Characterizing the spatial, functional, and representational properties of the ventral occipitotemporal “Number Form Areas”
Yeo, Darren J.
Arabic digits are perhaps the most ubiquitous symbol set used regardless of one’s native language and script. The ability to read numerals fluently is critical to succeed in the modern world. Yet, we know very little about whether the perceptual system for reading Arabic numerals is the same as that used for reading words. In this dissertation, I present three studies in adults that aimed to characterize the spatial, functional, and representational properties of the putative “Number Form Areas” (NFAs) that are thought to be sensitive to digit shapes and are specialized for processing Arabic numerals. Study 1 searched for the most probable location of an NFA with a coordinate-based meta-analysis of fMRI studies. We found a reproducible region in the right inferior temporal gyrus that responds more to Arabic numerals than to other familiar symbol sets. Study 2 probed whether the candidate right NFA represents information about character category and visual form when digits and other character categories are viewed passively. We found that the right NFA distinguished numerals from other categories, but was not sensitive to digit shapes. These suggest the NFA may be part of a neural pathway for automatic processing of objects with numerical relevance, and that “number form” as a functional label may be inappropriate. Study 3 probed whether the left and right NFAs are functionally different, and whether their functional and representational properties are behaviorally relevant. Our findings suggest that the regions are asymmetrically weighted between hemispheres in some functional responses and representations, but there was no evidence that they are qualitatively different. Individual differences in several properties, including laterality, were also related to symbolic calculation skills. Taken together, the findings not only speak to the existence and properties of the so-called NFAs, but also the interaction between culture and neurobiology – how our brains assimilate or accommodate the learning of multiple culturally defined symbol sets for similar or distinct representational purposes (e.g., words, numbers, and music). This work thus lays the groundwork for understanding the behavioral consequences when a brain struggles to incorporate the learning of different symbol sets within its existing neural architecture.