Many dimensions of perceptual and cognitive development, including establishing the ability to understand and manipulate speech sounds, occur along a consistent and normative trajectory for most children. Canalization, or the protection from developmental events that may perturb normal development, has long been hypothesized to explain normative biological development. In large samples of children and adults, we demonstrated that asymmetrical development of brain structure may explain normative phonological development, an ability that is a building block for learning to read. People with the most extreme brain structure asymmetries, including in frontal cortex linked to decision-making, exhibited average phonological ability whereas those with less or no asymmetry exhibited atypically worse or better phonological ability that the rest of the sample. Thus, cortical asymmetries may help to ensure normal phonological development.
