How to break the configuration of moving objects? Geometric invariance in visual working memory

Visual working memory is highly sensitive to global configurations in addition to the features of each object. When objects move, their configuration varies correspondingly. In this study, we explored the geometric rules governing the maintenance of a dynamic configuration in visual working memory. Our investigation is guided by Klein's Erlangen program, a hierarchy of geometric stability that includes affine, projective, and topological invariants. In a change-detection task, memory displays were categorized by which geometric invariance was violated by the objects' motions. The results showed that (a) there was no decrement in memory performance until the projective invariance was violated, (b) more dramatic changes (such as a topological change) did not further enlarge the decrement, and (c) objects causing the violation of projective invariance were better encoded into memory. These results collectively demonstrate that projective invariance is the only geometric property determining the maintenance of a dynamic configuration in visual working memory.