Invariant Coding of Local Biological Motion Signals: Evidence for a ‘Life Motion Detector’ in the Human Brain

Humans are remarkably adept at detecting the movement of biological entities, even from local biological motion (BM) signals without any global configuration. However, it remains unclear whether the brain encodes the invariant local biological kinematics. In this study, we utilized an adaptation paradigm and demonstrated that after adapting to a side view of local BM, the perceived moving direction of an intact human walker near the frontal view was significantly biased in the opposite direction, resulting in a perceptual aftereffect. Notably, this adaptation aftereffect persisted across different species (pigeon, cat, dog) and various actions (running, crawling, cycling). However, the effect disappeared when the adaptors were inverted, critical kinematic information was removed, or the test BM stimulus was replaced with object motion. These findings provide compelling evidence for the invariant coding of local BM signals tuned to specific moving direction, supporting the existence of “life motion detector” in the human brain.