Manifest Illusions

The notion of illusion as a discrepancy between physical stimulus and percept (here referred to as illusion_d, as long as merely this "error" is meant) is unable to capture the four very different cases in which illusions can arise. The observer may or may not be aware of the discrepancy, and its magnitude may be large or small. I argue that the special case of small error paired with awareness deserves special attention. Only in this case does the observer readily see the illusion, since it becomes manifest (referred to as illusion_m). Illusion_m is a meaningful category even in cases where illusion_d cannot be determined. Illusions_m of apparent motion and illusions of intuitive physics are solicited.