Schoolchildren born very preterm are known to present language weaknesses, measured through quantitative tools. However, qualitative aspects of language are less investigated. In the present study, we examined the organization of concepts in verbal memory of very preterm schoolchildren. Using a verbal fluency task, we depicted their semantic network (i.e., the encoding and storage of concepts) and compared it with the semantic network of schoolchildren born at term, based on regular network metrics. Overall, very preterm children shared similar ASPL (i.e., distance between concepts) and Q (i.e., compartmentalization into small sub-networks) than full-term children. However, lower CC (i.e., local interconnectivity) was observed. Here, we discuss this finding through the lens of known processing speed and language use in very preterm children and how pedagogical practices could be seen as a preventive action specifically addressing this issue.
Very preterm schoolchildren are known to have language impairments, impacting semantics, expressive vocabulary, verbal language memory, and grammar10,13. While 12 very preterm children of our cohort were undergoing speech therapy, they overall performed in the norms at the Word Generation subtest. However, they presented subtle difficulties in retrieving information when not organized into categories, with a consequently low comparison score. It may reflect either weaknesses in search strategies due to poorer working memory and inhibition capacity (i.e., executive functions) or a deficit in orthographic fluency or sound awareness. In other words, they have encoded and stored semantic representations in long-term memory and have access to them, but they have not stored orthographic/sound representations or have difficulty retrieving them. However, in terms of categories, very preterm children generated fewer animal names, less unique ones, and poorer diversity compared to the full-term children in the present study. Consequently, if we consider only quantitative measures, we might think that very premature children have vocabulary difficulties and therefore suggest educational support based on learning additional vocabulary. Yet, the underlying difficulties might lie elsewhere. While their global semantic network (ASPL) and vocabulary enrichment (Q) were similar to those of full-term schoolchildren in the present study, the semantic network of very preterm children was less interconnected (CC) than observed in full-term children. Given that less embedded concepts will be harder to be retrieved and used concomitantly with other concepts 17, this qualitative perspective provides new understandings on their linguistic and cognitive difficulties, namely the way they organize and connect information. With a less organized network, it is more difficult to retrieve information. We can observe this difficulty in young childhood, at 18 months, as very preterm infants take more time to respond to spoken demands 43. These authors linked this slowness to the amount of vocabulary the children had independently of their prematurity status. However, it can be hypothesized that this could also be related to the semantic network organization and the difficulty for children to access information. Across development, this may have a cascading effect on learning processes 44. In fact, very preterm children have a lower processing speed in various tasks (e.g., Brydges et al.45). This could reflect an inadequate semantic network organization with the difficulty to relate the information received to known concepts, as well as to retrieve and select concept to respond. Furthermore, while very preterm children show memory impairments in various domains (for a review see Anderson 46), there is evidence that a less interconnected word will be less easily recalled during a memory cued recall task 47. Therefore, their less organized network could be partly responsible for their neurodevelopmental deficits.
Very preterm children are known to experience multisensory difficulties 48,49, that are responsible for higher-level cognitive impairments (for a review see Wallace et al. 50) including language and memory 51. Therefore, their inability to organise new concepts optimally could be explained by multisensory difficulties during the learning process. In view of this vulnerability, it might be appropriate to integrate interventions promoting multi-sensoriality into the learning process. Pedagogies using didactic materials engaging multiple senses, in active-based form, such as the Montessori pedagogy 52, were found to positively impact semantic networks’ structure. Indeed, Montessori schoolchildren compared with traditionally-schooled children, have a higher CC and lower ASPL and Q 24. Therefore, it might be relevant to see pedagogy as a preventive measure for very preterm children. Providing access to educational settings and learning materials that reinforce and train complementary sensory channels will foster qualitative language abilities. Focusing more on meaning and integrating new words while engaging multiple senses rather than teaching isolated concepts, might allow them to build a more interconnected and organized network.
Some limitations need to be acknowledged. First, the experimental settings for the very preterm and full-term children were not similar. For the former, data were collected in the framework of a routine clinical assessment in the context of a longitudinal study, while for the latter, data were collected in the framework of a voluntary-based experiment. Consequently, contexts may not be similarly stressful. Second, bootstrapping in small sample sizes being severely affected by outliers, given our modest sample-size, it was not robust. Nevertheless, our results showed some consistency suggesting that although both groups were small, there did not appear to be issues related to outliers. Yet, it would be relevant to reproduce this study with a bigger cohort to confirm these results. Third, we only evaluated animal-related semantic network. It could be interesting to repeat this task with other semantic categories, such as food or hobbies. In fact, due to its advantages (e.g., generational, cultural, linguistically independent), the semantic category of animals is the most widely used 53. But depending on the child's interest in the category, the organisation of the network may change. Fourth, we acknowledge the non-verbal intelligence measure was not the same for both groups, nevertheless, we took the most similar measure and attested to its validity for the very preterm children. Finally, we only have a cross-sectional perspective. As longitudinal studies show that the clustering coefficient diminishes with age in healthy population 54, it would be interesting to see if it is also the case with very preterm cohorts. In addition, given that very preterm children catch up with some of their weaknesses in adolescence 9,16, we could investigate whether their semantic networks also normalize or follow the same pattern as those of full-term children while keeping these differences.
In conclusion, this study is one of the first to highlight qualitative aspects of language organization of very preterm children compared to full-term children, revealing subtle impairments. In fact, their semantic network appeared to be less connected, probably related to their processing speed and language difficulties. Given the importance of semantic network structure in higher cognitive functions, these findings encourage larger, longitudinal studies in this field. This will lead to improved support and teaching practices for very preterm children.