Perception is a psychological process, capable of gathering individual characteristics of phenomena, reflected by the senses in an objective, unified, and complete way. Perceptual disorders are common, they always signal a pathology of the nervous system.

Human cognition is a complex process, going from sensory to rational cognition. Cognition includes sensation, perception, symbol, thinking, judgment, reasoning... In which, perception is the reflection of human consciousness with a unified, complete objective thing, this is a higher reflection than sensation.

Hallucinations/delusions come in many forms, but they all have one thing in common: people affected by the condition cannot be sure that some of the things they believe are not true. These unchangeable beliefs are different for each person and affect different parts of their lives.