Dissociating Frontotemporal Contributions to Semantic Ambiguity Resolution in Spoken Sentences

Abstract

Comprehension of sentences containing semantically ambiguous words requires listeners to select appropriate interpretations, maintain linguistic material in working memory, and to reinterpret sentences that have been misinterpreted. All these functions appear to involve frontal cortical regions. Here, we attempt to differentiate these functions by varying the relative timing of an ambiguous word and disambiguating information in spoken sentences. We compare the location, magnitude, and timing of evoked activity using a fast-acquisition semisparse functional magnetic resonance imaging sequence. The left inferior frontal gyrus (LIFG) shows a strong response to sentences that are initially ambiguous (disambiguated by information that occurs either soon after the ambiguity or that is delayed until the end of the sentence). Response profiles indicate that activity, in both anterior and posterior LIFG regions, is triggered both by the ambiguous word and by the subsequent disambiguating information. The LIFG also responds to ambiguities that are preceded by disambiguating context. These results suggest that the LIFG subserves multiple cognitive processes including selecting an appropriate meaning and reinterpreting sentences that have been misparsed. In contrast, the left inferior temporal gyrus responds to the disambiguating information but not to the ambiguous word itself and may be involved in reprocessing sentences that were initially misinterpreted.