  This paper explores the tasks of leveraging auxiliary modalities which are
only available at training to enhance multimodal representation learning
through cross-modal Knowledge Distillation (KD). The widely adopted mutual
information maximization-based objective leads to a short-cut solution of the
weak teacher, i.e., achieving the maximum mutual information by simply making
the teacher model as weak as the student model. To prevent such a weak
solution, we introduce an additional objective term, i.e., the mutual
information between the teacher and the auxiliary modality model. Besides, to
narrow down the information gap between the student and teacher, we further
propose to minimize the conditional entropy of the teacher given the student.
Novel training schemes based on contrastive learning and adversarial learning
are designed to optimize the mutual information and the conditional entropy,
respectively. Experimental results on three popular multimodal benchmark
datasets have shown that the proposed method outperforms a range of
state-of-the-art approaches for video recognition, video retrieval and emotion
classification.
