Leveraging Knowledge of Modality Experts for Incomplete Multimodal Learning

Multimodal Emotion Recognition (MER) may encounter incomplete multimodal scenarios caused by sensor damage or privacy protection in practical applications. Existing incomplete multimodal learning methods focus on learning better joint representations across modalities. However, our investigation shows that they are lacking in learning the unimodal representations which are rather discriminative as well. Instead, we propose a novel framework named Mixture of Modality Knowledge Experts (MoMKE) with two-stage training. In unimodal expert training, each expert learns the unimodal knowledge from the corresponding modality. In experts mixing training, both unimodal and joint representations are learned by leveraging the knowledge of all modality experts. In addition, we design a special Soft Router that can enrich the modality representations by dynamically mixing the unimodal representations and the joint representations. Various incomplete multimodal experiments on three benchmark datasets showcase the robust performance of MoMKE, especially on severely incomplete conditions. Visualization analysis further reveals the considerable value of unimodal and joint representations. Codes are realised at https://github.com/wxxv/MoMKE.