An ability to successfully add numerical digits is a key goal of early mathematics education. But the mechanisms by which adults and children develop the skills to perform such arithmetical tasks remain poorly understood. Recently researchers have demonstrated robust evidence that humans have an inbuilt 'number sense' which supports approximate numerical operations. But, to date, the role that this system plays in the development of formal symbolic mathematical skills has been unclear. The project looks at the role of number sense in adults' arithmetic and mathematical performance. In particular the research seeks to determine how number sense interacts with symbolic or verbal representations of number by examining evidence for two competing models of the interaction. Performance on tasks specifically testing number sense skills will be related to performance on more general mathematics tests to reveal the role that number sense has in developing mathematics performance more generally. Furthermore, by using a variety of experiments involving adult participants performing a range of symbolic and nonsymbolic arithmetic tasks, the researchers will investigate the causes for particular characteristics of number sense that are revealed when adults solve arithmetic problems.