Manifest illusions : a reply to Axel Kohler

Abstract

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.