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A simple activity familiar to young children—counting from 1 to 5—offers a new way to study inner speech, the silent use of language in the mind. Researchers at the University of Tsukuba found that children's silent counting became increasingly consistent with age. Around age 5, children were also more likely to count entirely in their minds, without speaking aloud or moving their fingers or lips.

Tsukuba, Japan—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, the researchers developed a simple mental counting task for children aged 3-6 years 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 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.

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 and new way to investigate how inner speech develops during early childhood.

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This study was supported by the Grant-in-Aid for Transformative Research Areas (23H04830 and 23H04832) from the Japan Society for the Promotion of Science and by donations received through the academic crowdfunding platform "academist" (Project No. 396).

Original Paper

Title of original paper:

The developmental origin of inner speech: Evidence from a mental counting task in 3- to 6-year-old children

Journal:

Acta Psychologica

DOI:

10.1016/j.actpsy.2026.107716

Correspondence

Researcher OTANI Kota
Institute of Health and Sport Sciences, University of Tsukuba
(Graduate School of Sociology, Ritsumeikan University; Faculty Member, Hijirigaoka Professional Training College of Child Care)

Assistant Professor KUWAMIZU Ryuta
Advanced Research Initiative for Human High Performance (ARIHHP), Institute of Health and Sport Sciences, University of Tsukuba

Professor MORIGUCHI Yusuke
Graduate School of Letters, Kyoto University

Related Link

Institute of Health and Sport Sciences
Advanced Research Initiative for Human High Performance (ARIHHP)