Scientists discover the strange cognitive effects of living without an inner voice

Imagine going about your day without this constant inner dialogue that helps you plan, remember and self-reflect. To some, this may seem almost impossible, but new research has shown that not everyone has an inner voice. A groundbreaking study by Johanne Nedergård of the University of Copenhagen and Gary Lupyan of the University of Wisconsin-Madison examined how the absence of this inner voice, a condition they call “anendophasia,” affects various cognitive tasks.

The research was published in the journal Psychological Science.

The assumption that an inner voice is a universal human experience has influenced numerous studies of cognition and behavior. However, anecdotes and personal narratives have suggested that some people do not have an inner voice. This led Nedergård and Lupyan to investigate whether the absence of an inner voice affects cognitive tasks, particularly those involving verbal memory and language processing.

To select participants for their study, the researchers recruited people who had previously completed the Internal Representations Questionnaire (IRQ) in other, independent studies. This questionnaire measures the extent to which people experience and rely on inner speech.

They targeted participants who scored below 3.5 (putting them in the bottom 16 percent) or above 4.25 (putting them in the top 40 percent) on the verbal factor of the IRQ. A high score on the verbal factor could be achieved, for example, by agreeing with statements such as “I think about problems in my head by talking to myself.”

The final sample consisted of 93 participants, of whom 47 had high verbal scores and 46 had low verbal scores. These two groups were similar in terms of age, gender, educational level, dyslexia, and native language. The researchers designed four experiments to assess participants’ abilities on various cognitive tasks, focusing in particular on verbal memory and language processing.

The first experiment was a verbal memory task. Participants were asked to remember lists of words that were either phonetically similar (e.g., “bought,” “caught,” “tight,” and “wart”) or orthographically similar (e.g., “rough,” “cough,” “through,” “dough,” “branch”). The researchers hypothesized that inner speech helps with internal repetition and memorization of words, so people without an inner voice may have more difficulty with this task.

The second experiment was a rhyme judgment task. Participants were shown pairs of pictures and asked to judge whether the names of the objects rhymed (e.g., a sock and a watch). This task tested participants’ ability to compare phonological information without relying on inner speech.

“This is a task that will be difficult for anyone, but our hypothesis was that it might be even more difficult if you didn’t have an inner voice because you would have to repeat the words in your head to remember them,” Nedergård explained.

“And this hypothesis proved true: the participants without an inner voice were significantly worse at remembering the words. The same was true for a task in which the participants had to determine whether a pair of pictures contained words that rhymed, for example 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.”

The third experiment involved task switching, in which participants switched between different cognitive tasks, such as adding and subtracting numbers. The researchers wanted to find out whether the lack of inner speech affected participants’ ability to switch between tasks quickly and accurately. The fourth and final experiment was a visual discrimination task in which participants were asked to distinguish between very similar figures, such as different silhouettes of cats and dogs, to find out whether inner speech plays a role in visual categorization and perception.

Interestingly, the researchers found no significant differences between the two groups in the task-switching and visual discrimination experiments. This lack of differences suggests that people without an inner voice may use alternative strategies, such as physical cues, to effectively manage task switching. Furthermore, the lack of significant differences in the visual discrimination task suggests that inner speech may not be as important for visual categorization and perception as it is for verbal tasks.

“Perhaps people who do not have an inner voice have simply learned to use other strategies. For example, some said that they tapped with their index finger when performing a certain type of task and with their middle finger when performing another type of task,” Nedergård noted.

While the study highlights some cognitive differences related to the presence or absence of an inner voice, the practical implications for everyday life remain unclear. Johanne Nedergård points out that these differences may not significantly affect normal conversations, but could be relevant in certain contexts such as therapy. For example, cognitive behavioral therapy often relies on inner dialogue to identify and change negative thought patterns, suggesting that the experience of therapy may be different for people without an inner voice.

“The short answer is that we simply don’t know because we’ve only just started researching it,” said Nedergård. “But there is one area where we suspect an inner voice plays a role, and that is therapy; in widely used cognitive behavioral therapy, for example, you have to identify and change negative thought patterns, and an inner voice can be very important in such a process. However, it is still unclear whether differences in the experience of an inner voice are related to how people respond to different types of therapy.”

“The experiments where we found differences between the groups were about sound and being able to hear the words themselves. I want to investigate whether it’s because they simply don’t experience the sound aspect of language or whether, like most other people, they don’t think in a linguistic format at all.”

The researchers acknowledge several limitations of their study. One of these is the reliance on self-reported measures of inner speech, as subjective assessments can sometimes be inaccurate. In addition, the study’s sample size was relatively small, and further research with larger and more diverse populations is needed to confirm these findings.

In future research, they plan to investigate whether the lack of an inner voice also affects other areas of language. For example, it remains to be seen whether people without an inner voice think fundamentally differently and perhaps rely more on visual or abstract thought processes. The researchers also plan to investigate the possible compensatory strategies that people without an inner voice might develop to complete tasks that are normally supported by inner speech.

The study “Not everyone has an inner voice: Behavioral consequences of anendophasia” was published on May 10, 2024.