Abstract
Semantically ambiguous words challenge speech comprehension, particularly when listeners must select a less frequent (subordinate) meaning at disambiguation. Using combined magnetoencephalography (MEG) and EEG, we measured neural responses associated with distinct cognitive operations during semantic ambiguity resolution in spoken sentences: (i) initial activation and selection of meanings in response to an ambiguous word and (ii) sentence reinterpretation in response to subsequent disambiguation to a subordinate meaning. Ambiguous words elicited an increased neural response approximately 400-800 msec after their acoustic offset compared with unambiguous control words in left frontotemporal MEG sensors, corresponding to sources in bilateral frontotemporal brain regions. This response may reflect increased demands on processes by which multiple alternative meanings are activated and maintained until later selection. Disambiguating words heard after an ambiguous word were associated with marginally increased neural activity over bilateral temporal MEG sensors and a central cluster of EEG electrodes, which localized to similar bilateral frontal and left temporal regions. This later neural response may reflect effortful semantic integration or elicitation of prediction errors that guide reinterpretation of previously selected word meanings. Across participants, the amplitude of the ambiguity response showed a marginal positive correlation with comprehension scores, suggesting that sentence comprehension benefits from additional processing around the time of an ambiguous word. Better comprehenders may have increased availability of subordinate meanings, perhaps due to higher quality lexical representations and reflected in a positive correlation between vocabulary size and comprehension success.
Highlights
Most common words are semantically ambiguous, such that their meaning depends on context
Using MEG/EEG, we investigated the spatiotemporal dynamics of semantic ambiguity resolution by recording neural responses time-locked to the offset of an ambiguous word and to a subsequent disambiguating word that resolved the ambiguity to a subordinate meaning
Neural activity after an ambiguous word reflects the activation of multiple alternative interpretations in a representational space that provides a mechanism for meaning maintenance such that subsequent context can guide selection
Summary
Most common words are semantically ambiguous (for a review, see Rodd, Gaskell, & Marslen-Wilson, 2002), such that their meaning depends on context. When listeners (or readers) encounter an ambiguous word (e.g., “ace”), semantic priming studies suggest that they automatically activate the multiple meanings of that word in parallel (irrespective of context) but, within a few hundred milliseconds, settle on a single preferred meaning (Seidenberg, Tanenhaus, Leiman, & Bienkowski, 1982; Swinney, 1979). Initial meaning selection operates on the information available at that time (Cai et al, 2017; Rodd, Cutrin, Kirsch, Millar, & Davis, 2013; Duffy, Morris, & Rayner, 1988; for a review, see Vitello & Rodd, 2015), which will be challenging if disambiguating context is absent or delayed until after the ambiguous word. If a subsequent context supports a subordinate (less frequent, more unexpected) meaning, a later process of reinterpretation is often necessary for accurate comprehension
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