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• The findings highlight the semantic relation and grammatical factor in the brain's representation of lexical ambiguities. • Compared to unambiguous words, homonyms and polysemous activate the inferior frontal gyri and posterior temporal region. • Compared to polysemous words, homonyms elicit increased activity in dorsal prefrontal and posterior parietal cortices. • Meanings of homonyms with different syntactic categories are represented distinctively in frontal and temporal cortices. In human languages, it is a common phenomenon for a single word to have multiple meanings. This study used fMRI to investigate how the brain processed different types of lexical ambiguity, and how it differentiated the meanings of ambiguous words. We focused on homonyms and polysemy that differed in the relatedness among multiple meanings. Participants (N = 35) performed a prime-target semantic relatedness task, where a specific meaning of an ambiguous word was primed. Results showed that homonyms elicited greater activation in bilateral dorsal prefrontal and posterior parietal cortices than polysemous words, suggesting that these regions may be more engaged in cognitive control when the meanings of ambiguous words are unrelated. Multivariate pattern analysis further revealed that meanings of homonyms with different syntactic categories were represented differently in the frontal and temporal cortices. The findings highlighted the importance of semantic relations and grammatical factors in the brain's representation of lexical ambiguities. [ABSTRACT FROM AUTHOR]

Phonetic categories have undefined edges, such that individual tokens that belong to different speech sound categories may occupy the same region in acoustic space. In continuous speech, there are multiple sources of top-down information (e.g., lexical, semantic) that help to resolve the identity of an ambiguous phoneme. Of interest is how these top-down constraints interact with ambiguity at the phonetic level. In the current fMRI study, participants passively listened to sentences that varied in semantic predictability and in the amount of naturally-occurring phonetic competition. The left middle frontal gyrus, angular gyrus, and anterior inferior frontal gyrus were sensitive to both semantic predictability and the degree of phonetic competition. Notably, greater phonetic competition within non-predictive contexts resulted in a negatively-graded neural response. We suggest that uncertainty at the phonetic-acoustic level interacts with uncertainty at the semantic level-perhaps due to a failure of the network to construct a coherent meaning. [ABSTRACT FROM AUTHOR]