Motion-from-Structure in Face Perception: Expectations of Natural Face Motion Depend on Face Shape

Anatomical features that define facial identity also influence how a face moves during expres- sion. This overlap suggests the visual system might form expectations about facial motion based on shape. However, recent theories propose that facial shape and motion are processed in independent brain pathways. We used reverse correlation to test whether expectations about natural facial movement are shaped by facial structure, and vice versa. Participants judged syn- thetic dynamic faces with randomly varying shape or motion. We estimated expected speed of facial expression components and compared these across different identities. We also identified shape features used for face recognition and assessed whether these changed with familiar ver- sus unfamiliar motion. Our results show that expectations of natural motion during expression are influenced by face shape, but the shape features used for identification remain stable across motion contexts. We interpret these findings within the independent pathways framework, suggesting a form of motion-from-structure processing.