Taylor, J. 1 , Rastle, K. 2 & Davis, M. 1
1 MRC Cognition and Brain Sciences Unit, Cambridge, UK
2 Royal Holloway University of London, UK
Dehaene and colleagues propose that the left fusiform gyrus (LFG) contains a specialised visual word form area (VWFA) representing abstract orthographic units. Conversely, Price and others argue that the LFG processes both visual objects and words, attributing word-specific responses to task-related top-down modulation. We combine an artificial language paradigm with fMRI, providing a unique opportunity to explore ventral-temporal specialisation whilst learning novel words and objects. Examining learning maximises task differences: words must be decoded using systematic spelling-sound mappings whereas objects must be arbitrarily associated with their names. Twenty healthy adults learned new names for 24 novel objects and to read 24 new words written in novel symbols, whilst in an MRI scanner. Learning consisted of interleaved phases of training (paired visual-spoken forms) and testing (read words/name objects). Participants learned the trained items (words-69%, objects-68% correct) and generalized their orthographic knowledge to untrained words (62% correct). Relative to unimodal listening/viewing, cross-modal associative learning of visual-spoken form pairings activated bilateral superior parietal cortices, fusiform gyri and left hippocampus (p<.01 whole-brain corrected). These regions active for learning objects and words were used as a search volume for subsequent analyses. The LFG (including VWFA) was more active when learning object-name associations than when learning to read words. The reverse contrast revealed activation in bilateral superior parietal cortices. During a final test phase, covert word reading versus object naming showed the same patterns of dissociation in LFG and superior parietal areas, with additional activation for words compared to objects in a left mid-occipital region previously associated with pseudoword reading. The weaker involvement of the LFG in orthographic relative to object-label learning perhaps challenges the idea that this region is specialised for reading. Conversely, strong involvement of parietal regions in orthographic learning suggests a focus for future neuroimaging research on leanring to read.