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Abstract:
Event-related fMRI was used to investigate lexical
decisions to words of high and low frequency of occurrence
and to pseudowords. The results obtained strongly support
dual-route models of visual word processing. By contrasting
words with pseudowords, bilateral occipito-temporal brain
areas and posterior left middle temporal gyrus (MTG) were
identified as contributing to the successful mapping of
orthographic percepts onto visual word form representa-
tions. Low-frequency words and pseudowords elicited
greater activations than high-frequency words in the
superior pars opercularis [Brodmann’s area (BA) 44] of
the left inferior frontal gyrus (IFG), in the anterior insula,
and in the thalamus and caudate nucleus. As processing of
these stimuli during lexical search is known to rely on
phonological information, it is concluded that these brain
regions are involved in grapheme-to-phoneme conversion.
Activation in the pars triangularis (BA 45) of the left IFG
was observed only for low-frequency words. It is proposed
that this region is involved in processes of lexical
selection.
