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Abstract:
The aim of the dissertation presented here was to investigate neural correlates of the
processing of two different types of artificial grammar rules. The rules differed in
complexity. The Finite State Grammar (FSG) rule was specified by local adjacent
probabilities. In contrast, the Phrase Structure Grammar (PSG) rule generated hierarchical
dependencies via center-embeddings. Electrophysiological changes were recorded using
event-related brain potentials (ERPs) and hemodynamic changes were measured applying
functional Magnetic Resonance Imaging (fMRI). Within three experiments the structures
of the rules were systematically changed.
The processing of the two artificial grammar types revealed differences in the late
positivity on violations of the structures. The amplitude of the late positivity varied as a
function of the position of a violation of the sequence in the PSG rule. In contrast, no
changes of the amplitude of the varying violation positions of the FSG were found. FMRI
results revealed an increased activity in Broca’s area on violations of the PSG, but not of
the FSG. Additionally, the frontal operculum was associated with anomalies independent
of the rule type. Moreover, the direct contrast of PSG sequences versus FSG sequences
also correlated with an increased hemodynamic response function in Broca’s area and it’s
right hemispheric homologue.
The chunking of the elements of the artificial structure and the maintenance of the
particular element in working memory until the matching category occurred describes the
long distance dependencies of the PSG structure at hand. This process was correlated with
activity in Broca’s area in the present work. Hence, Broca’s area could be associated with
working memory demands during the processing of artificial hierarchical structures. These
finding could be interpreted as a potential key role of Broca’s area in a network of the
processing of hierarchical structures.
