The vast majority of people have an ongoing conversation with themselves, an inner voice, that plays an important role in their daily lives. But between 5% and 10% of the population do not have the same experience of an inner voice, and they find it more difficult to perform certain verbal memory tasks, new research shows.

Previously, it was commonly assumed that having an inner voice had to be a human universal. But in recent years, researchers have become aware that not all people share this experience.

According to postdoc and linguist Johanne Nedergård from the University of Copenhagen, people describe the condition of living without an inner voice as time-consuming and difficult because they must spend time and effort translating their thoughts into words:

"Some say that they think in pictures and then translate the pictures into words when they need to say something. Others describe their brain as a well-functioning computer that just does not process thoughts verbally, and that the connection to loudspeaker and microphone is different from other people's. And those who say that there is something verbal going on inside their heads will typically describe it as words without sound."

Harder to remember words and rhymes

Johanne Nedergård and her colleague Gary Lupyan from the University of Wisconsin-Madison are the first researchers in the world to investigate whether the lack of an inner voice, or anendophasia as they have coined the condition, has any consequences for how these people solve problems, for example how they perform verbal memory tasks.

People who reported that they either experienced a high degree of inner voice or very little inner voice in everyday life were subjected to one experiment that aimed to determine whether there was a difference in their ability to remember language input and one about their ability to find rhyme words. The first experiment involved the participants remembering words in order—words that were similar, either phonetically or in spelling, e.g., "bought," "caught," "taut" and "wart."

"It is a task that will be difficult for everyone, but our hypothesis was that it might be even more difficult if you did not have an inner voice because you have to repeat the words to yourself inside your head in order to remember them," Johanne Nedergård explains.

"And this hypothesis turned out to be true: The participants without an inner voice were significantly worse at remembering the words.

"The same applied to an assignment in which the participants had to determine whether a pair of pictures contained words that rhyme, e.g., pictures of a sock and a clock. Here, too, it is crucial to be able to repeat the words in order to compare their sounds and thus determine whether they rhyme."

In two other experiments, in which Johanne Nedergård and Gary Lupyan tested the role of the inner voice in switching quickly between different tasks and distinguishing between figures that are very similar, they did not find any differences between the two groups. Despite the fact that previous studies indicate that language and the inner voice play a role in these types of experiments.

"Maybe people who don't have an inner voice have just learned to use other strategies. For example, some said that they tapped with their index finger when performing one type of task and with their middle finger when it was another type of task," Johanne Nedergård says.

The results of the two researchers' study have just been published in the article "Not everybody has an inner voice: Behavioural consequences of anendophasia" in the journal Psychological Science.

Does it make a difference?

According to Johanne Nedergård, the differences in verbal memory that they have identified in their experiments will not be noticed in ordinary everyday conversations. And the question is, does not having an inner voice hold any practical or behavioral significance?

"The short answer is that we just don't know because we have only just begun to study it. But there is one field where we suspect that having an inner voice plays a role, and that is therapy; in the widely used cognitive behavioral therapy, for example, you need to identify and change adverse thought patterns, and having an inner voice may be very important in such a process.

"However, it is still uncertain whether differences in the experience of an inner voice are related to how people respond to different types of therapy," says Johanne Nedergård, who would like to continue her research to find out whether other language areas are affected if you do not have an inner voice.

"The experiments in which we found differences between the groups were about sound and being able to hear the words for themselves. I would like to study whether it is because they just do not experience the sound aspect of language, or whether they do not think at all in a linguistic format like most other people," she concludes.

More information: Johanne S. K. Nedergaard et al, Not Everybody Has an Inner Voice: Behavioral Consequences of Anendophasia, Psychological Science (2024). DOI: 10.1177/09567976241243004