Poster C140, Sunday, March 26, 5:00 – 7:00 pm, Pacific Concourse
Overlapping neural representations of magnitude support understanding nonsymbolic and symbolic fractions
John Binzak1, Elizabeth Toomarian1, Edward Hubbard1; 1University of Wisconsin - Madison
A fundamental question in numerical cognition is how we retrieve the meaning of number symbols-the “symbol grounding problem”. To address the symbol grounding problem for fractions, 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 the RPS provides an underappreciated neurocognitive startup tool upon which the meaning of symbolic fractions (e.g. ¾) can be built. Although previous studies have demonstrated that the intraparietal sulcus (IPS) and prefrontal cortex (PFC) are involved in processing nonsymbolic ratios and symbolic fractions, no experiment has directly compared activation for these two classes of stimuli in the same participants. We tested the hypothesis that processing of symbolic fractions builds on the RPS by having adults compare the magnitudes of two fractions in three conditions: pairs of symbolic fractions, line ratios, or mixed line-fraction. Distance effects were observed in all three conditions; participants were faster and more accurate as the numerical distance between pairs increased. Additionally, participants were faster and more accurate to compare line ratios than either condition containing symbolic fractions. Critically, activation of the bilateral IPS overlapped for all three conditions, with fMRI activation closely paralleling RT distance effects. We found greater activation when numerical distances were small compared to when they were close. These results suggest that the processing of symbolic fractions and nonsymbolic ratios rely on similar neural regions sensitive to ratio magnitudes, consistent with the RPS account.
Topic Area: THINKING: Reasoning