Since the appearance of machines, developed in order to aid humans in all kind of different tasks, one of the main issues has always been to provide a proper way of control on such machines, namely a user interface. Lately these interfaces have been rapidly evolving towards new ways of interaction. This book describes a new approach for the development of human-machine interfaces. In particular the case of pattern recognition systems based on Hidden Markov Models have been taken into account. The work starts from he development of techniques for the realization of natural language speech...