Most of us have an “inner voice,” and we tend to assume everybody does, but recent evidence suggests that people vary widely in the extent to which they experience inner speech, from an almost constant patter to a virtual absence of self-talk. “Until you start asking the right questions you don’t know there’s even variation,” says Gary Lupyan, a cognitive scientist at the University of Wisconsin–Madison. “People are really surprised because they’d assumed everyone is like them.”
A new study, from Lupyan and his colleague Johanne Nedergaard, a cognitive scientist at the University of Copenhagen, shows that not only are these differences real but they also have consequences for our cognition. Participants with weak inner voices did worse at psychological tasks that measure, say, verbal memory than did those with strong inner voices. The researchers have even proposed calling a lack of inner speech “anendophasia” and hope that naming it will help facilitate further research. The study adds to growing evidence that our inner mental worlds can be profoundly different. “It speaks to the surprising diversity of our subjective experiences,” Lupyan says.
Psychologists think we use inner speech to assist in various mental functions. “Past research suggests inner speech is key in self-regulation and executive functioning, like task-switching, memory and decision-making,” says Famira Racy, an independent scholar who co-founded the Inner Speech Research Lab at Mount Royal University in Calgary. “Some researchers have even suggested that not having an inner voice may impact these and other areas important for a sense of self, although this is not a certainty.”
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Inner speech researchers know that it varies from person to person, but studies have typically used subjective measures, like questionnaires, and it is difficult to know for sure if what people say goes on in their heads is what really happens. “It’s very difficult to reflect on one’s own inner experiences, and most people aren’t very good at it when they start out,” says Charles Fernyhough, a psychologist at Durham University in England, who was not involved in the study. Some researchers previously proposed that differences in study participants’ judgements about whether the names of different objects rhyme could serve as an objective measure of inner speech, but the new study is the first to show that lacking inner speech affects performance on some cognitive tasks.
Lupyan had previously assessed 1,037 people using a measure called the Internal Representations Questionnaire (IRQ), as part of ongoing research. For the verbal part of the IRQ participants indicate agreement with statements like: “I think about problems in my mind in the form of a conversation with myself” on a one to five scale.
For the new study, Lupyan and Nedergaard recruited 47 participants who scored the highest for having an inner voice and 46 who registered low scores—roughly in the top and bottom fifths of scores. They then gave these participants four language-related tasks they thought might be influenced by the use of inner speech. In the first, participants were briefly shown five words and asked to repeat them back. The second involved participants saying whether the names of objects in two pictures rhymed. In both experiments the group with less inner speech was less accurate in their responses. For the rhyme judgements, people with more inner speech were also faster. “This wide-ranging study really tests what inner speech gives us in terms of cognitive benefits,” Fernyhough says.
After the testing, researchers asked the participants if they had spoken aloud during these tasks. A similar proportion of both groups said they had, and when the researchers compared only those participants, the difference between the two groups disappeared, suggesting that speaking out loud compensates for lacking inner speech.
The third task tested task switching—rapidly changing from adding or subtracting, either when prompted or in alternating fashion. Previous studies have suggested that people use inner speech to direct themselves in task switching. The fourth looked for differences in participants’ ability to spot differences between two silhouettes that were from either the same or a different category (two different cats versus a dog and cat, for example), as language influences categories and labels. The groups showed no differences on these tasks. People can probably employ numerous other strategies for task switching, such as using fingers to keep track, Lupyan suggests, while inner speech may just not be helpful for visual similarity judgements.
The research may have medical implications. “Someone with more inner speech might be more reliant on language in their thinking,” Lupyan says. “So language impairment from stroke could have a more severe effect, and they may benefit from different treatments.” Understanding how inner speech develops has implications for education says Ladislas Nalborczyk, a neuroscientist at the Paris Brain Institute, who was not involved in the study. “Variations in children’s ability to represent speech sounds may impact the ability to learn the relation between sounds and writing,” he says, which in turn “may impact the way they learn to read and write, which probably has tremendous impact on their education.”
The researchers propose giving a lack of inner speech a name: “anendophasia” (from Greek: an means “lack,” endo means “inner,” and phasia means “speech”). They hope this will promote further research. noting a similar occurrence when the term “aphantasia” was coined for people who lack visual mental imagery. “It helps people find and synthesize research on a topic,” Lupyan says. “If people studying something are calling it by different names, it becomes more fragmented.” An online community also formed around aphantasia, which currently has over 60,000 members.
But there is also dissent about such an approach. “I’m not convinced coining a new term is helpful; it runs the risk of this pattern of experience being taken as a condition,” Fernyhough says. “I’d rather promote the message that diversity in inner experience should be our starting point—no two minds are the same.” Fernyhough points out that participants in the low inner speech group were just in the bottom fifth, as measured on one scale. “That’s by no means an absence of inner speech,” he says. The researchers hope to pursue this question by recruiting participants who score extremely low, to investigate whether a total absence of inner speech actually exists. “That’s definitely on the agenda,” according to Lupyan.
Inner speech also varies for a given individual. “Our inner experience can differ from moment to moment, depending on what we’re doing,” Fernyhough says. “Our work has shown that inner speech varies along a range of reliable dimensions.” This includes how much like a dialogue it is, whether it is condensed, and its emotional quality. “The interesting question for the future is whether certain kinds of inner speech can help us solve particular cognitive challenges, rather than simply how much is going on overall,” Fernyhough says.
An important avenue for future work will be obtaining more objective measures of inner speech differences, using brain imaging for instance. “You can try to decode from brain signals if a participant is hearing a voice, what kind of voice, and so on,” Nalborczyk says. “That would be the logical next step.”
For now, these differences, along with aphantasia and synesthesia (experiencing one sense as a different sense), illustrate just how different people’s inner lives can be. “It’s a huge part of the puzzle of what it means to be human,” Nalborczyk says.