Reference: Yu, C., Suanda, S. H., & Smith, L. B. (2019). Infant sustained attention but not joint attention to objects at 9 months predicts vocabulary at 12 and 15 months. Developmental Science, 22(1), e12735.

By the end of their first year, most babies begin to talk. A baby’s first word marks one of their biggest milestones. The average baby goes from their first word to 50 words in the course of another year. Fifty words may not seem like a lot, but any parent would tell you that talking is life changing. Something close to miraculous happens during that time, which begs the question: How do babies learn new words?

Most words babies learn within their first year of speaking are nouns. Nouns are learned when a child understands that there is an association between the word a speaker (e.g., a parent) says and the object that the speaker is referring to. During early language acquisition, children make associations when both the child and parent are looking at the same object and the parent labels the object. For example, when a parent says, “Look at the dog,” it is important for the child to direct their attention towards the dog, to make the connection between the spoken word “dog,” and the fuzzy animal their parent is looking at. Whenever the child and parent are attending to an object or event at the same time, developmental scientists call this joint attention. However, some scientists question if joint attention during object naming is the most important factor in early language learning.

Scientists at Indiana University were interested in whether another type of attention, termed sustained attention, might contribute to word learning. Sustained attention refers to the amount of time an infant is able to hold their focus on an object.  Could sustained attention be more important than joint attention for early language learning? To investigate this question, scientist Chen Yu and his colleagues employed eye-tracking technology, which uses a camera to monitor where a child and parent are looking in relation to one another. The scientists placed three objects (e.g., a toy car, train, and cup) between a parent and their 9-month-old infants and let them play as they would naturally. Through eye-tracking, the scientists could measure when and for how long the parent and child looked at the different objects. In addition to measuring child and parent attention, they also recorded instances where the parent labeled objects. The scientists were interested in how these early patterns of attention and object naming between the infant and parent at 9 months of age would relate to how many words the children learn by 12 and 15 months of age.

The researchers found that the ability for infants to sustain their attention on objects while parents were naming them at 9 months of age predicted the size of their vocabulary at 12 and 15 months of age. Specifically, sustained attention during moments of object labeling had a larger contribution to vocabulary growth than did joint attention. Additionally, sustained attention during object labeling predicted vocabulary size regardless of whether or not it occurred along with joint attention. In contrast, joint attention during object naming only contributed to vocabulary growth when it occurred along with sustained attention.

These results significantly shift our understanding of how children learn the names of objects. Many scientists have focused on the importance of joint attention for language development. However, this study found that infants’ ability to share engagement is not as important as their ability to sustain attention towards an object while the parent names it. If a child does not sustain their attention while a parent names an object, these instances do not contribute to vocabulary development.

These results are important for parents and other adults charged with the responsibility of teaching children new words. In particular, following an infant’s attention and naming objects the infant is interested in looking at is more effective at facilitating language development than is attempting to direct the infant’s attention to an object. This approach is especially important for children who have difficulties with attention or language acquisition, such as children with autism, speech delay, or ADHD. The results from this study also support the theoretical basis for many language and behavioral therapies that focus on utilizing child-led behavior as teaching moments.

These results come with an important caveat that it is not always appropriate nor possible for all language learning to be child-directed. Additionally, by preschool, parents should expand beyond labeling objects to encourage further language development. Nevertheless, these results shed light on a baby’s seemingly miraculous transition from “ga-ga-ga,” to “dog.” Next time you interact with an infant of your own or a friend’s, if the baby is interested in the dog while you say, “A dog!”, know that you are helping them learn a new word!

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