Oriented structure of the occlusion distortion: is it reliable?

In the energy spectrum of an occlusion sequence, the distortion term has the same orientation as the velocity of the occluding signal. Other works claimed that this oriented structure can be used to distinguish the occluding velocity from the occluded one. We argue that the orientation structure of the distortion cannot always work as a reliable feature due to the rapidly decreasing energy contribution. This already weak orientation structure is further blurred by a superposition of distinct distortion components. We also indicate that the superposition principle of Shizawa and Mase (1991) for multiple motion estimation needs to be adjusted.