Neurocognitive Relationships between Nonsymbolic and Symbolic Ratio Processing in Children and Adults
John V. Binzak1, Yunji Park1, Elizabeth Y. Toomarian1, Priya B. Kalra1, Yun-Shiuan Chuang1, Percival G. Matthews1, Edward M. Hubbard1; 1University of Wisconsin--Madison
Based on findings from neuroscience and educational research, we have recently argued that the brain contains a ratio processing system (RPS) adapted to perceiving nonsymbolic ratios (e.g. the ratio of two line lengths; Lewis, Matthews & Hubbard, 2015), and that this RPS provides an underappreciated neurocognitive startup tool upon which the meaning of symbolic fractions (e.g. ¾) can be built (Matthews, Lewis & Hubbard, 2016). To further test the hypothesis that processing symbolic fractions builds on the RPS, we collected behavioral and fMRI data in three groups of participants (adults, 2nd grade children and 5th grade children) while they made a series of magnitude judgments in three conditions: symbolic fractions, line ratios, or mixed pairs. Although previous fMRI studies have examined symbolic and nonsymbolic ratio processing separately, no study has measured both in the same participants nor contrasted how they change with development. In each group, participants were faster and more accurate as the numerical distance between pairs increased, and were faster for nonsymbolic ratio judgments than either condition containing symbolic fractions. Neural distance effects were observed in bilateral intraparietal sulcus (IPS), prefrontal cortex (PFC) and occipital-temporal cortex. Adults relative to children showed greater overlap in bilateral IPS and PFC for symbolic and nonsymbolic judgments, suggesting that these regions become specialized to support magnitude processing with ratios regardless of format. Additionally, 5th grade children, relative to 2nd graders, showed greater distance effects (stronger negative slope) in the IPS, indicating that specialization of these regions occurs during early formal math instruction.
Topic Area: THINKING: Reasoning