The Johansson-Muybridge Effect: A Forensic Framework for Distinguishing Authentic from Synthetic Video — v4.5

The framework derives its name from two foundational figures in motion perception: Gunnar Johansson, whose biological motion experiments demonstrated that humans extract velocity and direction from minimal visual cues, and Eadweard Muybridge, whose sequential frame photography established that temporal continuity encodes true physics. The core diagnostic instrument is the spacetime slice — a pixel-row stack across sequential frames that renders velocity as diagonal streaks. Authentic motion produces coherent, physically-grounded trajectories; synthetic interpolation produces characteristic smearing artifacts that nonetheless carry extractable velocity and direction information. v4.5 introduces a key theoretical advance: AI-generated video does not merely fail to simulate continuous motion — it structurally simulates a cross-fade at every frame interval. Lacking true temporal physics, generative models interpolate pixel states between keyframes, producing the perceptual equivalent of a continuous dissolve. This cross-fade signature is not an edge case but an architectural inevitability, and it is legible in spacetime analysis. The framework has been validated through cross-substrate testing across multiple AI inference engines. Implementation is provided as ANA (Authentic/Native Analyzer), a forensic pipeline producing spacetime slices, motion heatmaps, temporal curves, and AUTHENTIC/SYNTHETIC LEAN verdicts with confidence scores.