Lexical decision of nonwords and pseudowords in humans: a positron emission tomography study

In this functional positron emission tomography study brain activations during an auditory lexical decision task with two experimental conditions were investigated. First, the subjects had to discriminate between real words and nonwords; second, real words varied with pseudowords. Comparing each of these tasks to an auditory control condition we found bilateral activation of the superior temporal and inferior frontal gyrus, lateralized to the left in the pseudoword condition. The comparison of the lexical decision tasks revealed higher rCBF during the pseudo-/real word decisions within BA 47, adjacent to Broca's area, and the anterior cingulate. The data support the notion that the lexical decision during a nonword task is mainly based on a phonological discrimination process, whereas a pseudoword task more strongly requires lexical access resulting in activation of BA 47.