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Alexandra Coros, Lars Strother, Tutis Vilis; Representation of word parts and wholes in occipitotemporal cortex. Journal of Vision 2013;13(9):1305. doi: https://doi.org/10.1167/13.9.1305.
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We used fMRI to study the cortical representation of words that were split in half between right and left visual hemifields (split at fixation). We measured fMRI responses to words that repeated or changed in one of four possible ways: (1) the whole word repeated; (2) the whole word changed; (3) the left (but not the right) half of the word changed; or (4) the right (but not the left) half of the word changed. We observed substantially decreased fMRI responses to repeated stimuli relative to words that changed (fMRI adaptation) in occipitotemporal cortex (OT), including the ‘visual word form area’ (VWFA) and the ‘occipital face area’ (OFA) in posterior OT. We observed maximal adaptation in the VWFA and bilateral OFA. The VWFA adapted to whole-word repetitions and the OFA adapted to both whole-word repetitions and contralateral half-word repetitions. The exclusive whole-word adaptation effect was unique to the VWFA in left OT; whole-word adaptation was not observed in a putative right OT homologue. Adaptation to contralateral half-word repetitions was maximal in the right OFA and observed to a lesser degree in left OFA. Early visual areas showed equivalent fMRI responses to half-word repetitions. A second experiment showed that, in addition to whole-word adaptation, only the VWFA in left OT showed stronger fMRI responses to four-letter words versus non-word strings of similar retinal size and visual complexity. We conclude that posterior portions of OT represent word parts and the VWFA in left OT represents words as whole units. The VWFA is thus functionally distinct from other more posterior portions of OT that also respond strongly to word stimuli, such as the OFA.
Meeting abstract presented at VSS 2013
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