Differential asymmetries for recognizing nouns and verbs: where are they?

To support categorical representation in the brain for grammatical class, it is necessary to show that noun-verb differences are attributable to parts of speech and not to covarying semantic factors. Prior visual-half field investigations of noun-verb processing have confounded grammatical class with imageability. The current study included numerous tests of differential noun-verb processing across visual fields for stimuli equated for imageability. Task (lexical decision, pronunciation) and list context (blocked vs. mixed lists) variables were examined in 168 right-handed participants. There was no reliable reduction of the right visual field advantage for moderately imageable nouns as compared with verbs. If there are qualitative hemisphere differences in single-word noun and verb recognition, these may be attributable to semantic dimensions that tend to covary with grammatical class.