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Letter processing in the visual system: Different activation patterns for single letters and strings



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Cognitive Affective Behavioral Neuroscience 2005 5 4 452 466 Letter processing in the visual system Different activation patterns for single letters and strings KARIN H JAMES and THOMAS W JAMES Indiana University Bloomington Indiana and GAEL JOBARD ALAN C N WONG and ISABEL GAUTHIER Vanderbilt University Nashville Tennessee One would expect that a lifetime of experience recognizing letters would have an important influence on the visual system Surprisingly there is limited evidence of a specific neural response to letters over visual control stimuli We measured brain activation during a sequential matching task using isolated characters Roman letters digits and Chinese characters and strings of characters We localized the visual word form area VWFA by contrasting the response to pseudowords against that for letter strings but this region did not show any other sign of visual specialization for letters In addition a left fusiform area posterior to the VWFA was selective for letter strings whereas a more anterior left fusiform region showed selectivity for single letters The results of different analyses using both large regions of interest and inspections of individual patterns of response reveal a dissociation between selectivity for letter strings and selectivity for single letters The results suggest that reading experience fine tunes visual representations at different levels of processing An important conclusion is that the processing of nonpronounceable letter strings cannot be assumed to be equivalent to single letter perception Extensive experience with an object class can result in exquisite perceptual skills Car experts can recognize at a glance the makes and models of hundreds of cars and bird watchers can identify the species of a bird briefly seen through foliage The acquisition of such perceptual expertise with objects can lead to functional specialization within the brain systems dedicated to visual processing Faces are commonly used to study the



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