Exploring the interplay of sleep, memory and development in infancy: a holistic perspective on vocabulary learning

This PhD thesis by articles investigates the associations between sleep, memory processes, motor skill, and vocabulary growth in infancy. The underlying theoretical framework on child development is holistic; It conceptualises vocabulary learning as related to memory and as resulting from the interaction between the body and the environment. The goal is to provide a biologically grounded understanding of how phonological and lexical networks are built. The first article reviews research on the associations between sleep and word learning during infancy. In 16 identified papers, positive associations between sleep and several aspects of word learning are revealed. Moreover, the studies show associations between the sleeping brain activity and word learning, long-term effects of infant sleeping habits on vocabulary development and relationships between the child’s existing knowledge and the consolidation of linguistic information post-sleep. The second article further examines the role of sleep in language development by focusing on word form generalisation, showing that the combination of a post-encoding nap with nocturnal sleep significantly supports it. These findings clarify the relative importance of naps and nighttime sleep for phonological development. The third article investigates the associations between the evolution of sleep patterns, motor skills progression and vocabulary growth over the first two years. It shows nonlinear associations among these domains, emphasising their emergence at ages of sharp developmental change. This study highlights the necessity of adopting a dynamic systems perspective to comprehend vocabulary growth as the product of continuous interactions between cognition, the body, and the environment. Together, these articles illuminate early lexical development by examining it in relation to memory processes and its connections with motor development. They highlight that the developmental changes observed in the domains of communication, locomotion and sleep regulation are mutually intertwined and rely on shared memory processes and on interactions between the child and their surroundings.