Perception is based on certain factors of organization,
including the figure-ground relationship. Another factor is the
wholeness of figures (determined by symmetry, closure, and
familiarity). A third is the grouping of elements (based on
proximity, similarity, continuation, and common fate). Three
other factors importantly involved in perception include
attention, variations in stimulus input, and the constancies
(shape, size, brightness, and color).
"Errors" in perception occur when the constancies fail.
The resulting illusions are of four types -- straight-line,
bisecting or orientation, compound straight-line, and figure.
Such information can be applied in designing clothing to create
specific impressions. Subliminal perception is feared more than
is warranted. Extra-sensory perception remains controversial
and is still lacking in hard scientific proof.