Motion illusions arise from light source ambiguity
Motion illusions such as the rotating snakes illusion or the rotating cube illusion remain unexplained. Recently, Watanabe et al. showed that this category of illusions might be related to predictive coding.
Unlike existing research focusing on 2D patterns, we propose that all motion illusions arise from predictions of the visual system resolving 3D light-and-shadow patterns perceived as ambiguous. All motion illusions can be understood as mimicking the shadow pattern caused by the relative motion of a light source and an object.
For example, the rotating snakes illusion in Fig. 4c can be understood as a 3D black and white wavy object seen from above,with grey shadows projected by a light source moving clockwise as to stay perpendicular to each wave crest (attachment: same illusion recreated with a real object).
Without the light source being explicitly visible,the pattern could be caused by (1) The light moving relatively to a static object or (2) the object moving in the opposite direction relatively to a static light source.
Without cues, in a statically lit environment, the visual system resolves the ambiguity by assuming the most likely scenario: the object must be moving, the light is not.
Attachment: shadows.pdf (516 KB)