The Neural Time Course of Semantic Ambiguity Resolution in Speech Comprehension

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.

The relationship between sentence comprehension and lexical-semantic retuning

“…Word-meaning priming seems to operate on the output of good-enough processing: for lower frequency meanings of ambiguous words, a subsequent context may not be enough to easily repair an initial misinterpretation, whereas for prior disambiguation sentences, the ambiguity is more easily resolved and priming occurs more reliably. This is supported by brain imaging studies showing differences in fMRI bold responses and event-related potentials for subsequent disambiguation sentences that resolve to a subordinate meaning, which presumably reflects the detection of misinterpretation and/or effortful repair process (Macgregor et al, 2020;Rodd et al, 2012). More generally, the effect of the probe task on sentence processing underscores the importance of conceptual replications for investigating the phenomenon of interest separate from any potential task-specific effects.…”

“…In most cases, these constraints will support the selection of the correct meaning. However, occasionally the listener/reader will select the wrong meaning of a word and correct comprehension will depend on subsequently detecting that error and engaging in a cognitively demanding reinterpretation process (Macgregor et al, 2020;Rodd, Johnsrude, & Davis, 2010).…”

“…The repair processes that occur during subsequent disambiguation sentences may similarly signal that the current representations are not optimally supporting comprehension. Indeed, brain imaging data suggest that there is a large processing cost when these types of sentences resolve to a subordinate meaning, compared to when they resolve to a dominant meaning or remain unresolved, which is likely due to an effortful search for alternative word meanings and sentence re-evaluation (Macgregor et al, 2020;Rodd, Johnsrude, & Davis, 2012). Given that word-meaning priming has already been observed using prior disambiguation sentences (Betts et al, 2018;Gaskell et al, 2019;Gilbert et al, 2018;Rodd et al, 2016Rodd et al, , 2013, this account must predict that some degree of learning occurs automatically in response to all ambiguous words.…”

Listening Effort Is Not the Same as Speech Intelligibility Score

“…The increased effort likely reflects the cost of overcoming the initial automatic predictions generated from the misperceived words ( Shenhav et al., 2017 ). There are entire paradigms of research based on the concept of building and then intentionally violating a listener’s expectations to demonstrate the influence of language on predictive and restorative processing ( Kutas & Hillyard, 1984 ), including studies that track the resolution of sentence structure in real time ( MacGregor et al., 2019 ). The study of speech perception by individuals with hearing impairment offers a special opportunity to observe the consequences of these predictions and violations while still using typical sentences that have the desirable quality of maintaining the listener’s normal expectation of coherent sensible stimuli.…”

Listening effort is not the same as speech intelligibility score

“…This concept hinges on the notion that listeners expect a sentence to make sense, and will employ extra effort to re-parse the sentence when it is not sensible. There are entire paradigms of research based on the concept of building and then intentionally violating a listener's expectations in order to demonstrate the influence of language on predictive and restorative processing (Kutas & Hillyard 1986), including studies that track the resolution of sentence structure in real time (MacGregor et al 2019). The study of speech perception by individuals with hearing impairment offers a special opportunity to observe the consequences of these predictions and violations while still using typical sentences which have the desirable quality of maintaining the listener's normal disposition of expecting sensible stimuli.…”