Imaginative Perception Tokens Enhance Spatial Reasoning in Multimodal Language ModelsMahtab Bigverdi, Linjie Li, Weikai Huang, Jieyu Zhang, Tuhin Kundu, Zelun Luo, Chris Kim, Jaemin Cho, Ranjay Krishna, Linda Shapiro, Liu Yiming
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Vision-language models (VLMs) excel at many tasks, yetcontinue to struggle with spatial reasoning, problems where the key in-formation is not directly observable in the input. Many spatial questionsrequire imaginative perception: simulating an unseen viewpoint, tracinga trajectory through an occluded space, or integrating partial views intoa coherent spatial map. Humans naturally support this kind of reason-ing through imagination. Prior work has introduced intermediate visualrepresentations (e.g., visual thoughts, depth, or box tokens), but theseintermediates often refine structure already visible rather than predict-ing the missing spatial structure implied by the evidence. We introduceImaginative Perception Tokens (IPT), intermediate perceptual rep-resentations that externalize what a VLM would perceive under an alter-native spatial configuration while remaining consistent with the observedinput. To study this capability, we formulate three tasks that requireimaginative perception: Perspective Taking (PET), Path Tracing(PT), and Multiview Counting (MVC). For each task, we constructdatasets of →20K examples spanning simulated and real-world settings,paired with ground-truth intermediate imaginations, final answers, andcurated evaluation benchmarks. Using the unified VLM BAGEL [12] asour backbone, IPT supervision improves spatial reasoning across severalsettings and often outperforms textual chain-of-thought training, evenwhen no image is generated at inference time. For example, on MVC,IPT improves accuracy by 3.4% and achieves performance competitivewith strong closed-source models on Path Tracing. We also find thatmixed training with IPT and label-only data can further improve perfor-mance. In contrast, textual chain-of-thought can be detrimental on thesetasks, substantially degrading performance in some cases, highlighting amodality mismatch when forcing spatial computation through language.Overall, IPT provides a principled supervision signal for reasoning overunobserved structure, yielding stronger spatial generalization and a moreinterpretable intermediate aligned with the underlying geometry of thetask. Code will be released at the project page.Path Tracing (11k)Question: As you move from waypoint 1 to 2. This is what you see looking forward from Question: Which object can you seepoint 1: <image_2>. This is what you see looking forward from point 2: <image_3>. on your right side at waypoint M?Which object can you see on your left side at waypoint M?Options: Imagination1 M 2A. A dining table 2 22B. A fridge MC. A countertop 1D. A sofa 1 13Perspective Taking (55k)Question: After moving to the marked ‘X’ position on the ground while keeping my Question: Will the sideboard appearcurrent orientation, then turning left for 90 degrees, will the sideboard appear closer closer or further away?or further away?Options:A. CloserB. Further XX1 ImaginationMultiview Counting (17k)Question: What is the total number of office chairs in this scene? Question: How many refrigerator(s)are in this area?Answers: 8 Imagination1 23 4Fig. 1: Overview of the three spatial imagination tasks. The left columns showtraining examples with ground-truth imaginative perception; the right columns showevaluation examples.