de Diego-Balaguer, R. 1, 2, 3, 4 , Lopez-Barroso, D. 2 , Rodriguez-Fornells, A. 1, 2 & Bachoud-Lévi, A. 3, 4, 5, 6
1 ICREA
2 University of Barcelona and IDIBELL, Barcelona, Spain
3 UPEC and IRBM, Créteil, France
4 Ecole Normale Supérieure, Paris, France
5 AP-HP Groupe Henri-Mondor Albert-Chenevier, Créteil, France
6 Centre de référence Maladie de Huntington, Créteil, France
Prosody is a rhythmic cue that has a critical role in speech processing. However, the mechanism by which prosodic information affects the way we treat the speech signal and influences learning is scarcely understood. In two different experiments we recorded event-related potentials (ERPs) and functional hemodynamic changes (fMRI) while participants were learning artificial languages with and without prosodic cues, implemented by the introduction of subtle pauses between words. Languages were built concatenating trisyllabic words with embedded rules (e.g.“puliku, pufaku, pureku”) analogous to simple morphosyntactic dependencies (e.g.“is playing, is dancing, is talking”). The absence of prosodic cues induced a selective increase of activation in the left ventrolateral prefrontal cortex both for structured language and for random syllable streams where learning was not possible. In the ERP experiment, this effect arose very early in sensory processing in a negative increase around 100 ms after syllable onset (N1 component). Structured streams with prosodic cues showed an additional positive going increase around 200 ms (P2 component) associated to rule learning. This effect characterised also those participants that learned the rule in the absence of prosodic information displaying increased bilateral medial parietal cortex activation associated to the top-down attention system. Two conclusions could be derived from the present pattern of results: (i) prosody helps segmentation acting as a sensory cue that automatically triggers attention and (ii) it helps as a cue to reorient attention to timing information relevant for rule learning. This function fits well with the observation that in natural languages prosodic boundaries in speech coincide with syntactic boundaries.