Emotion Recognition from Speech: An Unsupervised Learning Approach

Speech processing is quickly shifting toward affective computing, that requires handling emotions and modeling expressive speech synthesis and recognition. The latter task has been so far achieved by supervised classifiers. This implies a prior labeling and data preprocessing, with a cost that increases with the size of the database, in addition to the risk of committing errors. A typical emotion recognition corpus therefore has a relatively limited number of instances. To avoid the cost of labeling, and at the same time to reduce the risk of overfitting due to lack of data, unsupervised learning seems a suitable alternative to recognize emotions from speech. The recent advances in clustering techniques make it possible to reach good performances, comparable to that obtained by classifiers, with much less preprocessing load and even with generalization guarantees. This paper presents a novel approach for emotion recognition from speech signal, based on some variants of fuzzy clustering, such as probabilistic, possibilistic and graded-possibilistic fuzzy c-means. Experiments indicate that this approach (a) is effective in recognition, with in-corpus performances comparable to other proposals in the literature but with the added value of complexity control and (b) allows an innovative way to analyze emotions conveyed by speech using possibilistic membership degrees.