The Changing Roles of the Language and Attention Systems in Statistical Learning across Development

Statistical learning (SL), the ability to detect and extract regularities from inputs, has been considered as an early-maturing and domain-general mechanism that is critical for typical language development. However, recent evidence in neurotypical adults and children have found that individuals can vary in their SL abilities across linguistic and nonlinguistic domains as well as across auditory and visual modalities. Moreover, rather than being developmentally stable, SL was found to improve with age in the nonlinguistic domain, while mixed evidence has been found in the linguistic domain. A substantial gap still exists in our understanding of how SL in the linguistic domain changes across development and across individuals with different levels of language experience. This dissertation aimed to understand a). how SL develops across linguistic and nonlinguistic domains in neurotypical adults and children, b) whether SL can serve as a predictor of language development in children with language difficulties, c). how domain-general attention system is engaged during SL in typical development, and d). whether domain-general attention can facilitate SL in children with language difficulties. Chapter 2 to 3 revealed that neurotypical children demonstrated a strikingly faster learning rate and greater learning-induced neuroplasticity in the language network during linguistic SL when compared to neurotypical adults. Chapter 4 showed that autistic children who have heterogenous language skills exhibit specific impairment in linguistic SL, while their nonlinguistic SL was comparable to neurotypical children. A potential reciprocal relationship was found between linguistic SL and language development in autistic children. Chapter 2 - 4 highlighted that linguistic SL varies across development. The plasticity of the language network and the amount of accumulated language exposure of the learners could both determine the outcomes of linguistic SL. Given the unique role of linguistic SL in language development, it is important to understand factors that can facilitate linguistic SL across development. Attention is a late-maturing and domain-general cognitive function that supports learning across domains and development. However, clarifying the role of attention in SL remains an area of ongoing research. It remains unknown how attention is engaged during linguistic SL across development. To answer this question, Chapter 5 Study 1 showed that neurotypical children showed a significantly greater learning-induced change than adults in both the dorsal attention network and the language network during auditory linguistic SL. During the later stage of learning, neurotypical children also showed a significantly stronger change towards anticorrelation between the dorsal attention network and the language network compared to adults. These findings highlighted a changing relationship between the attention and language network during linguistic SL across development. The greater short-term plasticity observed in children compared to adults in both networks might confer an advantage for children in learning regularities from new linguistic inputs. Chapter 5 Study 2 further revealed that orienting children's attention to specific stimuli during the learning process facilitated linguistic SL across neurotypical children, autistic children, and non-autistic children with reading difficulties. The ability to learn statistical patterns from attended visual linguistic inputs predicted gains of emergent literacy skills in a reading intervention, and improved literacy skills, in turn, enhanced SL capacities in children with reading difficulties. These findings together suggested that through its interaction with both the language network and language experiences, attention plays a crucial role in modulating linguistic SL, which in turn, shapes language development across populations with varying neurodevelopmental trajectories. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]