A supramodal brain substrate of word form processing--an fMRI study on homonym finding with auditory and visual input.

Homonym processing in German is of theoretical interest as homonyms specifically involve word form information. In a previous study (Weis et al., 2001), we found inferior parietal activation as a correlate of successfully finding a homonym from written stimuli. The present study tries to clarify the underlying mechanism and to examine to what extend the previous homonym effect is dependent on visual in contrast to auditory input modality. 18 healthy subjects were examined using an event-related functional magnetic resonance imaging paradigm. Participants had to find and articulate a homonym in relation to two spoken or written words. A semantic-lexical task - oral naming from two-word definitions - was used as a control condition. When comparing brain activation for solved homonym trials to both brain activation for unsolved homonyms and solved definition trials we obtained two activations patterns, which characterised both auditory and visual processing. Semantic-lexical processing was related to bilateral inferior frontal activation, whereas left inferior parietal activation was associated with finding the correct homonym. As the inferior parietal activation during successful access to the word form of a homonym was independent of input modality, it might be the substrate of access to word form knowledge.