The silent inner world of anendophasia

As you go about your day, do you often hear an inner voice in your mind? Mine is forever saying things like, 'you really don't need that chocolate' or 'you can't forget to pack the kids' PE kit.'

'Inner speech', 'verbal thoughts', or an 'inner voice' — whatever name you prefer, this phenomenon has been widely considered a universal aspect of the human experience. However, recent research has challenged this idea. Now, a new paper in Psychological Science proposes a name for an absence of inner speech — 'anendophasia' — and finds that it affects people's performance on certain cognitive tasks.

Johanne S. K. Nedergaard at Aarhus University, Denmark, and Gary Lupyan at the University of Wisconsin-Madison recruited participants who, as part of other research, had already completed an assessment of their internal representations. A portion of this assessment focused on the inner voice, and asked about levels of agreement with statements such as 'I think about problems in my mind in the form of a conversation with myself.' For their new research, Nedergaard and Lupyan studied 46 people who'd received the lowest scores for this, and who had a near-absent an inner voice, and 47 people who fell at the other end of the spectrum, reporting near-constant inner speech.

In the first of four tasks, these participants were repeatedly shown pictures of pairs of objects and asked whether the names of those objects rhymed. While the two groups took about the same length of time to reach a decision, the results showed that those with a near-absent inner voice got poorer scores. In the second task, the participants were briefly shown sets of five words and then asked to reproduce them. Again, overall, this group didn't do as well.

However, for both of these experiments, the researchers also asked the participants whether they had said the task words out loud. A similar proportion of both groups said that they had, and when only the scores of these participants were compared, the group with a near-absent inner voice had performed just as well as the other group. This suggests that when they spoke the words out loud, this compensated for their lack of inner speech. Overall, the findings also suggest that participants without anendophasia used verbalisation strategies internally, the researchers write.

A third task explored the participants' ability to switch quickly from one task to another — in this case, from adding numbers to subtracting them. Earlier studies have suggested that inner speech may help us to make this type of shift. However, Nedergaard and Lupyan found no differences in the performance of the two groups.

Finally, the researchers looked for any differences in 'category effects' for visual discrimination. Most of us are quicker to distinguish between two images that belong to different categories — for example, a silhouette of a cat and a silhouette of a dog — than between two images that belong to the same category — such as two cats — even if the degree of visual difference between the objects in each pair is the same. There is evidence from research into colour perception, for instance, that language supports the formation and separation of different concepts. However, when the researchers tested their participants with dog-cat and cat-cat silhouettes, there were no differences between the two groups.

Overall, this work reveals some differences — and some similarities — in how people with a near-absent versus a near-constant inner voice perform at these everyday-type tasks.

It also adds to a growing understanding that there can be quite stark differences in the human mental experience. With visual imagery, for example, it's now well-established that while some people experience plenty, others report little, or even none. A lack of visual imagery is known as 'aphantasia'. The researchers write that the coining of this term back in 2010 helped coordinate research into this phenomenon (for example, a new study suggests that it's associated with poorer recollection of personal experiences), and also the development of an online community (r/aphantasia). They hope the same might now happen for anendophasia.

For now, though, this new work shows that there are real, behavioural consequences of experiencing less inner speech — though, as the researchers write, "that these differences may often be masked because people with anendophasia use alternative strategies."  

Read the paper in full:

Nedergaard, J. S. K., & Lupyan, G. (2024). Not Everybody Has an Inner Voice: Behavioral Consequences of Anendophasia. Psychological Science, 0(0). https://doi.org/10.1177/09567976241243004