For the mouth, teeth were made to give a bit more realism when the mouth was opened. Conformation parameters simulate the differences between faces, for example, nose shape, rather than the change in expression on a single face. Once the model is set up, the next step is to work out how the parameters should vary over time. The theory behind this is taken from traditional animtion techniques. From them, it is possible to find out what movements are involved in each facial expression.
Medical books are also a good source of information about facial movements.
Speech synchronisation involves matching the movements of the mouth with a recorded speech track. Many levels of animation were attempted. Parke concludes that the most useful parameters are the ones involved in mouth, eye and jaw movement. He states the symmetry of the model, although easing the complexity of the model, is a deficiency as it cuts out a lot of expressions and reduces the realism of the image. He refers to the parameterised system as an instrument we do not yet know how to play.