Hemodynamic Responses to Word Forms in Japanese Infant-Directed Vocabulary in 5- and 9-Month-Old Infants: Early Sensitivity to Prosodic Structure and Emergence of Prosodic Representations.

Overview

1. Information & Management Systems Engineering Nagaoka University of Technology Niigata Japan
2. RIKEN Center for Brain Science Wako Japan
3. Center for the Research and Support of Educational Practice Tokyo Gakugei University Koganei Japan
4. Department of Psychology & Neuroscience Duke University Durham North Carolina USA

Abstract

The prosodic characteristics of a native language greatly influence early language acquisition. Yet, Japanese mothers are known to use a specific prosodic structure in infant‐directed vocabulary (IDV)—specifically, three‐mora, two‐syllable words with a heavy‐light pattern—which, crucially, differs from the standard prosodic rhythm of adult vocabulary. This study used near‐infrared spectroscopy to examine hemodynamic responses to the Japanese IDV form in 5‐month‐old (n = 31) and 9‐month‐old (n = 34) Japanese infants, targeting the period before and during the emergence of this preference. The results revealed that oxygenated hemoglobin was greater for the IDV form than for the non‐IDV form in the left superior temporal gyrus (STG) for both age groups, consistent with the advantage of the IDV form observed in previous behavioral studies. Furthermore, this effect was localized to the left middle and left posterior STG in 5‐ and 9‐month‐old infants, respectively, highlighting early sensitivity to its prosodic structure followed by the emergence of phonological representation. This cortical shift, along with an observed trend toward adult‐like patterns, may suggest a broader transition from perceptually accessible IDV structures to the more diverse patterns of standard adult vocabulary. Although 5‐month‐old infants who have not yet exhibited a preference for the IDV form may not have developed specific phonological representations, their brains' ability to process its prosodic pattern could serve as a foundation for subsequent learning. These findings demonstrate that the specific structure of Japanese IDV acts as a foundational scaffold, guiding the transition from initial prosodic tuning to mature word‐level processing.

Summary: Early sensitivity to prosodic structure was observed in 5‐month‐old Japanese infants. Emerging phonological representation was observed in 9‐month‐old Japanese infants. Japanese infant‐directed vocabulary form serves as a prosodic template.

Reproduced under the paper's license (CC BY), from the paper cited above.

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Data

Datasets cited

• osf:ngcef, at OSF; found in “Data Availability Statement”

Data Availability Statement

Research data is available on the Open Science Framework (https://osf.io/ngcef/).

Reproduced under the paper's license (CC BY), from the paper cited above.

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Version 2, 28 September 2026

• Publisher: n/a → Wiley

Version 1, 27 September 2026: the first record

Recorded: type, language, journal, volume, issue, pages, dates, 6 authors, 6 keywords, 13 MeSH terms, 3 funders, 60 references.

Cite

This paper

Akimoto, Y., Takahasi, M., Yamane, N., Tsui, R. K., Hayashi, A., & Mazuka, R. (2026). Hemodynamic Responses to Word Forms in Japanese Infant-Directed Vocabulary in 5- and 9-Month-Old Infants: Early Sensitivity to Prosodic Structure and Emergence of Prosodic Representations. Developmental science, 29(4), e70214. https://doi.org/10.1111/desc.70214

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