REGIONAL CEREBRAL BLOOD-FLOW DURING OBJECT NAMING AND WORD READING

By several accounts, reading single words may be accomplished either b y sequentially transcribing orthographic units into their correspondin g sounds (an indirect route), or by directly associating a visual word form to the semantic or articulatory representation (a direct route). By contrast, the similar task of naming objects must rely only on a d irect route, since objects cannot be ''sounded out.'' To study the loc alization of cognitive processes specific to reading, we used positron emission tomography (PET) to measure regional cerebral blood flow whi le subjects named words and pictures of objects silently or aloud. Gro up averages of blood now changes were obtained for experimental vs. co ntrol tasks. Object and word presentations elicited similar blood now increases in extra-striate visual cortices compared with a visual nois e control. Silent reading invoked a neural network very similar to tha t seen when subjects named objects silently, consistent with a ''direc t'' route. Naming objects aloud produced the addition of motor output regions to this network By contrast, oral reading produced a markedly different pattern of activated regions, suggesting reliance on a separ ate phonological pathway. These results provide support for the dual c oding hypothesis in reading and challenge the use of strict hierarchic al models of cognitive operations in PET activation studies. (C) 1995 Wiley-Liss, Inc