Abstract
Semantic ambiguity resolution is an essential and frequent part of speech comprehension because many words map onto multiple meanings (e.g., “bark,” “bank”). Neuroimaging research highlights the importance of the left inferior frontal gyrus (LIFG) and the left posterior temporal cortex in this process but the roles they serve in ambiguity resolution are uncertain. One possibility is that both regions are engaged in the processes of semantic reinterpretation that follows incorrect interpretation of an ambiguous word. Here we used fMRI to investigate this hypothesis. 20 native British English monolinguals were scanned whilst listening to sentences that contained an ambiguous word. To induce semantic reinterpretation, the disambiguating information was presented after the ambiguous word and delayed until the end of the sentence (e.g., “the teacher explained that the BARK was going to be very damp”). These sentences were compared to well-matched unambiguous sentences. Supporting the reinterpretation hypothesis, these ambiguous sentences produced more activation in both the LIFG and the left posterior inferior temporal cortex. Importantly, all but one subject showed ambiguity-related peaks within both regions, demonstrating that the group-level results were driven by high inter-subject consistency. Further support came from the finding that activation in both regions was modulated by meaning dominance. Specifically, sentences containing biased ambiguous words, which have one more dominant meaning, produced greater activation than those with balanced ambiguous words, which have two equally frequent meanings. Because the context always supported the less frequent meaning, the biased words require reinterpretation more often than balanced words. This is the first evidence of dominance effects in the spoken modality and provides strong support that frontal and temporal regions support the updating of semantic representations during speech comprehension.
Highlights
Many of the words encountered in everyday language have multiple meanings, which makes the process of mapping word form onto meaning often ambiguous
Cumulative evidence from recent neuroimaging studies has highlighted the importance of two brain areas for semantic ambiguity resolution: the left inferior frontal gyrus (IFG) and the left posterior temporal cortex (Rodd et al, 2005, 2010b, 2012; Davis et al, 2007; Mason and Just, 2007; Zempleni et al, 2007; Bekinschtein et al, 2011)
The results of this study replicate previous findings of increased activation in the left inferior frontal gyrus (LIFG) and posterior temporal cortex for semantically ambiguous sentences compared to unambiguous sentences (Rodd et al, 2005, 2010b, 2012; Davis et al, 2007; Mason and Just, 2007; Zempleni et al, 2007; Bekinschtein et al, 2011)
Summary
Many of the words encountered in everyday language have multiple meanings, which makes the process of mapping word form onto meaning often ambiguous This means that listeners must routinely combine various kinds of contextual information to understand the meaning that is intended by the speaker. To understand the sentence “the woman used a microphone to make the toast,” listeners must use the word “microphone” to understand that the semantically ambiguous word “toast” refers to a celebratory speech rather than grilled bread. Such ambiguity is often not noticed by listeners (Rodd et al, 2005), suggesting that disambiguation is generally a highly efficient and effective process. Psycholinguistic research converges on several cognitive processes that underpin semantic ambiguity resolution: accessing the alternative meanings of an ambiguous word, selecting a single meaning, and reinterpreting that meaning when an incorrect selection is initially made (e.g., Duffy et al, 1988; Gernsbacher, 1991; Simpson, 1994; Twilley and Dixon, 2000; Duffy et al, 2001; Rodd et al, 2010a)
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