A parametric approach to orthographic processing in the brain: An fMRI study

Brain activation studies of orthographic stimuli typically start with the p remise that different types of orthographic strings (e.g., words, pseudowor ds) differ from each other in discrete ways, which should be reflected in s eparate and distinct areas of brain activation. The present study starts fr om a different premise: Words, pseudowords, letterstrings, and false fonts vary systematically across a continuous dimension of familiarity to English readers. Using a one-back matching task to force encoding of the stimuli, the four types of stimuli were visually presented to healthy adult subjects while fMRI activations were obtained. Data analysis focused on parametric comparisons of fMRI activation sites. We did not find any region that was e xclusively activated for real words. Rather, differences among these string types were mainly expressed as graded changes in the balance of activation s among the regions. Our results suggest that there is a widespread network of brain regions that form a common network for the processing of all orth ographic string types.