Periodic Reporting for period 1 - RhythmicPrediction (Rhythmic prediction in speech perception: are our brain waves in sync with our native language?)
Reporting period: 2021-01-01 to 2022-12-31
Speech has rhythmic properties that widely differ across languages. When we listen to foreign languages, we may perceive them to be more musical, or rather more rap-like than our own. Even if we are unaware of it, the rhythm and melody of language, i.e. prosody, reflects its linguistic structure. On the one hand, prosody emphasizes content words and new information with stress and accents. On the other hand, it is aligned to phrase edges, marking them with boundary tones. Prosody hence helps the listener to focus on important words and to chunk sentences into phrases, and phrases into words. In fact, prosody is even used predictively, for instance to time the onset of the next word, the next piece of new information, or the total remaining length of the utterance, so the listener can seamlessly start their own speaking turn. So, the listener, or rather their brain, is actively predicting when important speech events will happen, using prosody. How prosodic rhythms are exploited to predict speech timing, however, is unclear. No link between prosody and neural predictive processing has yet been empirically made. One hypothesis is that rhythm, such as the alternation of stressed and unstressed syllables, helps listeners time their attention. Similar behavior is best captured by the notion of an internal oscillator which can be set straight by attentional spikes. While neuroscientific evidence for the relation of neural oscillators to speech processing is starting to emerge, no link to the use of prosody nor predictive listening exists, yet. Furthermore, it is still unknown how native language knowledge affects cortical oscillations, and how oscillations are affected by cross-linguistic differences in rhythmic structure. The current project combines the standing knowledge of prosodic typology with the recent advances in neuroscience on cortical oscillations, to investigate the role of internal oscillators on native prosody perception, and active speech prediction.
Through the collection of data on spontaneous speech rhythms in Swiss German, French and Italian, the project empirically tested the Macro Rhythm Hypothesis which postulates in what ways languages differ in their slow prosodic rhythms. The project furthermore tested the difference between temporal variability and structural periodicity and found more cross-linguistic differences in the latter than in the former. The findings in the spontaneous speech data were in turn connected to the perception of this same speech through the collection of neural data of participants listening to their own language as well as to the other two languages. The results are projected to give insights into predictive timing mechanisms in the brain through the analysis of the synchronization of top-down slow cortical oscillations with slow structural rhythms in native speech, versus the known synchronization of faster bottom-up cortical responses to patterns specific to the perceived stimulus. Furthermore, native speech perception is hypothesized to be more strongly related to structural periodicity, i.e. more abstract pattern repetitions, while non-native speech perception is hypothesized to be more strongly related to temporal variability.
The project surpasses the state of the art in speech perception research in neuroscience in ecological validity and cross-linguistic typology. Within cortical oscillatory research it is one of few to study the perception of non-performative spontaneous speech and it is innovative in its direct comparative linguistic research of prosodic perceptual chunking. Its findings contribute to our understanding of the mechanisms behind the processing of natural speech and the role of rhythm across languages.