Investigations into the neural representation of prosodic, lexical, and syntactic properties of spontaneous, natural speech production using electrocorticography (ECoG)

The present thesis reports on interdisciplinary attempts to elucidate the hitherto unexplored neural correlates of linguistic processing in conditions of non-experimental, natural overt speech production. To this end, the author of this thesis, supported by colleagues, built up a multimodal neurolinguistic corpus (“The Freiburg/First Neurolinguistic Corpus”), composed of synchronized audio, video, electrocorticographic (ECoG) materials and linguistic annotations on different levels of linguistic abstraction. This corpus allowed us to study the neural effects related to several aspects of natural language, each of whom was treated in a separate study. Study 1 was dedicated to prosody and addressed the neural activity related to the production of the focus accent, Study 2 was dedicated to questions related to the neural representation of word complexity, and Study 3 investigated the syntactic processing accompanying natural clause production. The psycholinguistic methods we used consisted of (i) application of a matching procedure to select controlled word categories out of the natural language data (Study 1), (ii) orthogonalization of the linguistic parameters with the help of a linear regression model to overcome the problem of collinearity between correlated linguistic parameters, and (iii) the usage of a principal component analysis to extract most informative components of the linguistic material. The neuroscientific approach consisted either of group comparisons, in which neural effects underlying linguistically distinctive groups of words were compared (Study 1) or of correlation of neural activity with individual linguistic parameters (Study 2) and with principal components explaining most of the variances in the linguistic data (Study 3). We were interested in neural effects reflecting differences in the effort related to the production of speech units of different linguistic complexity. We were looking for neural effects which would be spatially focalized and which would be manifested in gamma activity ...