The hit animated movie “Inside Out 2” gives a voice to the emotions that race through our minds – but did you know that for some people, these little inner voices are completely silent? This astonishing phenomenon is the subject of a Danish-American study published in the journal Psychological Science.

The researchers were interested in our “internal monologue” – inner speech or verbal thoughts long believed to be inherent to the human experience. But in recent years, researchers have discovered that some people don’t hear any kind of little voice in their heads: they are said to be “anendophasic” – which literally means, a person who cannot speak internally.

Until now, this phenomenon had not been studied in depth. That’s why Johanne Nedergaard of the University of Copenhagen, Denmark, and Gary Lupyan of the University of Wisconsin-Madison in the US put a group of 46 volunteers who had a near-absent inner voice through a series of tests, and then compared their results with those of 47 people who reported near-constant inner speech.

The aim was to see if the absence of inner voice had an impact on their auditory-verbal working memory capacity. Working memory enables us to carry out complex cognitive operations such as thinking, reading, writing or counting, based on information temporarily stored in our brain. It plays a crucial role in language production and comprehension.

The authors of the study, therefore, hypothesised that the absence of an inner voice could have an impact on word memorisation. And this appears to be the case: people with an inactive inner voice performed less well on certain tasks involving their verbal memory.

“Adults who reported low levels of inner speech had lower performance on a verbal working memory task, compared with adults who reported high levels of inner speech,” the researchers wrote. In other words, the ability to mentally represent words and sounds is closely linked to the voice we hear in our heads.

Nevertheless, the experts report that some people with anendophasia seemingly compensate for this singularity by speaking the words out loud. In fact, study participants who did so were able to match the performance of those who had an inner voice.

This study is part of a growing body of scientific work suggesting that our inner worlds are far more different than we might imagine. Some people hear an inner voice, while others are seemingly unable to do so.

Whatever the case, not having an inner voice is not a pathology; it’s an individual trait like any other.