Cortical tracking of complex spoken sentences
Humans naturally tune in to the rhythm of speech (Giraud & Poeppel, 2012). Recent work has shown that low-frequency brain rhythms have been shown concurrently to track the main constituents in a linguistic hierarchy: phrases and sentences (Ding et al., 2016). Notably, brain rhythms were cross-linguistically tested using isochronous speech in English and Mandarin Chinese. Given the variable nature of linguistic constituents, it is however unclear whether the implicit knowledge of linguistic structure contributes in tracking linguistic constituents (phrases, sentences) of variable duration. We tested whether neural rhythms are sensitive to changes in constituent size, extending Ding et al.'s paradigm to German. We used electroencephalography to record the neural response to 4-word and 5-word sentences. Results show that the brain entrains to the purely top-down rhythm of sentences independently from the stimulation rhythm. Sentence rhythms generate a harmonic structure of their own, a direct marker of perceived language hierarchy.