  In this report, we describe the technical details of our submission to the
2021 EPIC-KITCHENS-100 Unsupervised Domain Adaptation Challenge for Action
Recognition. Leveraging multiple modalities has been proved to benefit the
Unsupervised Domain Adaptation (UDA) task. In this work, we present Multi-Modal
Mutual Enhancement Module (M3EM), a deep module for jointly considering
information from multiple modalities to find the most transferable
representations across domains. We achieve this by implementing two sub-modules
for enhancing each modality using the context of other modalities. The first
sub-module exchanges information across modalities through the semantic space,
while the second sub-module finds the most transferable spatial region based on
the consensus of all modalities.
