A University of Oslo study finds no evidence that parents adjust their speech to highlight words infants do not know. Baby talk may serve other purposes.
When speaking to infants, parents often use a high-pitched voice, slower tempo, and clearer articulation. This so-called infant-directed speech, also referred to as ‘baby talk’, is thought to support early language development. But is it also used deliberately by parents to teach individual words? A new study published in Developmental Psychology suggests the answer is no.

– We expected parents to exaggerate their pronunciation of words their infant did not know, in order to support learning. We found no evidence that this happens, says Audun Rosslund, first author of the study.

Not a teaching strategy
In the study, Norwegian parents read a picture book containing words such as car, pig, and cake to their infants, who were between 8 and 18 months old. Parents were also asked to evaluate each word: Did their infant understand it? Could their infant say it? Or was it unknown?

Recordings were made while parents read the book both to their infant and to another adult (as a control condition). From these recordings, researchers extracted more than 38,000 vowels from the words. They then analyzed parents’ pitch, pitch variation (the ‘ups and downs’), duration, and clarity of pronunciation, based on the infants’ presumed knowledge of each word, according to their parent.

– Our results suggest that parents do not change the acoustic features of words depending on whether they think their infant knows them or not. So, during shared book reading, infant-directed speech does not appear to be used as a didactic strategy for teaching individual words. This doesn’t mean this type of speech isn’t useful for language development, but it seems to serve other functions, such as maintaining the child’s attention, and foster social and emotional connection, says Rosslund.
Important addition to previous research
This is the first time researchers have studied how words are pronounced in relation to word knowledge in such young children. The new findings do not support the idea of targeted adjustments in pronunciation.

– In fact, we saw tendencies in the opposite direction: Parents sometimes exaggerated their pronunciation more for words they believed the child already knew. This may reflect joy, engagement, or a way of reinforcing what the child has already learned, says Rosslund.

A broader role for infant-directed speech
The findings support an alternative view of infant-directed speech: Rather than being a tool for teaching individual words, it may primarily have social and emotional functions in early communication.

– Infant-directed speech can still be important for language development at this age, but perhaps in more indirect ways, by fostering interaction, bonding, and shared attention, Rosslund explains.

A lost opportunity?
The fact that parents do not adjust their pronunciation according to their infants’ word knowledge does not necessarily mean that such adjustments would have no positive effect. On the contrary, the findings raise new questions: Could deliberate use of clearer pronunciation be a low-threshold intervention to support word learning, especially in children with delayed language development?

– Our study cannot answer that, but it does highlight a potential for future research, says Rosslund.