For years, a number of speech scientists tried to reveal the mechanism of speech production based on observed acoustic signals and/or articulatory movements, and proposed a number of theories on the mechanism of speech production. However, most of them ignored the intermidate process which were important for the understanding of speech poduction - the motor commands and the activities of the central neural system. It is because both of them are difficult to be observed directly. This causes a gap between the linguistic representation and the corresponding physical observation in those theories. If we can uncover motor commands and activities of central neural systems in speech production, we may bridge the gap between linguistic representation and physical realization. This book focus on uncovering the motor commands and introduces a model-based approach to tackle this problem.