計画班A01の大谷康太さん、計画班A03の森口佑介さんらの研究グループによる論文が、国際学術誌「Acta Psychologica」に掲載されました。大谷さんは元A03班の大学院生であり、現在は桑水隆多さんが参画するA01班の研究員として研究を進めています。

　本研究では、3～6歳の幼児を対象に、「1から5まで頭の中で数える」というシンプルな課題を用いて、外から直接観察することが難しい「内言（inner speech）」の発達を検討しました。その結果、年齢とともに頭の中で数える時間が安定し、5歳頃から声や指に頼らず、頭の中だけで数えられるようになることが示されました。

内言は、私たちが声に出すことなく頭の中で用いている言葉であり、思考や注意、自己制御などに関わると考えられています。本研究は、「数を数える」という身近な行動を利用することで、幼い子どもが言葉で報告することの難しい内言の発達を捉えられる可能性を示すものです。

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Paper Information

Authors: Kota Otani, Ryoichi Watanabe, Ryuta Kuwamizu, Nozomi Yamamoto, Yusuke Moriguchi

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

Journal: Acta Psychologica, Volume 270, 107716 (2026)

DOI: https://doi.org/10.1016/j.actpsy.2026.107716

Abstract

  Inner speech is a pivotal cognitive tool, yet its developmental timeline remains controversial due to methodological limitations of existing tasks. Specifically, complex memory demands often mask early competence, and self-report measures rely on introspective skills that young children lack. To address these issues, we introduced a novel “Mental Counting Task,” a simple paradigm feasible even for preschoolers, to objectively map the early developmental trajectory of inner speech. Participants, children aged 3 to 6 (N = 58) and adults (N = 25), performed five trials of serial number chanting (1 to 5) in both Overt (chanting aloud) and Inner (chanting silently) Speech conditions at a consistent speed, alongside a self-report inner speech scale. We focused on the stability of counting speed by analyzing the Relative Standard Deviation (RSD), a coefficient of variation that normalizes variability, to evaluate temporal stability across these trials. Results showed that RSD was significantly higher in the Inner Speech condition across all ages, reflecting inherent instability due to the lack of sensory feedback. Notably, RSD in children significantly decreased with age, capturing the gradual stabilization process of inner speech. In contrast, self-report scores showed no correlation with counting performance, underscoring the immature metacognition of preschoolers. Additionally, task completion data indicated that stable inner speech becomes robust around 5 years of age, earlier than previously assumed. These findings demonstrate that RSD in this paradigm serves as a sensitive marker for the maturation of inner speech, providing a new solution for elucidating its developmental origins.

プレスリリース

筑波大学

「1から5まで数えることで、幼児の『頭の中の言葉』が測れる」