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Jessica Cantlon, Melissa Libertus, Elizabeth Brannon, Kevin Pelphrey; The development of abstract numerical processing in parietal cortex. Journal of Vision 2007;7(9):215. doi: 10.1167/7.9.215.
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Functional imaging and lesion studies of adult humans have established a neuro-cognitive link between numerical processing and regions of parietal cortex. Adults with lesions to areas of parietal cortex that encompass the intraparietal sulcus (IPS) exhibit impaired performance on symbolic numerical tasks but not on tasks that test knowledge of other semantic domains (e.g., Dehaene & Cohen, 1991). In addition, functional magnetic resonance imaging (fMRI) studies have revealed number-specific activity in the adult IPS relative to control tasks for non-symbolic numerical values (e.g., Ansari et al., 2006; Cantlon et al., 2006; Piazza et al., 2004). Thus regions of posterior parietal cortex in the adult brain respond to numerical values abstractly, independent of notation.
We tested 7-y-old children and adults as they chose the larger of two numerical values from two visual arrays of dots (non-symbolic condition) or two Arabic numerals (symbolic condition) during an fMRI scan. The numerical comparisons were identical in both conditions and were either easy (0.5 ratio between values) or difficult (0.8 ratio). We examined BOLD activity during the symbolic and non-symbolic conditions as a function of the ratio between the numerical values of the comparisons. Adults exhibited a bilateral ratio effect in posterior parietal cortex whereas children only exhibited this numerical ratio effect in the right hemisphere. The different patterns of brain activity evoked by children and adults may be related to the development of an automatic, symbolic system of numerical representation that has not yet reached maturity by 7 years of age.
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