In this section, we will briefly review several works which involve or are closely related to the task of lipreading. The works described below have been grouped into five general categories which roughly correspond to their respective primary processing techniques. The details of many of these processing techniques may be found in Section 3. It is important to note that the works cited below are all technically-oriented in nature, and that there exists an even larger body of work in the literature which address the psychophysical aspects of lipreading. For a review of these works, see [Sum92], [DC87].