On any given day, millions of conversations reverberate through New York City. Poke your head out a window overlooking a busy street and you will hear them: all those overlapping sentences, only half-intelligible, forming a dense acoustic mesh through which escapes an exclamation, a buoyant laugh, a child's shrill cry now and then. Every spoken consonant and vowel begins as an internal impulse. Electrical signals crackle along branching neurons in brain regions specialized for language and movement; further pulses spread across facial nerves, surge toward the throat and chest and zip down the spine. The diaphragm contracts—pulling air into the lungs—and relaxes, pushing air into that birdcage of calcium and cartilage—the larynx—within which wings of tissue draw near one another and hum. As this vibrating air enters the mouth, the tongue guides its flow and the lips give each breath a final shape and sound. Liberated syllables travel between one person and another in waves of colliding air molecules.

All these conversations are matched in number and complexity by much more elusive discourses. The human brain loves soliloquy. Even when speaking with others—and especially when alone—we continually talk to ourselves in our heads. Such speech does not require the bellows in the chest, quivering flaps of tissue in the throat or a nimble tongue; it does not need to disturb even one hair cell in our ears, nor a single particle of air. We can speak to ourselves without making a sound. Stick your head out that same window above the crowded street and you will hear nothing of what people are saying to themselves privately. All that inner dialogue remains submerged beneath the ocean of human speech, like a novel written in invisible ink behind the text of another book.

Some people have tried to eavesdrop on the silent conversations in other people's minds. Psychologists have attempted to capture what they call self-talk or inner speech in the moment, asking people to stop what they are doing and write down their thoughts at random points in time. Others have relied on surveys or diaries. Andrew Irving, an anthropologist at the University of Manchester, decided to try something a little different: a peripatetic transcription of consciousness.

While completing his PhD in the 1990s, Irving became interested in how people's thoughts, especially their perception of time, change as they approach death. He gave volunteers with serious or terminal illnesses voice recorders and asked them to walk around their neighborhoods, speaking their thoughts out loud. In effect, he turned each of his volunteers into an amanuensis of his or her own chattering mind. "I realized that you could see somebody sitting in a chair or walking along the street and it may seem like nothing much is happening—but actually an incredible amount is happening," Irving says. "In their heads they may be going from childhood to religion to questioning God to trying to imagining what exists beyond death."

More recently, Irving received a grant to track down these volunteers and find out what happened to them. As a side project, he decided to record the inner dialogues of people walking in New York City—to map part of the city's thoughtscape, layered beneath its audible soundscape. He approached strangers at different points in the city. "Excuse me," he would say, "this might sound like a strange question, but can I ask you what you were thinking before I stopped you?" If the stranger did not run away, he would ask them to wear a microphone headset attached to a digital recorder and speak aloud their thoughts as he followed closely behind with a camera. He would not be able to hear what they were saying, Irving explained, and they would be free to walk wherever they liked and continue their business as usual.

"I was surprised by how many said Yes," Irving says—about 100 in all. By overlaying the recorded audio onto the videos, he has created portraits of individual consciousnesses on a particular day in New York City—transcripts of people's inner dialogues that remind one of works by Virginia Woolf, James Joyce and other writers who were especially interested in recreating the mind on the page. He calls the project "New York Stories: The Lives of Other Citizens." Different videos focus on different parts of the city, such as streets, bridges, squares and cafés.

https://vimeo.com/64922792

Irving's videos are simultaneously naturalistic and as objective as possible. In the lab, in front of a researcher, people are often reluctant to reveal exactly what they are thinking. Writing a diary of inner speech is somewhat more private, but many people find it annoying to regularly drop everything and make an entry; sometimes it's difficult to remember what one was thinking about even minutes earlier. In Irving's videos people are living their lives more or less as usual, walking and talking to themselves as though they were unaccompanied. Of course, people who are not completely comfortable with the scenario sometimes speak into the microphone as though trying to entertain someone else. And getting people's inner speech on tape captures only linguistic forms of thought, neglecting the kind of thinking that happens in images and scenes, for example. Still, Irving's videos are permanent records of fleeting thoughts, of dynamic mental processes unfurling in real time. They give us nearly direct access to a kind of internal communication we usually do not share with one another.

https://vimeo.com/64922800

In one video, a young woman named Meredith walks along Prince Street in downtown Manhattan. She briefly wonders if there's a Staples nearby before reminiscing about a recent visit to her friend Joan, whom, we learn, has cancer. Meredith contemplates her friend's situation for the next two minutes, tearing up at the thought of "New York without Joan." Abruptly, she notices a café where she used to sit and people watch, laments how it has changed and resumes her search for a Staples. Fewer than 30 seconds later, she is talking to herself about Joan again—but serious reflection on mortality is punctuated by more provincial thoughts about navigating the crowds. When she remembers how bluntly and simply Joan announced her cancer, Meredith begins to choke up—then interrupts herself with a little burst of frustration while crossing the street: "What is this craziness? Five cars in the middle." The segment ends with Meredith asking herself, once again, whether she is any closer to a Staples.

Meredith's meandering thoughts recall Clarissa Dalloway's roaming mind in Virginia Woolf's novel Mrs. Dalloway. As she walks the streets of London, Clarissa entertains an ephemeral memory of throwing a shilling into the Serpentine, before transitioning to a more somber meditation on death: "Did it matter then, she asked herself, walking towards Bond Street, did it matter that she must inevitably cease completely; all this must go on without her." Moments later she is commenting to herself on books in a shop window, then deriding her "pea-stick figure," then admiring a fishmonger. She converses with herself about war, immortality, past romances and what kind of flowers she should buy for her party.

https://vimeo.com/64922797

Woolf would likely have adored Irving's videos. She wanted to write about "an ordinary mind on an ordinary day." As opposed to many of her contemporaries, she was far more interested in what was happening inside people's heads—in thought, memory and consciousness—than in detailed descriptions of buildings, countenances and clothes. She wanted the reader to perceive almost everything through her characters' minds, rather than dictating a traditional plot with third-person narration. Like a telepathic moth, the narrator in Mrs. Dalloway flits from one person's consciousness to another as they go about their business in London. Though the characters do not know it, their minds ring with echoes of one another's inner speech: even when apart, they think of the same events at the same time—of Big Ben's gonging or a car backfiring like a pistol; they constantly think of each other and lose themselves in memories of shared experiences.

"There's always this assemblage of voices simultaneously going on in public all the time—but you can't hear it," Irving says. "I'm interested in whatever people are thinking about. 'What should I buy for dinner tonight? Should I buy pasta?' That's just as interesting to me as something more dramatic."

https://vimeo.com/64922801

Andrew Irving would like to acknowledge that his research was funded by the ESRC (UK) and Wenner Gren Foundation (New York)