Wednesday November 22nd 2017, 3:00pm
During speech comprehension continuous speech needs to be segmented to yield chunks that correspond to linguistic units for further processing. The phase-locking of cortical theta oscillations to the speech acoustics provides a mechanism for this temporal segmentation. Linguistic processing may affect the temporal segmentation of the speech acoustics possibly due to a top-down modulation. Specific temporal dynamics might underlie this hierarchical processing, involving connectivity between frontal, motor areas and auditory cortex in the delta- and theta-band. It is unclear, however, at which linguistic level top-down effects occur and which mechanisms underlie this interaction. Here, we probe the temporal dynamics of hierarchical language processing.
We recorded Magnetoencephalography during a frequency-tagging paradigm to investigate effects of lexical access and sub-lexical contingencies on the temporal segmentation at the syllabic scale. Two experiments were conducted: Experiment 1, with sequences of German (native) and Turkish (foreign) words, and Experiment 2, with sequences of German and Non-Turkish words (without sub-lexical contingencies). Syllable rate was 4 syllables/sec and word rate was 2 words/sec. Acoustic cues and sub-lexical contingencies for word grouping were removed and controlled between languages. In Experiment 1, we hypothesized brain-wave spectral peaks at 2 Hz due to lexical access, for German stimuli but not for Turkish stimuli. In Experiment 2, the effect of sub-lexical statistics was measured. In both experiments we expected top-down effects to increase connectivity between higher order processing areas and the auditory cortex.
Our findings provide evidence for lexical segmentation at 2 Hz in frontal and temporal brain areas. Interestingly, participants were sensitive to sub-lexical contingencies even when listening to a non-native language. Sub-lexical contingencies resulted in broad activation increases in frontal, temporal and motor areas at 2 Hz. The findings provide new insights into the temporal dynamics and localization of hierarchical lexical-related processes.
Dr Johanna Rimmele
Post-Doctoral Fellow
from the Max Planck Institute for Empirical Aesthetics
Dr Anne Keitel