Solo adults: How varying languages influence the way we speak to babies

Research has confirmed that adults modify their speech when talking to infants, a phenomenon known as infant-directed speech (IDS). This specialized communication style, which differs from typical adult conversations, involves changes in pitch, vocabulary, and sometimes exaggerated vowel sounds. A particularly debated aspect of IDS is vowel hyperarticulation—where vowels are pronounced more clearly—aimed at aiding infants' language learning.

A recent comprehensive meta-analysis conducted by scientists from the International Research Center for Neurointelligence (WPI-IRCN) at The University of Tokyo, along with colleagues from the University of Amsterdam, PSL University, and Aarhus University, examined existing studies on vowel hyperarticulation in IDS across multiple languages and research methods. Their findings, published in the journal Psychological Bulletin on June 2, 2025, reveal that mothers in at least 10 languages tend to exaggerate vowels when speaking to babies.

Earlier studies suggested that vowels such as "a," "i," and "u" are often hyperarticulated to make speech clearer for infants, facilitating word recognition and learning. However, newer research showed inconsistent evidence, with some studies indicating that such exaggeration may be a by-product of positive emotions like smiling.

"We conducted this meta-analysis to understand whether vowel hyperarticulation is a genuine feature of speech directed at infants and to identify the factors influencing it," explained researcher Irena Lovčević. The analysis encompassed 20 studies using similar methodologies and 35 with varied approaches, combining their results for stronger statistical validation.

The results confirmed that vowel exaggeration occurs in at least 10 languages, but the researchers emphasized the importance of standardized methodologies, as variations in measurement scales and research designs can influence findings. They also highlighted that smaller sample sizes and underrepresentation of certain languages limit the ability to make broad generalizations.

Moving forward, the team aims to explore other aspects of infant language development, focusing on environmental factors such as speech exposure and caregiver-baby vocal interactions. Understanding these elements could provide insights into how babies learn to speak effortlessly.

This research underscores the significance of speech modifications like IDS in early language acquisition and encourages more cross-linguistic and cross-cultural studies to deepen our understanding of how children acquire language around the world.