Counting to 5 reveals how children's 'inner speech' develops
· Medical Xpressedited by Sadie Harley, reviewed by Robert Egan
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Even when we are not speaking aloud, we often talk to ourselves in our heads, using language to guide our thoughts and actions. This is known as "inner speech" and is involved in cognitive functions such as attention and self-control. However, studying how inner speech develops is challenging, particularly in young children, who may not yet be able to clearly describe what is happening in their minds.
To address this challenge, researchers at the University of Tsukuba developed a simple mental counting task for children ages 3–6 and adults. Participants counted from 1 to 5 five times aloud and five times silently, attempting to maintain the same pace across trials. The researchers measured the variability in counting time across repetitions and compared this variability between aloud and silent counting. Participants were also asked whether people could use words in their heads without speaking aloud.
The study is published in the journal Acta Psychologica.
Silent counting steadies with age
The results showed that silent counting became more consistent with age: Older children showed less variation in the time required to count from 1 to 5 across repeated trials. Counting aloud did not show the same age-related pattern, suggesting that the developmental change was not simply attributable to improvements in counting ability.
The researchers also examined whether children could count entirely in their minds, without speaking aloud or moving their fingers or lips. Children who were able to do so were older than those who were not. Together, these findings suggest that the ability to count entirely in the mind becomes increasingly stable during early childhood, with around age 5 emerging as an important developmental point.
Using inner speech before recognizing it
Adults were also much more likely than children to understand that people can use words in their heads. Among the children, however, this explicit understanding was not related to performance on the mental counting task. This finding suggests that children may be able to use language internally before they can explicitly recognize or describe this ability.
The findings demonstrate that a simple counting task can capture developmental changes in inner speech without specialized equipment or complex procedures. This approach therefore provides a simple, new way to investigate how inner speech develops during early childhood.
More information
Kota Otani et al, The developmental origin of inner speech: Evidence from a mental counting task in 3- to 6-year-old children, Acta Psychologica (2026). DOI: 10.1016/j.actpsy.2026.107716
Clinical categories
PediatricsChildren's healthPsychology & Mental healthPsychiatry Provided by University of Tsukuba Who's behind this story?
Sadie Harley
BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries. Full profile →
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