Abstract
Adult humans, human infants, pre-school children, and non-human animals appear to share a system of approximate numerical processing for non-symbolic stimuli such as arrays of dots or sequences of tones. Behavioral studies of adult subjects implicate a link between these non-symbolic numerical abilities and symbolic numerical processing in humans however, neuroimaging studies have remained inconclusive on the neural basis of this link. The intraparietal sulcus (IPS) is known to selectively respond to symbolic numerical stimuli such as Arabic numerals (see Dehaene et al., 2003 for review) however, two recent studies have arrived at opposite conclusions regarding the role of the IPS in processing non-symbolic, numerosity arrays (Piazza et al., 2004; Shuman & Kanwisher, 2004). Using functional magnetic resonance imaging (fMRI) at 4-Tesla and an event-related adaptation paradigm, we found that adult subjects showed a greater IPS response to visual arrays that deviated from standard stimuli in their number of elements than to stimuli that deviated from standards in local element shape. These results suggest a neurophysiological link between non-symbolic and symbolic numerical processing in adulthood. We hypothesized that the IPS may also be an important substrate for numerical processing early in human development, before sophisticated symbolic numerical skills develop (e.g., Spelke, 2002). We tested four-year-old children with the same fMRI-adaptation paradigm as adult subjects and found that the IPS responded to numerical deviants similarly in four-year-old children and adults. Thus the fundamental substrate of numerical cognition appears to be present early in development.