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.
Two types of consciousness are considerable regarding perception: phenomenal (any occurrence that is observable and physical) and psychological. The difference everybody can demonstrate to him- or herself is by the simple opening and closing of his or her eyes: phenomenal consciousness is thought, on average, to be predominately absent without sight. Through the full or rich sensations present in sight, nothing by comparison is present while the eyes are closed. Using this precept, it is understood that, in the vast majority of cases, logical solutions are reached through simple human sensation. 
The analogy of Plato's Cave was coined to express these ideas.
Passive perception (conceived by René Descartes) can be surmised as the following sequence of events: surrounding → input (senses) → processing (brain) → output (re-action). Although still supported by mainstream philosophers, psychologists and neurologists, this theory is nowadays losing momentum. The theory of active perception has emerged from extensive research of sensory illusions, most notably the works of Richard L. Gregory. This theory, which is increasingly gaining experimental support, can be surmised as dynamic relationship between "description" (in the brain) ↔ senses ↔ surrounding, all of which holds true to the linear concept of experience.