Linguistic Bias Modulates Interpretation of Speech via Neural Delta-Band Oscillations

TLDR

Language comprehension groups words into syntactic phrases, and although acoustic and syntactic grouping usually align, ambiguous sentences can lead to groupings that contradict prosody. The study hypothesized that linguistic grouping bias modulates the interpretational impact of speech prosody in ambiguous situations, detectable through delta‑band oscillations. Delta‑band oscillatory phase at the critical word should reflect whether participants terminate a phrase despite the absence of acoustic boundary cues. In an EEG study, interpretation of ambiguous sentences depended on prosodic boundaries, with delta‑band phase at the critical word reflecting phrase termination, and participants’ internal grouping bias modulated prosody independently of acoustic cues.

Abstract

Language comprehension requires that single words be grouped into syntactic phrases, as words in sentences are too many to memorize individually. In speech, acoustic and syntactic grouping patterns mostly align. However, when ambiguous sentences allow for alternative grouping patterns, comprehenders may form phrases that contradict speech prosody. While delta-band oscillations are known to track prosody, we hypothesized that linguistic grouping bias can modulate the interpretational impact of speech prosody in ambiguous situations, which should surface in delta-band oscillations when grouping patterns chosen by comprehenders differ from those indicated by prosody. In our auditory electroencephalography study, the interpretation of ambiguous sentences depended on whether an identical word was either followed by a prosodic boundary or not, thereby signaling the ending or continuation of the current phrase. Delta-band oscillatory phase at the critical word should reflect whether participants terminate a phrase despite a lack of acoustic boundary cues. Crossing speech prosody with participants' grouping choice, we observed a main effect of grouping choice—independent of prosody. An internal linguistic bias for grouping words into phrases can thus modulate the interpretational impact of speech prosody via delta-band oscillatory phase.