Learning From Positive and Unlabeled Data Using Observer-GAN

In the case of learning from positive and unlabeled data, the input data consist of (1) observations from the positive class and their corresponding labels and (2) unlabeled observations from both positive and negative classes. Generative Adversarial Networks (GANs) have been used to reduce the problem to the supervised setting with the advantage that supervised learning has state-of-the-art accuracy in classification tasks. In order to generate pseudo-negative observations, GANs are trained on positive and unlabeled observations with a modified loss. Using both positive and pseudo-negative observations leads to a supervised learning setting. The generation of pseudo-negative observations that are realistic enough to replace missing negative class samples is a bottleneck for current GAN-based algorithms. By including an additional classifier into the GAN architecture, we describe a novel GAN-based approach. The GAN discriminator instructs the generator to only produce samples that fall into the unlabeled data distribution, while a second classifier (observer) network monitors the GAN training to: (i) prevent the generated samples from falling into the positive distribution; and (ii) learn the features that are the key distinction between the positive and negative observations. Experiments on four image datasets demonstrate that our trained observer network performs better than existing techniques in discriminating between real unseen positive and negative samples.