Cross-modal comparisons of stimulus specificity and commonality in phonological processing.

Phonological processing is a fundamental ability which underlies language comprehension. Functional neuroanatomy of phonology constitutes a matter of ongoing debate. In the present study, subjects performed visual (rhyme detection) and auditory (identification of spoken words starting with a given consonant) tasks that were contrasted with matched nonverbal tasks. We identified regions critical for phonological processing which were either stimulus specific or supramodal. The results revealed a high degree of modality specificity in both visual and auditory networks. Moreover, we observed a modality independent region in the left middle temporal gyrus (MTG)/superior temporal sulcus (STS), between a more anterior temporal area with auditory specificity and a more posterior temporal area with visual specificity. This dissociation in functional neuroanatomy suggests that this area may be a core region for supramodal phonological processing, acting as a gateway between spatially separate, but stimulus specific, phonological processes and more general linguistic functions.