How the Mind Works - michaeljgoodnight.com

The Mind's Eye j 259
Is a nose an object? Is a head one? Is it still one if it is attached to a body?
What about a man on horseback? These questions show that the difficulties
in trying to formulate what should be recovered as a region from an
image are so great as to amount almost to philosophical problems. There
is really no answer to them—all these things can be an object if you want
to think of them that way, or they can be part of a larger object.
A drop of Krazy Glue can turn two objects into one, but the visual system
has no way of knowing that.
We have, however, an almost palpable sense of surfaces and the
boundaries between them. The most famous illusions in psychology
come from the brain's unflagging struggle to carve the visual field into
surfaces and to decide which is in front of the other. One example is the'
Rubin face-vase, which flips between a goblet and a pair of profiles tetea-tete.
The faces and vase cannot be seen at the same time (even if one
imagines two men holding up a goblet between their noses), and
whichever shape predominates "owns" the border as its demarcating line,
relegating the other patch to an amorphous backdrop.
D
Another is the Kanisza triangle, a stretch of nothingness that blocks out a
shape as real as if it had inscribed it in ink.
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V ~7
The faces, vase, and triangle are familiar objects, but the illusions do not
depend on their familiarity; meaningless blobs are just as compelling.
I