Foreward: Development Is Not About Studying Children: The Importance of Longitudinal Approaches

Abstract

Paradoxically, numerous studies of infants and children are not developmental at all, because they take static snapshots, targeting a specific age group. A truly developmental perspective embraces a developmental way of thinking, regardless of the age of the population studied (Karmiloff-Smith, 1992, 1998). Even research on infants can be nondevelopmental, simply examining performance in, for example, 5-month-olds, whereas some studies of adults are developmental, because they focus on neural change over time in healthy aging even when behavioral output remains unchanged (e.g., Tyler et al., 2009) or on neurodevelopmental disorders as they continue to change in adulthood (Cornish et al., 2008). Indeed, it used to be thought that permutation carriers of the fragile X gene were unimpaired. However, important new research has shown that adult male premutation carriers who have a CGG repeat length of over 100 repeats are at risk of developing a late-onset neurodegenerative condition: fragile X tremor and ataxia syndrome (Cornish et al., 2008; Cornish, Hocking, Moss, & Kogan, 2011). In other words, neural and cognitive development is dynamic across the entire lifespan, and there is no static end state in either healthy adults as they age or in adults with neurodevelopmental disorders.