Knowing where but not what: impaired thematic roles and spatial language

We describe case J.P. who, following a left inferior frontal lesion, made frequent role confusions in comprehension and production (e.g., saying "The boy kicks the girl" for a picture showing a girl kicking a boy). J.P.'s preserved ability to judge the grammaticality of sentences rules out a syntactic deficit as the primary cause of the role confusions. Thematic role assignment is also required with spatial prepositions such as in or above, and J.P.'s thematic role assignment was also severely impaired with spatial prepositions. We capitalized on prior linguistic analyses and behavioural studies to design accurate tests of the semantics of spatial terms, spatial relations, and critical features of objects. Fine-grain semantic tests revealed that the semantics of spatial terms and objects was intact. We hypothesize that J.P.'s role confusions reflected a failure to integrate objects within semantic representations that define the thematic roles. Our data suggest that properties of objects and thematic roles are specified by distinct semantic processes, which have different brain localizations. J.P.'s lesion further suggests that left inferior frontal regions are critical in thematic role assignment, thus contributing to the understanding of the linguistic functions of these regions.