Auditory processing of different types of pseudo-words: An event-related fMRI study

Imaging results on real word and pseudo-word processing have been heterogeneous, allowing only cautious claims about the neuroanatomical loci of lexico-semantic processing. In order to shed more light on this issue, we examined the impact of different structures of non-lexical stimuli on the outcome of comparisons between such items and matched real words. We anticipated that the degree to which a pseudo-word still resembles a particular real word template determines how word-like it is processed. To verify this idea, we tested different types of pseudo-words (either phonotactically legal and transparently or opaquely derived from real words or phonotactically illegal) in an event-related fMRI paradigm utilizing a lexical decision task. All types of pseudo-words elicited a stronger hemodynamic brain response than real words in the bilateral superior temporal gyri. Real words produced stronger brain activations than pseudo-words in the left posterior middle temporal and angular gyri, the rostral and caudal cingulate gyrus, the precuneus and the right inferior temporal gyrus. When contrasted to opaque pseudo-words transparent pseudo-words elicited a stronger brain response in a temporo-parietal region adjacent to the one observed for real words. Our results provide further support for the involvement of the left posterior middle temporal and angular gyri in lexical–semantic processing. The data also indicate that transparently derived pseudo-words are processed similarly to real words. In contrast, semantic operations are blocked when opaquely derived pseudo-words are processed.