study of cognitive development. Specifically, various measures of speed of processing were used to examine changes in the speed of information processing as a function of age. Kail (1991) showed that speed of processing increases exponentially from early childhood to early adulthood. Studies of RTs in young children of various ages are consistent with common observations of children engaged in activities not typically associated with chronometry. This includes speed of counting, reaching for things, repeating words, and other developing vocal and motor skills that develop quickly in growing children. Once reaching early maturity, there is then a long period of stability until speed of processing begins declining from middle age to senility (Salthouse, 2000). In fact, cognitive slowing is considered a good index of broader changes in the functioning of the brain and intelligence. Demetriou and colleagues, using various methods of measuring speed of processing, showed that it is closely associated with changes in working memory and thought (Demetriou, Mouyi, & Spanoudis, 2009). These relations are extensively discussed in the neo-Piagetian theories of cognitive development. During senescence, RT deteriorates (as does fluid intelligence), and this deterioration is systematically associated with changes in many other cognitive processes, such as executive functions, working memory, and inferential processes. In the theory of Andreas Demetriou, one of the neo-Piagetian theories of cognitive development, change in speed of processing with age, as indicated by decreasing RT, is one of the pivotal factors of cognitive development. Health and mortality Performance on simple and choice reaction time tasks is associated with a variety of health-related outcomes, including general, objective health composites as well as specific measures like cardiorespiratory integrity. The association between IQ and earlier all-cause mortality has been found to be chiefly mediated by a measure of reaction time. These studies generally find that faster and more accurate responses to reaction time tasks are associated with better health outcomes and longer lifespan. Big-Five personality traits Although a comprehensive study of personality traits and reaction time has yet to be conducted, several researchers have reported associations between RT and the Big Five personality factors of Extraversion and Neuroticism. While many of these studies suffer from low sample sizes (generally fewer than 200 individuals), their results are summarized here in brief along with the authors' proposed biologically-plausible mechanisms. A 2014 study measured choice RT in a sample of 63 high and 63 low Extraversion participants, and found that