A search for the representational content in the putative number form area
Darren Yeo1,2, Courtney Pollack1, Gavin Price1; 1Peabody College, Vanderbilt University, USA, 2Nanyang Technological University, Singapore
Recent studies suggest a putative number form area (NFA) in the inferior temporal gyrus (ITG) that responds preferentially to Arabic numerals versus other symbols. Meta-analytic convergence in the right ITG has been observed for numeral-selectivity (Yeo, Wilkey, & Price, 2017, Neurosci Biobehav Rev., 78, 145-160). However, it is unclear whether the NFA is specialized for processing visual shapes, semantic associations, or both, and whether previous findings depend on actively processing the symbols. Here we use multi-voxel representational similarity (RS) analysis to investigate the functional organization of the NFA during passive viewing of digits, letters, and scrambled digits/letters in 39 adolescents. We tested RS in our data against 5 hypothetical models: (1) pixel- and (2) deformation-based physical shape similarity, (3) symbols versus novel characters, (4) digits versus non-digits, and (5) digits versus letters versus non-symbols. RS across exemplars of the 4 categories in the NFA did not match any of the hypothesized models. As within-category variability may mask potential between-category distinctions, we repeated the analysis using the averaged multi-voxel response pattern to each stimulus category. Results replicated our initial findings. In contrast, RS in the right inferior frontal gyrus matched models 1, 2, & 3. These findings suggest that the NFA, at least during passive viewing, may lack categorical functional organization. This suggests a nuanced role of the putative NFA in category specific digit processing that requires further empirical investigation.
Topic Area: PERCEPTION & ACTION: Vision