending tones. Then a small sound drama: a man in a jumpsuit dragged a heavy vinyl bag up onto the curb in front of us; the weight of the bag could be seen in the man's cant and heard in its low rasp on the sidewalk. A moment later, an empty mover's dolly was rolled by, attempting to catch up with the jumpsuit. It nearly swiped a third man sweeping trash into a plastic dustpan, which folded up with a thwack.

Lehrer looked pleased. "A lot of stuff just happened sonically! Think of all the elements going on in those little events," he said, motioning at the s.p.a.ce where the dragger, dolly, and sweeper had pa.s.sed. "It was a symphony!"

Out of nothing, a symphony. As someone subjected to the noise of the city day and night, I was getting the sense that Lehrer's ability to turn bag-dragging into symphony was a shrewd adaptation. I was witnessing his psychological ability to turn the same noise I heard into music. Surely it is not only Cage who has a monopoly on this kind of transmogrification. Should we be able to do so on command, we would certainly be the better for it. We have not just emotional reactions to music, but physical reactions to sound. In Homer's telling, choral singing kept the plague at bay. Roman writers claimed that a short flute piece could relieve gout discomfort. And David's harp was famously used to loosen the grip of King Saul's mental illness. For myself, just a few chords played by Art Tatum will calm me right down. Of natural sounds, those that are "self-similar" are more likable: the sound of water running; the susurration of a breeze in the canopy of a tree. These sounds share something with fractals: we hear them as the same when played at different speeds or different loudnesses. Something about them resonates deeply in us.

Our intersection was providing the typical voices of the city environment, with its trucks and buses, street preachers and loud talkers, high heels and ring tones. At times, people have tried to make inventories of all the noises of the city-a taxonomy of the bright or dull, simple or complex, brief or enduring sounds that fall around them on waiting ears. It seems an impossible task. We do not have enough attention to notice every sound, or words with which to mark them. Even the buzz of our own bodies working-the thrumming of our hearts, the click of our joints-eludes our attention. To hear this, we need to go into an anechoic chamber. In these strange s.p.a.ces, all external sound is muted. One can hear only the swoosh of blood circulating, the lapping click of the heartbeat, and the muscles of the lungs stretching with each inhalation.

In the city, residents become inadvertent experts on urban sounds. I know the difference, I realized, between the sound made by a shuttle bus and a city bus; I can recognize the acoustic signature of alternate-side-of-the-street parking days; I can tell from the language spoken around me whether I am on Broadway or a block away, on Amsterdam Avenue. Those who regularly walk in the forest may come to know each tree by its characteristic sound, be it a sob and moan (fir), whistle (holly), hiss (ash), or rustle (beech). In the forest, my ears are blunt instruments. In the city, they are well tuned. Sure, in the country one might be able to count the number of cricket chirps in order to determine the temperature outside.6 But in the city, I know within seconds of waking up whether it is a weekday or a weekend by the sounds of the street alone. If a garbage truck is groaning, weekday; if the distant sounds of the highway are turned down a notch, weekend.

At our corner, a car backed slowly into a parking spot parallel to the curb. Its tire, turning, caught the edge of the sidewalk. A splendid rubbing-squealing-yawning-pull of rubber fibers and concrete filled my ears. This was a sound not just of a city but also of a particular moment in this city's life. The sound of parallel parking, of cars fitting into a crowded s.p.a.ce, of two synthetic objects struggling to keep their integrity-this noise may disappear from the city in time. Either the design of urban environments, the rules of parking, the mode of transport, or the material of tires or sidewalks will change enough so that at some point the sound becomes rare. Then, if it is lucky, it will live on as a sound effect in period movies about the early twenty-first century, added to the pages of the Catalog of Lost Sounds among the rings of telephones and cash registers, the m.u.f.fled flash-powder burst of an old camera, and the catch of the latch of an ancient refrigerator door as it closes.

Lehrer was speaking. "You feel it?" he asked. Under our feet, a train rumbled again. I could hear the subway, if I listened for it, but the sound was low enough that we felt it more than heard it. "Sound is a physical thing, you know-you reach a certain low frequency where you actually start feeling sound as well as hearing it. We can feel that bus." He nodded over to a bus cruising down the street. "That bus is shaking us."

It was true! A large tour bus ripped the air with the sound of its engine and the press of its tires, but I was surprised to find that it also jostled us with bursts of air. Lehrer pointed out another sound: Ka-PLUMP! A car struck a manhole cover ill-placed over its hole in the street; again, we heard it, but I also felt it. There is a tactile side to sound. More so than with vision, we can experience the physical agent (sound waves) in two ways at once. Once light becomes "ultraviolet" and invisible to us, we can feel it, but it is the feeling of our tissues slowly burning.7 With sound, the overlap is less painful and more common: in low frequencies, the sense of hearing morphs into the sense of touch. The subway's rumble was almost tangible in the soles of our feet and our stomachs.

This fact has been used to great effect in insidious ways. In some cities, police sirens have been changed from their familiar-and ignorable-lullaby to a low-frequency ba.s.s boom that can be felt in your body almost before your ears. Audible sounds have been used in warfare: the U.S. government currently uses a so-called non-lethal acoustical device, which sends out low-frequency sounds in a very specific range to control crowds or as a warning.

There are other cross-modal components to listening. It is visual, for one thing. Close your eyes, and your hearing is more focused. This is not because we need to shut off one sense in order to use the other. On the contrary, vision changes hearing. Though we hear with our ears, we often turn our heads to confirm with our eyes what the sound is. This practice seems ridiculous-who listens with her eyes?-except that it is so sensible. Straining to hear the person you are talking to on a subway platform, you would do just as well to stare intently at his mouth as you would to turn your ear toward him. Seeing what he is saying-through reading lips and monitoring expression-is sometimes as good as actually hearing it. Should you feel unpracticed at this skill, think again. You have been watching people speak all your life, and unconsciously training yourself to hear visually. Similarly, we may only be satisfied with our guess at the source of a sound after finding it with our eyes. The strident car alarm heard out your apartment window changes character when you discover which car is spouting it (and it thereby becomes more hectoring, usually).

Movie makers take advantage of our hearing with our eyes, Lehrer told me. In capturing a street scene like one we were gazing at, the foleys, in charge of sound, do not try to record it all. Instead, "they look for someone that people might want to visually focus on"-and capture the sounds, say, of just that one person's footsteps.

"And we can't hear the other people?"

"No."

"You don't have to get the other people?" I was impressed.

"Not really. You should watch that sometime on a film and see how often you see three or four people walking and you only hear one person's footsteps."

The sound has created a visual focus, and it is untroubling that we cannot hear the rest. I remembered the mute pigeons from my walk with John Hadidian; in their quietness, the birds now seemed suited to film. It changed my perception to imagine the noise we were hearing as in some way cinematic. The introduction of sound to films swung the expressive emphasis from what was seen to what was heard. Sure, film is a visual experience, but sound is used dramatically and effectively to heighten that experience. And at times, sounds can allow us to see something that is not even there. A dog barking off-screen is enough to invoke the image of a fenced-in, menacing guard dog, a stranger pa.s.sing by, or an unseen intruder or disturbance. Viewers of science-fiction films know that automatic doors make a satisfying pssht sound, so directors can take advantage of its familiarity: to show a door opening, one need only film static shots of a door closed and opened, and overlay them later with the added sound effect.

Of course, one of the things that is not sound tracklike about the sounds of the city is that the heard sounds are all functional, not emotional. Rather than inflecting what is happening with swooning violins, or punctuating a scene with comic, melodramatic, or rhythmic sounds, we just hear the sounds things make and the noises people utter. Our steps are rarely synchronized with a beat, or our emotions with a tune.

What would it be like to walk through a city with your own expressive sound track, in which a mugger arrives with menacing music, or the sight of a loved one is decorated with a swell of violins? I suspect this is one of the pleasures of walking while listening to music through headphones, or with earbuds burrowed into the inner ear. Certainly the activity distracts the walker enough from the actual experience of being on the street that he can become an annoyance to others, as his social sense is reduced to almost nothing, much like Fred Kent's cell-phone talkers. Others become merely characters in the great movie unfolding in three dimensions to the sound track coming through his earbuds. He moves through the film weightlessly, undisturbed, with n.o.body breathing down his neck and interrupting his flow. He stops experiencing what is actually happening outside; he is merely an observer, watching it happen, even while moving through it. It is almost as if, if he reached out to touch the person walking astride him, his hand would fall through their arm, it being but an illusion projected on the mesmerizing screen of his creation.

From our corner we were treated to a spitter's throat-clearing, mouth-contorting expurgation, so phlegmy we reflexively recoiled even at our safe distance-as though we were at risk of tasting it ourselves. Hearing can invoke memories that are emotional-as the nostalgia of the swings-or visual or tactile. To hear a regular, tonal beeping in the city is to imagine a truck's rear lights on and to nearly picture it creeping backward. Much of what I was finding to be distinctive about the sounds on this urban walk was the non-sound sight or feeling a.s.sociated with them: the back strain felt in the man struggling with his dragged load; the feeling of popped gum in my mouth and on my lips on hearing a girl casually snap her gum as she pa.s.sed.

The ears feel connected to the entire body. Music taps our fingers and feet and, if we are so inclined, our hips. The pleasure of a lover's voice is felt in our viscera and stands the hairs of our neck's nape on end. Or, as on this walk, we can feel nostalgic, empathetic, disgusted, or exhausted by what we hear. Hamlet's father was killed by the herb henbane poured into his ear-and no wonder, because the ear was thought to connect to all internal points, to course "swift as quicksilver . . . through / The natural gates and alleys of the body." Even the sound of the click of heels from a woman walking by felt empathically translated into myself, and I could feel what it is like to teeter on those high-heeled perches.

Daily, we are exposed to sounds that affect our bodies in ways we might not know. Low-frequency sounds are the source: waves coming too infrequently for our ears to make much of them but slipping into us quicksilver-like. Low enough, and we call it infrasound, as though if humans cannot hear it, it is not a true sound. Of course there are plenty of familiar animals who make a living using infrasounds-elephants, for instance. A bull might stomp a message that travels ten kilometers along the ground, as infrasounds are resilient to weakening as they travel over s.p.a.ce and time. Lots of man-made objects inadvertently produce infrasound. These noises are omnipresent and damaging.

Ventilation fans moving stale air out of large office buildings, thrumming along at a few hertz, are doing a service, but they have also been implicated in thrombosis. Their low-note hums not only get into our bodies' gates and alleys but also might vibrate in rhythm with the heart, amplifying and thus disturbing normal circulation of blood. Sounds traveling at 7 hertz, including wind sounds, have been implicated in headaches and nausea, as they vibrate in time with the alpha waves of the brain. Loud sounds can cause the heart to seize or skip a beat. For whales, Navy sonar signals interrupt their communication and damage the tissue of their ears.