i Ich erkläre hiermit, dass ich die vorliegende Arbeit selbstständig verfasst und keine anderen als die angegebenen Quellen und Hilfsmittel verwendet habe. Karlsruhe, den 31.7.2006 Marek Wester ii iii Abstract Communication in quiet settings or for locked-in patients is not easy without disturbing others or even impossible. A device enabling to communicate without the production of sound or controlled muscle movements would be the solution and the goal of this research. A feasibility study on

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... e possibility of the recognition of speech in five different modalities based on EEG brain waves was done in this work. This modalities were: normal speech, whispered speech, silent speech, mumbled speech and unspoken speech. Unspoken speech in our understanding is speech that is uttered just in the mind without any muscle movement. The focus of this recognition task was on the recognition of unspoken speech. Furthermore we wanted to investigate which regions of the brain are most important for the recognition of unspoken speech. The results of the experiments conducted for this work show that speech recognition based on EEG brain waves is possible with a word accuracy which is in average 4 to 5 times higher than chance with vocabularies of up to ten words for most of the recorded sessions. The regions which are important for unspoken speech recognition were identified as the homunculus, the Broca's area and the Wernicke's area.