Cross-modal Semantic Alignment Pre-training for Vision-and-Language Navigation

Vision-and-Language Navigation needs an agent to navigate to a target location by progressively grounding and following the relevant instruction conditioning on its memory and current observation. Existing works utilize the cross-modal transformer to pass the message between visual modality and textual modality. However, they are still limited to mining the fine-grained matching between the underlying components of trajectories and instructions. Inspired by the significant progress achieved by large-scale pre-training methods, in this paper, we propose CSAP, a new method of Cross-modal Semantic Alignment Pre-training for Vision-and-Language Navigation. It is designed to learn the alignment from trajectory-instruction pairs through two novel tasks, including trajectory-conditioned masked fragment modeling and contrastive semantic-alignment modeling. Specifically, the trajectory-conditioned masked fragment modeling encourages the agent to extract useful visual information to reconstruct the masked fragment. The contrastive semantic-alignment modeling is designed to align the visual representation with corresponding phrase embeddings. By showing experimental results on the benchmark dataset, we demonstrate that transformer architecture-based navigation agent pre-trained with our proposed CSAP outperforms existing methods on both SR and SPL scores.