Representations of geometric shapes have syntactic structure

Recent research suggests that humans use language-like mental representations for many classes of stimuli, from auditory sequences to visual shapes. However, evidence has been largely indirect, relying on stimulus complexity and compression as a proxy for internal representation. In this study, we probe the structure of geometric shape representations more directly. Instead of complexity measures, we rely on constituency tests similar to those used in linguistics and probe whether geometric shapes exhibit structural ambiguity, constituent subparts, and syntactic movement. Across three preregistered experiments (n = 136) using a rigorously controlled set of stimuli, we find robust evidence for tree structure in human adults' shape representations. First, the same shape can receive different structural representations depending on how a preceding animation organizes it. Second, subparts of shapes are easier to detect when they belong to the same subtree than when they span different subtrees. Third, shape fragments are easier to reconfigure the higher in the tree they are split. These results support the hypothesis that a geometric shape is internally represented as a hierarchical tree of constituents nested inside each other. Thus, while geometric shapes differ in many ways from natural-language sentences, they are nevertheless encoded by humans in a language-like representational format. (PsycInfo Database Record (c) 2026 APA, all rights reserved).