From 1934 to 1970, Louie Mayer worked as a cook and housekeeper for writers Virginia and Leonard Woolf at their home in Rodmell, England. Her very first day on the job, she noticed something strange. As Louie worked in the kitchen, voices poured through the ceiling from the upstairs bathroom, where Virginia was soaking in the tub. "I could hear her talking to herself," Mayer recollected. "On and on she went, talk, talk, talk, asking questions and giving herself the answers. I thought there must be 2 or 3 people up there with her." Recognizing Louie's bewilderment, Leonard explained that Virginia was trying out sentences she had written the night before because "she needed to know if they sounded right."

For Woolf, prose that "sounded right" was often prose that sounded like thought. Verbal thought, specifically, or what psychologists call inner speech: all those self-addressed sentences spun silently in the mind throughout the day. In many of Woolf's novels—particularly Mrs. Dalloway, To the Lighthouse and The Waves—passage after passage reads like a transcription, or an eloquent translation, of her characters' inner soliloquies. Of course, none of us has direct access to anyone else's consciousness. To faithfully recreate the way people talk to themselves in their heads, Woolf examined her own mind and tried to catch herself in the act of soundless self-talk. In the process, she undoubtedly encountered a quandary that has frustrated novelists and psychologists alike: directing the spotlight of attention onto inner speech risks altering that speech. Such introspective analysis is like "trying to turn up the gas quickly enough to see how the darkness looks," wrote William James.

How, then, do we watch a silent sentence unfurl in the mind without changing it? We can't, says Russell Hurlburt, a psychologist at the University of Nevada, Las Vegas. But, like many writers and scientists, he has strategies for observing his subject with minimal disturbance. Hurlburt calls his technique Descriptive Experience Sampling and, when it comes to his subject of study, he prefers the more active term 'inner speaking' to 'inner speech.' He asks volunteers to carry a beeper that goes off randomly about six times a day. Whenever the device makes a noise, the volunteers must stop what they are doing and write down whatever they were experiencing in their minds the microsecond before the beep. Later, researchers interview their volunteers to learn more about each noted instance of mental activity.

Because this type of documentation relies on first-person reports that in turn depend on short-term and long-term memory—which are prone to error, bias and confabulation—it will rarely be as objective as, say, placing an inanimate voice recorder between two people having a conversation. But it brings people as close to observing their own inner speech without interfering as possible. It's like standing at the front of a cave and secretly recording the echoes of a very reclusive orchestra playing within; the music you hear is perhaps a little distorted, but it's the orchestra's music nonetheless.

Hurlburt and his colleagues have used Descriptive Experience Sampling to study inner speaking in a wide variety of people who presumably have mental habits that range from the typical to the unusual. Adolescents, college students, women with bulimia, people with depression and veterans with post-traumatic stress disorder, for example, have all participated. Here are six specific moments of inner speech rescued from the mind's caverns:

1. Angela was driving near campus and had just noticed for the first time a Thai restaurant. At the moment of the beep she was enthusiastically saying to herself, “Thai food!” This speaking was silent, in her inner voice that sounds just like her external voice, in an enthusiastic tone and inflection consistent with her welcomed restaurant discovery.

2. Brian was innerly speaking, “I don’t want to go,” saying this sentence a second time as he tried to figure out or rehearse what he might say to his friend who was going to call to ask him to hang out. “I don’t want to go” was said in his own natural but silent voice. The TV was on, and his eyeballs were aimed at it, but he was not paying any attention to it.

3. Christine was looking down at her pinky toe and innerly saying, “My pinky toe is ugly.” This was said in her normal voice with a mildly discouraged tone and inflection.

4. Daphne was talking on the phone to a United Blood Services representative, who was telling her she would get two free tickets to the Fabulous 4 concert if she donated blood. At the moment, Daphne was innerly saying “That is so awesome!” in her own voice with an excited tone that conveyed the excitement she felt about taking her daughter to the concert.

5. Ellen was watching the TV show Cops. The cops had wrestled a guy to the ground and the sirens were continuously going off. At the moment of the beep Ellen was hearing the profoundly annoying/unpleasant sirens and innerly yelling, “Turn those sirens OFF!!” yelled in her own voice with an extremely annoyed/frustrated tone. Ellen was simultaneously paying attention to the TV show, especially the blue and red flashes at the left.

6. Fayth was in the bathroom straightening her hair. At the moment, she was innerly saying to herself, “This year can still be better.” She innerly said this in her own voice as if she were giving herself a pep-talk with emphasis on the word can. She was also attending to what she was doing.

By synthesizing insights gleaned from such records, Hurlburt and his collaborators have just published one of the most comprehensive and fascinating studies about the characteristics of inner speech. To start, the psychologists emphasize that although inner speaking is ubiquitous, its frequency varies dramatically from one person to the next. One woman, for example, was speaking inwardly at the time of 17 out of 18 beeps. In contrast, other people were never talking to themselves silently at the time of the beep; rather, they were experiencing another mental phenomenon, perhaps absorbed in a flashback, inundated with a wave of emotion or spatially rotating an object in their mind's eye. On average, volunteers spoke silently in 22 to 25 percent of recorded mental moments, which corroborates earlier research suggesting inner speech occupies one quarter of conscious experience.

Some people reported feeling that inner speaking originated in their torso; others said it took place in the head; still others did not associate it with any body part. Sometimes people talked to themselves in a single voice; other times in chorus. Now and then individuals adopted the voices of their friends when rehearsing dialogue—an almost exact replica of the other person's voice in some cases, a less realistic imitation in others.

Inner speech is remarkably similar to spoken dialogue in many ways and, at the same time, clearly has some very unique features. People might omit a word or two from a silent thought, for instance, without breaking the cadence of the sentence: "I want to take ____ out for a walk this afternoon," where the blank space is understood to be "the dog," even though that phrase is not actually verbalized in one's mind. Our minds can also say Yes! at the same time our lips speak No; we might think chicken and choose fish. In everyday life, such contradictions often go unnoticed; they only became apparent to volunteers in studies because the beepers forced them to pay attention. The often speedy and sometimes fragmentary nature of inner speech may explain the mismatch. Perhaps we explore simple decisions or possible verbal responses almost simultaneously, so it may seem our audible speech or actions oppose our minds when in fact we just didn't catch everything we were thinking.

Indeed, some evidence suggests that when talking to ourselves in our heads, we can articulate and comprehend far more sentences and ideas than we could by speaking aloud for the same amount of time. Woolf relished the mind's ability to dilate a given moment in time. In her novels, she sometimes spends several pages examining a few minutes or even seconds from several characters' perspectives, transcribing many more silently spoken sentences onto the page than could ever have escaped their mouths in those brief timespans. Her characters spend much more time conversing with themselves than with anyone else. Even if that is not true for everyone outside her novels, it is difficult to exaggerate the importance of inner speech. Yes, many silent thoughts are—like some of Hurlburt's six examples—seemingly mundane or trivial. But what Woolf recognized, and what some psychologists have also argued, is that we depend on the totality of our inner chatter, even the more banal bits, to construct something incredibly fundamental: our sense of self.

What we call the self is a story that we continuously write and rewrite in our minds—a narrative that appears to rely, at least in part, on verbal thought specifically. Merely reacting to the world around oneself by talking to oneself about it may be essential to maintaining a cohesive identity that persists through the past, present and future. In 1972, a stroke robbed clinical psychologist Claude Moss of both audible and inner speech. "In other words," he wrote, "I did not have the ability to think about the future—to worry, to anticipate or perceive it—at least not with words. Thus for the first four or five weeks after hospitalization I simply existed.” Similarly, Helen Keller has written that, before she could think in language, “I did not know that I am. I lived in a world that was a no-world. I cannot hope to describe adequately that unconscious, yet conscious time of nothingness." Descartes would nod in agreement. Unless we talk to ourselves, we are not ourselves.

Related Reading:

A Contemplation of Chattering Minds

Mrs. Dalloway in New York City: Documenting How People Talk to Themselves in Their Heads

Speak for Yourself (feature article in upcoming issue of Scientific American MIND)