A Multifactorial Model of Risk for Dyslexia

Thesis (Ph.D.)--University of Washington, 2019There are many competing theories about the causes of dyslexia, a learning disability in which an individual without apparent neurological or circumstantial barriers struggles to become a fluent reader relative to their peers. Many modern hypotheses about dyslexia promote the idea of a “core deficit” originating either in sensory or phonological processes. This dissertation describes four psychophysical studies, both visual and auditory, of children ages 8-12 (n = 205) designed to investigate the claims of various hypotheses about reading disability. We find that indices of categorical behavior on a phoneme labeling task, as well as summary measures of performance on a random dot motion discrimination task, are correlated with reading skill. However, effect sizes and patterns of correlations between multiple predictors of reading skill do not support the framework of a core deficit in either sensory or phonological processes. Instead, results are consistent with an additive risk factor model, in which several distinct causal pathways are required to explain variance in reading skill at the population level