  Contrastive learning models based on Siamese structure have demonstrated
remarkable performance in self-supervised learning. Such a success of
contrastive learning relies on two conditions, a sufficient number of positive
pairs and adequate variations between them. If the conditions are not met,
these frameworks will lack semantic contrast and be fragile on overfitting. To
address these two issues, we propose Hallucinator that could efficiently
generate additional positive samples for further contrast. The Hallucinator is
differentiable and creates new data in the feature space. Thus, it is optimized
directly with the pre-training task and introduces nearly negligible
computation. Moreover, we reduce the mutual information of hallucinated pairs
and smooth them through non-linear operations. This process helps avoid
over-confident contrastive learning models during the training and achieves
more transformation-invariant feature embeddings. Remarkably, we empirically
prove that the proposed Hallucinator generalizes well to various contrastive
learning models, including MoCoV1&V2, SimCLR and SimSiam. Under the linear
classification protocol, a stable accuracy gain is achieved, ranging from 0.3%
to 3.0% on CIFAR10&100, Tiny ImageNet, STL-10 and ImageNet. The improvement is
also observed in transferring pre-train encoders to the downstream tasks,
including object detection and segmentation.
