A Boosting Approach to Multiview Classification with Cooperation

In many fields, such as bioinformatics or multimedia, data may be described using different sets of features (or views) which carry either global or local information. Some learning tasks make use of these several views in order to improve overall predictive power of classifiers through fusion-based methods. Usually, these approaches rely on a weighted combination of classifiers (or selected descriptions), where classifiers are learned independently. One drawback of these methods is that the classifier learned on one view does not communicate its failures within the other views. This paper deals with a novel approach to integrate multiview information. The proposed algorithm, named Mumbo, is based on boosting. Within the boosting scheme, Mumbo maintains one distribution of examples on each view, and at each round, it learns one weak classifier on each view. Within a view, the distribution of examples evolves both with the ability of the dedicated classifier to deal with examples of the corresponding features space, and with the ability of classifiers in other views to process the same examples within their own description spaces. Hence, the principle is to slightly remove the hard examples from the learning space of one view, while their weights get higher in the other views. This way, we expect that examples are urged to be processed by the most appropriate views, when possible. At the end of the iterative learning process, a final classifier is computed by a weighted combination of selected weak classifiers. This paper provides the Mumbo algorithm in a multiclass and multiview setting, based on recent theoretical advances in boosting. The boosting properties of Mumbo are proved, as well as some results on its generalization capabilities. Several experimental results are reported which point out that complementary views may actually cooperate under some assumptions.