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How exactly do children acquire language? And do they do so in the same way worldwide? Aoju Chen, professor of English linguistics: language development, conducts research into language acquisition worldwide. "By comparing children worldwide, we learn more about the characteristics that are universal and those that are more influenced by culture and the specific language."

How does global engagement take shape in your field?

"Global engagement in language development research takes shape in several key ways and has important added value. First, researchers take a cross-linguistic approach, comparing how children learn different languages to find both universal patterns and language-specific differences. This allows hypotheses to be tested more rigorously for their generalizability, either to children acquiring any language or to those learning a specific language. 

For example, many studies conducted in WEIRD (Western, Educated, Industrialized, Rich, and Democratic) populations (mostly with Englishspeaking children) have found that nouns—words for objects like “dog” or “ball”—are learned earlier and more easily than verbs (like “run” or “eat”). This led to the widespread assumption that children universally show a noun advantage in early language development. However, when researchers began studying non-WEIRD languages, like Korean and Mandarin Chinese, they found that this pattern was not universal. Children learning these languages show a verb advantage and tend to learn verbs earlier than English-speaking children. This demonstrates that how children learn words is shaped by the structure of their language, not just by universal cognitive processes. The initial over-reliance on WEIRD samples led to misleading conclusions about early word learning."

Collaboration through sharing data

"Another way of global engagement in language development research is large-scale collaboration. Teams from different countries work together and share data through resources like CHILDES or Wordbank. A great example of a recent large-scale collaboration is the ManyBabies initiative, where researchers worldwide pool data and resources to study language development in infants. One of the ManyBabies projects, for example, examined whether infants across different languages prefer infant-directed speech, helping us understand if this preference is universal.

International conferences also play a crucial role in fostering global engagement in infant and child language development research. In 2024, the 16th Congress of the International Association for the Study of Child Language and the 24th International Congress of Infant Studies took place. These conferences recur every three and four years, respectively. They are indispensable in bringing together students, scholars, and professionals from different countries and linguistic backgrounds to share findings, debate theories, and build collaborations."

What is your research about?

"My own area of language development research focuses on how children learn the prosodic system of their native language. Prosody refers to variation in pitch, duration, and intensity in speech. It plays a crucial role in the structure of speech, grouping words into meaningful units within speech streams, much like punctuation marks in written language. Prosody is also vital for communication. It carries many functions, such as highlighting new information in a sentence, distinguishing questions from statements (e.g., ‘Coffee?’ vs. ‘Coffee.’), and conveying emotion (e.g., happy vs. sad). The exact way prosody is used to structure speech and convey meaning varies from language to language. My team and I have been studying how children learn the prosodic system of their native language. We study the factors that can influence the rate and route of learning, as well as the mechanisms that drive developmental changes. In my research, it is necessary to study children acquiring different languages.

For example, in my completed VIDI project on how children learn to use prosody to demarcate new information in communication, also known as ‘focus’, my team studied children aged 4 to 11 years learning Korean, Swedish, Mandarin Chinese, and Dutch, in collaboration with international partners. One of the hypotheses was that higher transparency of the form-meaning mapping between prosody and focus would lead to a faster rate of learning. We tested it by comparing children’s use of prosody in Stockholm Swedish, Seoul Korean and Dutch, relative to adults, because these languages differ in the transparency of the prosody focus mapping. This mapping is most transparent in Stockholm Swedish, followed by Seoul Korean, and least transparent in Dutch. We found that Swedish-learning children become adult-like in their use of prosody to mark focus at the age of four or five years, Dutch-learning children at the age of ten of eleven, and Seoul Korean-learning at the age of four or five in some aspects, but at the age of ten or eleven in other aspects. These findings thus support our hypothesis on the effect of transparency of form-meaning mapping in the acquisition of prosodic focus marking.

In my ongoing VICI project on early prosodic development, my team, together with our national and international collaborators in Indonesia, Sweden, and Germany, has been investigating how innate and learned mechanisms drive the rapid development of prosody before birth and during the first three years of life. One of our hypotheses on innate mechanisms is that infants initially rely on the so-called Effort Code in their use of pitch to interact with caregivers (a focus in the PhD project of Elanie van Niekerk). The Effort Code describes the physiological connection between greater articulatory effort and a larger pitch range, i.e. the difference between the highest and lowest pitch in speech. It predicts that a larger pitch range signals a more engaged speaker and a more emphatic message.

Suppose the Effort Code indeed drives early prosodic development. In that case, we expect to see infants across different languages initially using a large pitch range in vocalisations produced when interacting with a new toy compared to vocalisations produced when interacting with a familiar toy. To test this, we studied Dutch- and Indonesian-learning infants aged three to seven months. We chose these two languages because Dutch speakers use a larger pitch range to mark new information, whereas Jakarta Indonesian speakers do not rely on pitch variation for this purpose. We expect that at three months, infants in both language groups will use a larger pitch range in their vocalisations when playing with a new toy than when playing with a familiar toy. However, as they develop, we predict that Dutch-learning infants will reinforce this pattern, while Indonesian-learning infants will reduce their use of pitch variation for this function. We recently completed data collection in both Indonesia and the Netherlands, and we are excited to begin analysing the data."

What advice would you give to colleagues who are interested in getting involved in global/international collaborations?

"A strong partnership forms when researchers share common goals while bringing complementary expertise to the table. If you find collaborators who are truly invested in the same big questions, the rest of the process becomes much easier.

International projects are exciting, but they’re also logistically complex. You’ll likely deal with funding differences, variations in research infrastructure, and even different ways of working. Instead of seeing these challenges as obstacles, it helps to approach them as part of the process. If you decide to join an international initiative, be prepared to stay committed, even when things get complicated.

If you’re starting an international collaboration, be upfront and transparent and make sure that everyone involved understands what you’re hoping to achieve, what their role is, what they will gain from the collaboration, how decisions will be made, and how their input will be valued. During the collaboration, it is important to create an environment where people feel comfortable raising concerns and providing feedback, and have a say in the parts of the project that affect them most. And no matter how busy things get, taking the time to acknowledge milestones, even in small ways, can help keep everyone motivated and connected."

What do you see as the value of global engagement more generally within child- and youth studies?

"Children grow up in vastly different cultural, social, and economic contexts, which shape their development in unique ways. Global engagement enables researchers to examine how childhood and youth experiences vary across societies, leading to more accurate and globally relevant theories of child development.

Moreover, many of the most pressing issues in child and youth studies, such as mental health, access to education, poverty, migration, and digital exposure, are global. Language skills are deeply intertwined with these challenges, influencing learning opportunities, social integration, and overall well-being.

Effectively addressing these issues requires cross-border collaboration, where researchers share data, compare interventions, and develop solutions that can be adapted to different cultural and linguistic contexts. By working together globally, we can build a more inclusive and comprehensive understanding of child and youth development, ensuring that research findings benefit children and young people worldwide."