Overt and implicit prosody contribute to neurophysiological responses previously attributed to grammatical processing

Abstract

Recent neurophysiological research suggests that slow cortical activity tracks hierarchical syntactic structure during online sentence processing. Here we tested an alternative hypothesis: electrophysiological activity peaks at constituent phrase as well as sentence frequencies reflect cortical tracking of overt or covert (implicit) prosodic grouping. Participants listened to series of sentences presented in three conditions while electroencephalography (EEG) was recorded. First, prosodic cues in the sentence materials were neutralized. We found an EEG spectral power peak elicited at a frequency that only ‘tagged’ covert, implicit prosodic change, but not any major syntactic constituents. In the second condition, participants listened to a series of sentences with overt prosodic grouping cues that either aligned or misaligned with the syntactic phrasing in the sentences (initial overt prosody trials). Following each overt prosody trial, participants were presented with a second series of sentences lacking overt prosodic cues (instructed prosody trial) and were instructed to imagine the prosodic contour present in the previous, overt prosody trial. The EEG responses reflected an interactive relationship between syntactic processing and prosodic tracking at the frequencies of syntactic constituents (sentences and phrases): alignment of syntax and prosody boosted EEG responses, whereas their misalignment had an opposite effect. This was true for both overt and imagined prosody conditions. We conclude that processing of both overt and covert prosody is reflected in the frequency-tagged neural responses at sentence constituent frequencies. These findings need to be incorporated in any account that aims to identify neural markers reflecting syntactic processing.

Neural synchrony reflects closure of jabberwocky noun phrases but not predictable pseudoword sequences

“…While we suggest above that the increased phrase band ITPC may index the formation of type‐based syntactic constituents, others have shown that such responses may also be generated by neural processes related to prosody (Boucher et al, 2019; Glushko et al, 2022). For example, Boucher et al reported that auditorily presented French clauses and pseudoword sequences elicited comparable delta ITPC when matched for prosody, while less ITPC was elicited by prosodically matched nonspeech tones.…”

“…Because their pseudoword sequences did not obviously correspond to syntactic structures, the authors suggested that low‐frequency ITPC likely arises from processing acoustic chunks corresponding to speech‐specific prosodic boundaries, rather than syntactic processes. There is also evidence that phase synchrony may arise from implicitly generated prosodic boundaries, even when these markers do not necessarily correspond with the closure of syntactic constituents (Glushko et al, 2022). Accordingly, we cannot entirely reject the possibility that the increased phrase band ITPC reported here was driven (at least in part) by prosodic information.…”

“…Recent studies have sought to further probe this effect. However, even those employing highly similar paradigms have yielded variable results, suggesting that the effect may be sensitive to additional cognitive‐linguistic factors such as covert prosody (e.g., Boucher et al, 2019; Glushko et al, 2022), lexical‐semantic relatedness (Frank & Yang, 2018), and semantic composition (Kaufeld et al, 2020).…”

Speech prosody enhances the neural processing of syntax

“…It is thus possible to hypothesize that the regular interaction between and co-occurrence of these two linguistic features has driven the brain into expecting syntactic and prosodic representations to be coherent even if one of the two is not explicitly present, or when they do not co-occur. In line with this, a recent study has demonstrated that the cortical tracking of naturalistic speech is enhanced when overt and covert prosodic boundaries are aligned with the syntactic structure compared to when they are misaligned 34 .…”

Intonation Units in spontaneous speech evoke a neural response

“…Second, listeners perceive prosodic breaks at syntactic boundaries even when no acoustic cue for such a break exists (Buxó-Lugo & Watson, 2016; Cole et al, 2010). Thus, it is possible that delta-band neural speech tracking reflects some type of prosodic processing nonetheless (Gilbert et al, 2015; Glushko et al, 2022; Henke & Meyer, 2021).…”