Impact of moderate prematurity on the ability to learn new words at 18 months” project

The issues

Premature birth can have a considerable impact on the early development of babies. Around 30% of very premature babies (i.e. those born between 28 and 32 weeks’ gestational age) have delays in language acquisition by the age of two. However, we still know too little about language development in moderate to late premature babies (i.e. between 32 and 36 weeks’ gestation). This is particularly important given that moderate to late prematurity accounts for more than 80% of premature births worldwide each year. Therefore, identifying early markers of later language deficits or delays is crucial to better understand the long-term impact of prematurity on cognitive and language functions.

Following our previous work suggesting a speech sound encoding deficit in newborns with moderate prematurity (François et al., 2021), a crucial question addressed in our project is whether moderate to late prematurity negatively impacts associative learning of new words.

Learning minimal pairs, a crucial mechanism for vocabulary acquisition

The ability to build one’s vocabulary is an essential aspect of language acquisition that has been a central topic for modern cognitive neuroscience, both from a developmental and neurocognitive point of view. The emergence of associations between a word and an object, and their storage in memory, are crucial steps that children must take when acquiring their first receptive vocabulary. This ability to make associations is a key learning mechanism, which partly explains the rapid increase in vocabulary in the first two years of life. Another fundamental aspect of optimal lexical development is the ability to distinguish between two words that differ by only one segment, thus forming a minimal pair (such as the words ball and slab).

Project

We used a behavioural paradigm frequently used to measure the learning of new word-object associations at an early age in order to better characterise the impact of prematurity on the development of an essential function of language learning. Specifically, we collected measures of visual fixation time using a small camera hidden above a screen that children looked at during the task of learning new words forming a minimal pair ‘bali’ and ‘pali’.

Our approach and preliminary results

We recruited 18 full-term and 18 moderate to late preterm infants (mean gestational age at birth 33.7 weeks) at 18 months corrected age. After being exposed to the new associations during a learning phase, the children carried out a recognition phase of these associations. To ensure that they were doing the task correctly, the children were asked not only to recognise the new associations but also to recognise familiar associations. While recognition of familiar words was preserved, we observed a negative impact of late to moderate prematurity on recognition of the minimal pair differing by a fine acoustic feature. Specifically, we found that full-term infants recognised the minimal pair well, whereas the preterm group could not. The fact that the preterm infants were unable to learn and recognise the minimal pairs not only confirms previous studies showing that preterm infants may have poor speech processing abilities (François et al., 2021; Paquette et al., 2015), but also suggests that late to moderate prematurity may have a negative impact on associative word learning, particularly when the properties of the stimuli are too constraining. These results provide further evidence for the role that preterm birth may have on the interaction between the perception of subtle phonological difference, early phonetic perception and associative learning mechanisms.

Impact of the project

Despite a rather modest sample size, our results suggest that minimal pair learning can be a useful experimental tool to better understand the impact of premature birth on basic language skills before the emergence of higher cognitive functions during early development. Our results shed light on the critical role that premature birth may have on the interaction between early phonetic perception and the basic associative learning mechanisms required for optimal language development. Furthermore, the study of moderate to late preterm infants is relevant for informing neurodevelopmental models of language processing by providing relevant information on the interaction between early experience and brain maturation.