Learning by Actively Querying Strong Modal Features

Complex objects are usually with multiple modal features. In multi-modal learning, modalities closely related to the target tasks are known as strong modalities. While collecting strong modalities of all instances is often expensive, and current multi-modal learning techniques hardly take the strong modal feature extraction expenses into consideration. On the other hand, active learning is proposed to reduce the labeling expenses by querying the ground truths for specific selected instances. In this paper, we propose a training strategy, ACQUEST (ACtive QUErying STrong modalities), which exploits strong modal information by actively querying the strong modal feature values of “selected” instances rather than their corresponding ground truths. In ACQUEST, only the informative instances are selected for strong modal feature acquisition. An inverse prediction technique is also proposed to make the ACQUEST a unified optimization form. Experiments on image datasets show that ACQUEST achieves better classification performance than conventional active learning and multi-modal learning methods with less feature acquisition costs and labeling expenses.