Do you ever hear a voice in your mind? Maybe it’s reminding you to pick up groceries on your way home, or berating you for forgetting your friend’s birthday, or rehearsing a conversation you’re about to have with your boss.
Most of us experience an inner voice at some point. We might call it an internal monologue, thinking in words or talking in our head; psychologists call it ‘inner speech’. But there’s growing evidence that some people have no inner voice at all.
“I have no speech or words in my mind whatsoever. It’s always been that way for me,” says Jesse Koski, a 34-year-old who lives in Finland. “I’d always assumed that other people’s minds worked in the same way as mine.”
Psychologists recently coined a term for this phenomenon – ‘anendophasia’ – and now they’re trying to understand how common it is and how it affects those who experience it.
In the process, they’re revealing new insights into our minds’ innermost workings.
The voice within
If you’ve ever had thoughts that feel like language or words, that’s inner speech. It might feel like hearing a voice, or more like internal speaking.
It might be in your own voice or someone else’s; a solitary voice or multiple; a monologue or conversation; a full sentence (“I must remember to thank my aunt for my socks”) or a condensed phrase (“aunt socks”).
Inner speech helps us in all kinds of situations, from making decisions and solving problems to planning tasks and managing impulses. We might use it to run through past or future conversations, or to daydream and fantasise.
It can be a form of self-praise or self-criticism, and it plays an important role in working memory – the ‘mental notepad’ that we use when remembering a shopping list, say, or route directions.
The scientific study of inner speech goes back as far as the late 19th century, but research into those lacking inner speech is a relatively new area.
“People tend to assume that inner speech is universal,” says Dr Johanne Nedergaard at the University of Copenhagen, in Denmark. “But we’re becoming more aware of just how different our inner experiences can be.”
In 2023, Nedergaard showed that inner speech improves performance on tasks that are physically demanding or boring, suggesting that we use it to keep ourselves focused and motivated.
“But there were always participants in our studies who said they had no experience of inner speech,” she says.
Nedergaard and her colleague Prof Gary Lupyan at the University of Wisconsin-Madison, in the US, decided to explore the potential effects of lacking inner speech, recruiting people who scored low on a questionnaire with statements such as “I think about problems in my mind in the form of a conversation with myself.”
In their study, published in 2024, the participants were set a series of cognitive tasks and compared to people who reported high levels of inner speech.
In one task, participants were shown pairs of images (for example, a sock and a clock, or a moon and a snail) and asked whether the names of the objects rhymed.
Those with signs of anendophasia were slower and less accurate at judging rhymes, likely because they weren’t as able to mentally compare word sounds.
In another task, participants were tested on their working memory by recalling sequences of five words they’d just seen.
Those with less inner speech tended to remember fewer words correctly, perhaps due to being unable to repeat the words inside their head.
“These findings suggest that lacking inner speech has real, behavioural consequences,” says Nedergaard.
“Interestingly, when participants with less inner speech said the words out loud, their performance in the tasks matched the other group.
"So externalising thoughts – either by talking aloud or writing things down – is likely to be one coping strategy that people use in their daily lives.”
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Thought bubbles
It was a lightbulb moment for Koski when he discovered via an online video that other people have an inner voice. “When I used to watch movies that voiced a character’s inner monologue, I just thought they were doing it for effect,” he says.
“I didn’t realise people actually experienced that. My mind was blown.”
He says that his lack of inner speech doesn’t mean a lack of thoughts; it’s just that his thoughts don’t involve language.
“If you think of the mind as an ocean,” he says, “then each of my thoughts feels like a bubble rising into my consciousness. Inside the bubble is a combination of concepts, images and feelings, but no words or speech.”
Whereas someone with inner speech might think “Where did I put my keys?”, Koski says that his thought bubble might contain the concept of something missing, an image of his home with all the places the keys could be, and a feeling of dread.
He also experiences his thoughts as shimmering with colour, depending on the emotion. Surprise is pale yellow; anxiety is dark blue or purple; dread is a translucent black.
As well as speech, Koski is unable to hear music in his mind. “I recognise songs when I hear them,” he says, “but I can’t mentally play them back to myself.”
And consistent with Nedergaard’s findings on working memory, he says that he finds it difficult to remember verbal information. “I struggle with instructions. By the time I’ve been given the third step, I’ve already forgotten the second one.”
Talking to ourselves
The leading theory for inner speech traces its roots back to childhood. At an early age, children learn that language is useful for regulating and influencing behaviour.
They might receive encouragements, commands and warnings from their parents, for instance, or use their newfound speech to demand food or refuse to go to bed.
Soon, they realise that they can use language to guide their own behaviour and thinking, too. At first, this self-talk is audible – perhaps the child mutters to themself as they play – but eventually it becomes internalised, and inner speech emerges.
The fact that inner speech is so private and subjective makes it notoriously difficult to study.
Researchers often ask people to describe their experiences using questionnaires and other self-reporting techniques. But while these can provide helpful insights, their accuracy relies on people’s ability to reflect on their inner lives.
“We’re actually pretty bad at doing this,” says Prof Charles Fernyhough, director of the Centre for Research into Inner Experience at Durham University.
“People tend to answer questions based on what kind of mind they think they have or would like to have, rather than the mind they actually have.”
Another way of probing inner speech is to scan someone’s brain while they’re talking in their head.
Studies of this kind have revealed two key regions of brain activity, says Fernyhough: Broca’s area (in the left frontal lobe) and Wernicke’s area (just behind, in the left temporal lobe).
These regions also light up when we’re having conversations out loud – they’re important for speech production and speech comprehension, respectively. “When we’re using inner speech, we’re both the speaker and the listener,” he says.
The inner speech produced on demand in the lab might create quite different brain patterns compared to our more spontaneous, everyday self-talk, however.
“To learn more about the brain processes involved in inner speech, we need better methods for studying it in the wild,” says Fernyhough.
So why do some people experience less (or more) inner speech than others? “It’s an open question,” he says.
“Lots of factors could be playing a role, including differences in our brain development, brain structure, genetics and childhood social experiences.”
Silent movies
There are no words in Koski’s mind, but there are plenty of images. “Reading a book can feel like playing a movie in my head,” he says.
“If there’s a description of a character or a scene, my mind fills in all the blanks, so I get really clear visuals, and I can zoom in on whatever details I want.”
But these vivid visuals might be unusual for those without inner speech.
A 2021 study at the University of Auckland, in New Zealand, found that those who experience less ‘auditory imagery’ (which includes imagined music and other sounds, as well as speech) are also more likely to experience less visual imagery, too.
The inability to mentally visualise images, such as a favourite view or the face of a loved one, was termed ‘aphantasia’ in 2015, and there is now a thriving Reddit community (r/Aphantasia) with over 70,000 people discussing their ability (or inability) to imagine not only images but also sounds, smells, touches and tastes.
By coining the term ‘anendophasia’ – from the Greek an (lack), endo (inner) and phasia (speech) – Nedergaard and Lupyan hope to create a similar keyword that will help to catalyse research into those lacking inner speech.
It could also lead to the formation of online communities, as with aphantasia. “It’s important for people to have ways to share their experiences,” says Koski.
There is some scepticism in the psychology community about the new term, however. “It risks suggesting that this is a condition that needs to be treated,” says Fernyhough.
“I would prefer us to be emphasising that there’s huge variation in inner speech, rather than focusing on a particular group of people. It’s also unclear how many participants in this study use no inner speech at all.”
Nedergaard believes that the benefits of the term outweigh any risks. “It’s already meant a steep increase in awareness of these individual differences, both in the scientific community and the general public,” she says.
On the question of numbers, Nedergaard says that the 46 people in their ‘low inner speech’ group included both people who reported never experiencing it, and people who reported experiencing it rarely.
(There were 47 participants who reported high levels of inner speech).
Further research is needed, she says, to find out how common it is to completely lack inner speech.
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Dress rehearsal
One downside of having a speechless mind is that it can be difficult to articulate thoughts, says Koski.
“I have no way of rehearsing the words in my head, so it’s a constant process of converting my thoughts into words on the spot,” he says. “It can feel like trying to funnel an ocean through a straw.”
He compensates for this by giving himself time to gather his thoughts before speaking. “I build up what I’m trying to say and then convert it once it feels right.”
Nedergaard hopes to look at this aspect of inner speech (what she calls ‘speech planning’) in more depth. “We could carry out an experiment that involves asking people to give a presentation with very little preparation time,” she says.
“We might expect those with more inner speech to find the task easier because they’re able to use that time to prepare what to say.”
Are there any possible benefits to having less inner speech?
“You might experience less rumination, which is one of the symptoms of depression and anxiety,” says Nedergaard, who plans to investigate these potential links with mental health.
“Having lots of repetitive, negative inner speech is going to cause issues.”
On a similar theme, there’s evidence of a link between inner speech and the hallucinated voices experienced by people with conditions such as schizophrenia (see below).
One benefit for Koski is that people tell him he’s good at explaining complex ideas, which he puts down to his way of thinking.
“I love reading about new topics,” he says, “and if I learn about, say, a physics theory, it’s like all the information gets condensed into a single thought bubble, and then I can convert that back into words for others.”
Our internal experiences, it seems, are as varied and colourful as our external ones. And as researchers delve into the most mysterious aspects of our minds, they’re developing a clearer picture of the differences that make us human.
“We take so much of our inner experience for granted,” says Koski.
"It would be fascinating to have inner speech for a day, but I think it’d be a nightmare to have conversations going on in my head. I’m quite happy with how my mind works.”
Hearing voices: Inner speech and schizophrenia
People often hear their inner speech as a voice, but hearing voices can be a symptom of various mental health conditions, too – particularly schizophrenia. This has prompted researchers to look for links between them.
Growing evidence suggests that the hallucinated voices in schizophrenia occur when someone produces inner speech but doesn’t recognise it as their own – they misinterpret it as coming from someone or somewhere else.
“When you produce inner speech, an internal brain message usually gets sent to Wernicke’s area [the region of the brain that’s important for speech comprehension] telling it not to pay too much attention to what it’s about to hear, as it’s just you saying it,” says Fernyhough.
“Studies have shown that with many cases of voice-hearing, this message doesn’t get sent or is blocked, delayed or degraded in some way.”
This misinterpretation of inner speech might be more likely to happen if the voice sounds like someone else; if the person is stressed, tired or intoxicated; or if the content feels especially at odds with their sense of self (an unsettling intrusive thought, for instance).
Fernyhough is exploring how this research could lead to new treatment options for schizophrenia.
“When young people experience their first hallucinations, that’s a good time to intervene and stop things getting worse,” he says.
“Early results indicate that we can help people just by educating them about what inner speech is and where it comes from.
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