Towards a Causally-inspired Evolving World Model for Vision-and-Language Navigation in Continuous Environments

Vision-and-Language Navigation in Continuous Environments (VLN-CE) has emerged as a pivotal challenge in Embodied AI, requiring an agent to navigate 3D spaces guided by natural language instructions. Drawing inspiration from human cognition, world models provide a powerful paradigm by predicting environment dynamics and enabling reasoning beyond immediate observations. However, existing world model-based VLN methods remain static once trained - their representations rely on fixed correlationbased priors rather than adaptive causal structures, making them unable to accommodate evolving confounders and changing observation-action dependencies across environments. This rigidity leads to overfitting to training-specific patterns and degraded performance under distribution shifts. To address this limitation, we propose a causally-inspired evolving world modeling framework that formulates VLN-CE as a sequence of causal partially observable Markov decision processes. Our model learns unified latent states that integrate vision, language, and action, while addressing spurious correlations through a dual-level intervention mechanism: at the observation level, frequency-domain perturbations simulate superficial appearance variations to enhance perceptual robustness; at the representation level, cross-episode confounder buffers perform counterfactual substitution to approximate the influence of latent confounding factors. Beyond static world modeling, our framework continuously evolves, refining these proxy representations across episodes, enabling efficient adaptation to previously unseen environments. Building on this evolving causally-inspired foundation, our world model supports counterfactual reasoning and strengthens generalization across diverse navigation contexts. Extensive evaluations on established VLN-CE benchmarks demonstrate that our method outperforms existing approaches, delivering superior navigation performance across diverse scenarios. Real-world robot evaluations further validate the practicality of our approach. Code is available in the Supplementary Material.