A linear model of acoustic-to-facial mapping: model parameters, data set size, and generalization across speakers.

The relationship between acoustic and visual speech is important for understanding speech perception, but it also forms the basis behind a type of facial animator, which can predict facial motion during speech given an acoustic input. This relationship was examined by revisiting a linear transformation model of audio-visual speech production. A mathematical model is constructed whereby the visual aspect of speech is reproduced from the acoustic signal via a linear transformation. Unlike previous studies in this area, this paper will address specific aspects of the model as related to the effects of window size for acoustic framing and the critical size of the training set. On average, facial motion is predicted with a correlation of 0.70 to the recorded motion, when the model is trained and then tested on the same subject. This is comparable to previous studies using either similar or different model approaches. Using a model trained on other subjects and then applying it to a new subject resulted in a prediction correlation of 0.65. Furthermore, acoustic windows of 100 ms and a data set of approximately 40 sentences are required for maximum predictability. The results are interpreted in terms of the underlying assumptions of the model.