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Maybe it shouldn't be surprising that writers give so many superheroes, alien beings, and magical creatures the power of telepathy. Just imagine what you could learn about a person if you could hear their thoughts.

Well, actually, I've just made a bit of an assumption there: that there'd be something to hear. Because not everyone has that kind of internal monologue—or, what psychologists often refer to as inner speech. And even people who do hear their thoughts don't necessarily talk in their heads 247.

It turns out that inner speech could tell us a lot about how our brains work, how they develop, and how we speak. But… research on all this is really just getting started. Inner speech is somewhat loosely defined as when a person “speaks” meaningful thoughts without producing sound or moving any part of their body, like their tongue or their lips.

Though, in some ways, it's easier to define by what it isn't. It's different from visualizing or picturing things in your head. And it doesn't include feelings like happiness or hunger, or your awareness of sensory experiences, like noticing the glint of something shiny on the ground.

So basically, it only refers to thoughts accompanied by specific words. These words usually have the same tone, inflection, and even accent that they would if were spoken aloud—though not always, which we'll get to in a bit. Even figuring that much out about inner speech was somewhat of a challenge for psychologists, because—surprise!—it's really hard to measure people's internal experiences.

So there's been a lot of variation in research methods, and not a lot of agreement between different studies and different scientists. For example, some studies have tried to see inside people's heads by prompting them to hear specific words or phrases in their mind—like, by asking them to read something silently or determine if two words rhyme without saying them out loud. That's revealed some weird quirks about inner speech—like that, when people read, they're actually much more likely to mentally say single words that represent a passage than every word of every sentence.

But prompted inner speech and spontaneous inner speech aren't really the same. Plus, prompts can't tell us much about how frequently or why people use inner speech in their daily life. So, some researchers use questionnaires instead.

According to those, these conversations we have with ourselves are generally about... ourselves. And kind of in a bad way. Most of the time, our inner speech consists of negative things about ourselves, our negative emotions, or us trying to decide if we're good enough.

And, weirdly enough, that's all usually in full sentences. Only about one-third of people experience abbreviated inner speech, where a single word or phrase represents an entire complex thought. So… the opposite of what happens when we read.

Questionnaires have also tried to get at the question of how often people engage in inner speech, but they have a few limitations. Perhaps the most glaring is that people generally aren't great at being aware of their inner experiences, so questionnaires probably overestimate the frequency of inner speech. More recently, researchers have started using a procedure called.

Descriptive Experience Sampling, or DES instead. With DES, people carry a beeper that goes off randomly throughout the day. And when it does, they write down some notes about exactly what was going on in their head at that moment.

It's like when you're sitting across from your friend and you're like “what ya thinking about?” It's not perfect. Some researchers think that DES goes too far and underestimates inner speech, for example. But it is giving scientists a better sense of how many people “hear” their thoughts and how often.

And it's revealed that inner monologues—like most things in psychology—are on a spectrum. Very few people have no inner speech at all, and very few people engage in it one hundred percent of the time. DES studies suggest that seventy to eighty-five percent of people experience some kind of spontaneous inner speech at least occasionally.

And of those people, most of them are talking to themselves about fifteen to thirty percent of the time. It's also possible to have more than one internal experience simultaneously, so you might be visualizing something and talking to yourself about it. And inner speech varies in other ways, too.

While a lot of people talk about this in terms of internal monologues, about seventy-five percent of people report that sometimes they're having back-and-forths in their head. They usually play both parts in the conversation, though—only about twenty-five percent of people report that other people show up in their inner speech. People who have ever had an imaginary friend are more likely to use this kind of dialogic speech, even if they don't have that friend anymore.

Which is pretty cute. Others might experience something a little different but similar: what psychologists call imagined interactions. Basically, that's when you imagine all the things you should have said to that guy who stole your parking spot, or rehearse what you're going to say to your date later.

What's not clear in all of this is why people have different inner monologues or dialogues, and what those differences say about them. We don't even really know where inner speech comes from. From an evolutionary standpoint, many experts think that inner speech came about as part of the process for generating overt speech.

It may even be a side effect of sorts of spoken language that's been co-opted for other cognitive tasks. See, when you go to speak, your brain simultaneously sends signals to two different areas: one to motor parts of the brain to control the mouth and the tongue and stuff, and a copy to the sensory parts of the brain. The sensory signal allows the brain to make a prediction about what it's about to hear.

Essentially, you recite words in your head as you say them out loud. And it turns out that same kind of signal occurs during inner speech. That may be why you can quote “hear” yourself—you're literally activating the hearing part of your brain.

And some psychologists think this means the underlying purpose of internal speech is to catch errors when you talk. If the internal prediction matches what you say, your brain knows it can filter your words out of what it's hearing and focus on the rest of the sounds coming in. If they don't match—like if you stumble over a word—your brain lets you know that you made a mistake so that you can stop and correct yourself.

But it doesn't seem like this error correction is absolutely essential for speech, because the two can be separated from one another. There are cases of people with brain damage who lose their inner speech but not the ability to talk, and vice versa. Still, inner speech could have helped people communicate better, which could explain why it evolved.

This is just the prevailing hypothesis, though, and it's possible it's wrong. Also, it's likely that even if inner speech started this way, the brain has repurposed it for other uses. Those other uses might explain why it differs between people.

Some psychologists think our everyday inner speech reflects conversations that we had out loud as kids—especially moments when our caregivers talked us through solving a problem or calmed us down. The idea is that these teaching moments get internalized as we grow up, and then we essentially replay them in our heads later—which would explain why inner speech often resembles a conversation. And, this could explain why, content-wise, it's often about self-regulation—things like problem-solving, planning things out, time management, and motivation.

Those are all things someone would help talk their young child through. Plus, the same brain areas are activated during internal dialogic speech and when a person is thinking about someone else's experience and perspective. That would make sense if the voice in your head is basically your brain recycling someone else's words.

So, if this theory is correct, inner speech might be different between people simply because their upbringings and social interactions were different. We still don't know how or if those differences matter, mind you. But there are some big clues that inner speech plays an important role in cognition—so, all those brain processes involved in thinking.

For instance, scientists have used a test called a dual-task paradigm to see how inner speech affects problem solving. Basically, they ask the person to solve a problem while doing something else. And if that second task is physical—like, tapping their foot—they generally have no problem with it.

But if it's verbal—like, remembering a list of words—then they perform worse. Researchers think that's because those words disrupt their inner speech, making it so they can't really talk themselves through the problem. Inner speech may also be an important tool for memory, and more specifically, working memory.

That's the memory where you store the information you want to access really quickly. One of the components in working memory is the ability to repeat information to yourself until you no longer need it—and for that, you need inner speech. In fact, people who do more self-managing inner speech—so, things like talking themselves through solving a problem—do seem to do better on some cognitive tasks.

So differences in how people talk to themselves might underlie differences in how well they perform different kinds of thinking. Inner speech may also play a part in mental health conditions. Research has connected it to depression and anxiety, for example.

People who have more depressive tendencies tend to experience more depressive self-talk. And we know that people who are more anxious tend to engage in more self-critical inner speech. It's not clear if these negative forms of inner speech exacerbate or even cause those conditions, or if the conditions lead to higher amounts of negative inner speech.

Though, studies have found that if you ask people to think verbally about hypothetical situations—even positive ones—their mood is lower than if you ask them to picture the hypothetical situations instead. And that does support the idea that the speech part of inner speech might make people less happy… for some reason. Other research has tied inner speech to symptoms common in psychotic disorders.

For example, people with schizophrenia often report hearing voices of people speaking to them or telling them what to do. One theory is that those “voices” are actually inner speech. Remember that prediction signal I mentioned earlier?

Well, some experts think that if something in that neural circuit is off, then the brain's usual way of identifying self-made sounds and thoughts could be off, too. So basically, that person's brain might not be so great at separating sounds they generate from ones they hear. And that may mean it also attributes inner speech to someone else.

Because of these potentially important roles in cognition and mental health, psychologists are eager to gain a better understanding of what inner speech is and why it happens. And figuring all that out could tell us a lot about, well, a lot—from how our brains develop and work to what's actually happening in a variety of mental disorders. But as of right now, we just don't know that much about this thing most of us do every day.

There are a lot of big questions currently unanswered, like where inner speech comes from, why it differs between people, and what those differences mean. Like, can you change your inner monologue? Can you train yourself to think in conversations, or to hear other voices or your own more often?

We don't even know if you should want to make those changes—if there are the benefits or downsides of different kinds of inner speech. And it's probably going to be a while before we have any clear answers, because our methods for studying it just aren't great, and there's a lot of debate over basic questions, like how many people even do it in the first place. In the meantime, though, you can still talk about it amongst yourself.

Thanks to Eric for asking us about this topic, and to all our other patrons who support us on Patreon. We love hearing what you want to learn about! If you're one of our awesome patrons, be sure to hit up that QQ inbox from time to time, or jump onto the Discord to nerd out about sciencey things with other patrons and some of our staff.

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