Nature and Nurture in Numerical Cognition : Investigating the Idea of a Generalized Magnitude System for Number, Space, and Time

Current research in the field of numerical cognition reveals strong behavioral interactions and similar processing mechanisms for the perceptions of space, time, and number; which is generally believed to indicate that these dimensions share a common metric for representation in the brain. These three dimensions of magnitude––analog, ratio dependent representations of space, time, and number––are essential for interaction with the environment, and provide a conceptual basis on which further perceptual experience enhances the discrimination of distance, speed, numerosity, quantity, and size. Basic, approximate and non-verbal conceptions of spatial navigation, temporal orienting, and numerical computations have been found in human adults and children, as well as non-human animals, while the employment of discrete measures seems to be a consequence of a verbally and culturally mediated ontogenetic shift exclusive to humans (e.g. Feigenson, Libertus, and Halberda, 2013). This thesis investigates the link between nature and nurture, in an attempt to find the key factor that ultimately induces the ontogenetic shift from approximate to exact representations of space, time, and number. An extensive theoretical review is performed, based on both neuroscientific and cross-cultural data, where I propose that cultural and linguistic mediation is as vital to the representational advancement of numerical cognition as our biologically predisposed magnitude system. The neuroscientific approach is strongly based on a leading––but controversial––theory in the field of numerical cognition, ATOM (Walsh, 2003), which suggests that both human and non-human animals possess a generalized magnitude system with fully shared representational mechanisms for space, time, and number. To further illustrate the assumed theoretical stance of ATOM, an exploratory fMRI study with a single participant is performed, with results closely resembling those argued by Walsh (2003).