Marian Bartlett, Gianluca Donato, Javier Movellan, Joseph Hager, Paul Ekman, Terrence J. Sejnowski
The Facial Action Coding System (FACS) (9) is an objective method for quantifying facial movement in terms of component actions. This system is widely used in behavioral investigations of emotion, cognitive processes, and social interaction. The cod(cid:173) ing is presently performed by highly trained human experts. This paper explores and compares techniques for automatically recog(cid:173) nizing facial actions in sequences of images. These methods include unsupervised learning techniques for finding basis images such as principal component analysis, independent component analysis and local feature analysis, and supervised learning techniques such as Fisher's linear discriminants. These data-driven bases are com(cid:173) pared to Gabor wavelets, in which the basis images are predefined. Best performances were obtained using the Gabor wavelet repre(cid:173) sentation and the independent component representation, both of which achieved 96% accuracy for classifying 12 facial actions. The ICA representation employs 2 orders of magnitude fewer basis im(cid:173) ages than the Gabor representation and takes 90% less CPU time to compute for new images. The results provide converging support for using local basis images, high spatial frequencies, and statistical independence for classifying facial actions.