Environmental influences on communication development: Implications for children with neurodevelopmental communication impairments

At the intersection of clinical neuroscience and communication sciences and disorders, this dissertation provides a compilation of studies aimed at examining contextual influences on children's communication development and the implications of this work for children with neurodevelopmental communication impairments. As discussed in Chapter 1, the present work is grounded in dynamic systems theory of development and a distributed model of communication, which together emphasize development as a context-dependent dynamic multilevel system that unfolds over time and is shaped by a multitude of factors. Neurodevelopmental communication impairments such as speech sound disorder, language disorder, and autism spectrum disorder affect approximately 1.5 - 16% of children, and are associated with academic, socioemotional, and behavioral difficulties. The work in Chapter 2 directly examines a common form of environmental support for children with neurodevelopmental communication impairments, speech-language therapy. More specifically, it assesses the effectiveness of a multimodal, integrated speech-language intervention in facilitating multisyllabic productions in six children 2-4 years of age with various neurodevelopmental disabilities. It uses single-case and within-subject experimental designs to understand individual trajectories and shape clinical practice. As a complement to the behavioral intervention, Chapter 3 of this thesis explores the novel use of noninvasive biosensors to measure electrical conductance across the skin during speech-language and occupational therapy as a potential support for communication in eight children, ages 2-11, with neurodevelopmental disabilities. Skin conductance is mediated by sympathetic cholinergic sudomotor nerve fibers and has been used extensively in the study of psychological states and processes. However, traditionally its use has been limited to highly controlled laboratory settings, whereas the use of such technology within the context of daily activities remains a major challenge. Next, as a means to examine a broader range of environmental influences, Chapter 4 uses a longitudinal monozygotic (MZ) twin difference method, a genetically sensitive design, to examine four candidate nonshared environmental influences on children's language development: birthweight, breastfeeding, and home reading exposure and parenting (M age = 7). This study aims to identify nonshared environmental effects on later language development, at mean ages 10 (n = 115 pairs) and 12 years (n = 108 pairs), across two assessment contexts: standardized testing and narrative language sampling. Finally, Chapter 5 concludes this dissertation by highlighting the need to study a broader range of contextual factors influencing communication development and its associated mechanisms, incorporate diverse and complementary methodologies, and develop effective communication supports for children with neurodevelopmental communication impairments