If anything can be said to exist, there is a philosopher prepared to debate its existence. Likewise in neuroscience, amusements become canonical, as in the website featuring the drawing above, and someone will step up to tell its cultural history,neurophysiology, research through twelve orders of magnitude and much else besides.
Sensory illusions, ambiguous figures, are magic acts the Great Embodied Embedded Brain performs every second. Any theory of brain functioning has to accept these as touchstones – provide a testable hypothesis and your theory is real gold, otherwise, the other kind.
This site is a labor of love – literally an amateur – production about illusions and ambiguous figures. It is lovely – like a great mansion of dreams where once we enter we are compelled to wander from room to room. I am haunted by visual illusions. My first experiments – unsuccessful because the hypothesis was ill posed – embraced them. I was nine years old. Alas, this beautiful memory is only a shadow.