Partially-Shared Variational Auto-encoders for Unsupervised Domain Adaptation with Target Shift
This paper discusses unsupervised domain adaptation (UDA) with target shift, i.e., UDA with the non-identical label distributions of the source and target domains. In practice, this is an important problem; as we do not know labels in target domain datasets, we do not know whether or not its distribution is identical to that in the source domain dataset. Despite the inaccessibility to the shape of label distribution in the target domain, a common approach of modern UDA methods reduces the gap between the feature distributions of source and target domains, which implicitly assumes that the label distributions are identical, resulting in an unsatisfactory performance upon target shift. To overcome this problem, the proposed method, partially shared variational autoencoders (PS-VAEs), uses a pair-wise feature alignment instead of feature distribution matching. PS-VAEs inter-convert domain of each sample by a CycleGAN-based architecture while preserving its label-related content by sharing weights of two domain conversion branches as much as possible. To evaluate the performance of PS-VAEs, we carried out two experiments: UDA from synthesized data to real observation in human-pose estimation (regression) and UDA under controlled target shift intensities with digits datasets (classification). The proposed method outperformed the other methods in the regression task with a large margin while presenting its robustness with various levels of target shift."