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Correspondence between cognitive and neural representations for phonology, orthography, and semantics in supramarginal compared to angular gyrus
Poster A25 in Poster Session A, Thursday, October 6, 10:15 am - 12:00 pm EDT, Millennium Hall
William Graves1, Jeremy Purcell2, David Rothlein3, Donald Bolger2, Miriam Rosenberg-Lee1, Ryan Staples1; 1Rutgers University, 2University of Maryland, 3VA Boston Healthcare System
The angular and supramarginal gyri (AG and SMG) roughly correspond to Brodmann areas 40 and 39, and von Economo areas PF and PG. Together they constitute the inferior parietal lobule (IPL) and have been associated with cognitive functions that support reading. How those functions are distributed across the AG and SMG is a matter of debate, the resolution of which is hampered by inconsistencies across stereotactic atlases provided by the major brain image analysis software packages. Schematic results from tools that automate meta-analyses suggest primarily semantic (word meaning) processing in the left AG, with more spatial overlap among phonological (auditory word form), orthographic (visual word form), and semantic processing in the left SMG. To systematically test for correspondence among patterns of neural activation and phonological, orthographic, and semantic representations, we re-analyzed a functional magnetic resonance imaging dataset of participants reading aloud 465 words. Using representational similarity analysis, we tested the hypothesis that within cytoarchitecture-defined subregions of the IPL, phonological representations are primarily associated with the SMG, while semantic representations are primarily associated with the AG. To the extent that orthographic representations can be de-correlated from phonological representations, we hypothesized that they would be associated with cortex peripheral to the IPL, such as the intraparietal sulcus. Semantic representations were quantified using the Global Vectors for Word Representation model, which learns co-occurrence based embeddings from a large corpus of text. While the relationship between semantic and orthographic or phonological representations is nearly arbitrary and therefore uncorrelated, investigating orthographic and phonological representations is more challenging. To that end, we defined orthographic and phonological dissimilarity in terms of string edit distance, but for phonology we included phonetic features corresponding to place and manner of articulation. Results largely confirmed our hypotheses, with both ROI and searchlight analyses showing neural correspondence with semantic representations primarily in left AG, phonology in left SMG, and orthography outside but adjacent to the IPL in the intraparietal sulcus and nearby superior parietal lobule. Comparing these results to computational models of reading that also specify the relevant representations, we note that, contrary to models that do not implement semantic representations, the results are more consistent with neurally inspired computational cognitive models of reading that learn mappings among distributed representations for orthography, phonology, and semantics. Overall, our results lend new clarity to the spatial organization of reading-related cognitive representations within the left IPL. This additional precision was achieved through careful selection of word stimuli and representational formats to aid in using partial correlation RSA for localizing orthographic, phonological, and semantic representations. On the neural side, cytoarchitecture-based segmentations were used to distinguish PF/SMG from PG/AG in a way that largely agreed with landmark-based atlases. We propose this approach as a roadmap for achieving additional cognitive and neural precision in future cognitive neuroscience investigations.
Topic Areas: Speech Motor Control, Methods