SpatialLadder: Progressive Training for Spatial Reasoning in Vision-Language Models - Li, Hongxing; Li, Dingming; Wang, Zixuan; Yan, Yuchen; Wu, Hang; Zhang, Wenqi; Shen, Yongliang; Lu, Weiming; Xiao, Jun; Zhuang, Yueting (International Conference on Learning Representations, 2026)