Abstract
Under adverse listening conditions, prior linguistic knowledge about the form (i.e., phonology) and meaning (i.e., semantics) help us to predict what an interlocutor is about to say. Previous research has shown that accurate predictions of incoming speech increase speech intelligibility, and that semantic predictions enhance the perceptual clarity of degraded speech even when exact phonological predictions are possible. In addition, working memory (WM) is thought to have specific influence over anticipatory mechanisms by actively maintaining and updating the relevance of predicted vs. unpredicted speech inputs. However, the relative impact on speech processing of deviations from expectations related to form and meaning is incompletely understood. Here, we use MEG to investigate the cortical temporal processing of deviations from the expected form and meaning of final words during sentence processing. Our overall aim was to observe how deviations from the expected form and meaning modulate cortical speech processing under adverse listening conditions and investigate the degree to which this is associated with WM capacity. Results indicated that different types of deviations are processed differently in the auditory N400 and Mismatch Negativity (MMN) components. In particular, MMN was sensitive to the type of deviation (form or meaning) whereas the N400 was sensitive to the magnitude of the deviation rather than its type. WM capacity was associated with the ability to process phonological incoming information and semantic integration.
Highlights
The predictive brain hypothesis (Friston, 2009; Clark, 2013) describes the brain as an anticipatory organ that can generate predictions about the causal structure of the external world, based on the top-down influence of knowledge stored in longterm memory (Bar, 2007; Winkler et al, 2009; Friston, 2012)
Final words were presented in a background of white noise at a level of 50% intelligibility to induce adverse listening conditions loading on working memory (WM)
As a lower false alarm rate reflects better task performance, this result suggests that individuals with greater WM capacity were less likely to incorrectly classify final words phonologically related to the expected word as correct
Summary
The predictive brain hypothesis (Friston, 2009; Clark, 2013) describes the brain as an anticipatory organ that can generate predictions about the causal structure of the external world, based on the top-down influence of knowledge stored in longterm memory (Bar, 2007; Winkler et al, 2009; Friston, 2012). Numerous studies have shown that predictions about the form (i.e., phonology) and the meaning (i.e., semantics) of speech increase both its intelligibility (e.g., Miller et al, 1951; Davis and Johnsrude, 2007; Zekveld et al, 2011, 2013) and its perceptual clarity (Wild et al, 2012; Signoret et al, 2018; Signoret and Rudner, 2019) This facilitative effect could explain the enhanced perception of a speech event for which we already have knowledge stored in long-term memory – a phenomenon that leads to improved speech detection at a phonological level (see the "speech detection effect" in Signoret et al, 2011), better speech recognition at a lexical level (see the "word detection effect" in Signoret et al, 2011), and facilitated speech categorization at a semantic level (Daltrozzo et al, 2011; Rönnberg et al, 2019). Predictions about form and meaning have been shown to have an additive and independent facilitative effect on speech perception in that the meaning can still enhance the perceptual clarity of degraded speech even when total reliance on the form is possible (Signoret et al, 2018; Signoret and Rudner, 2019), suggesting that predictions about the form and the meaning could have different kinds of impact on neural speech processing
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