If perceptions are made without the presence of a real object or cause, we speak of a hallucination, which is distinguished from an illusion by the fact that the illusion has an existing object or cause of sense perception, which is assumed to be alienated. The affected person believes the hallucination to be reality. There are hallucinations that involve auditory, kinesthetic, visual, olfactory, and gustatory perception - all of our sensory channels. In semi-sleep or during a change to or from the sleep state, we speak of hypnagogic hallucinations. These are very similar to those in the state of hypnosis and during meditation. When we speak of negative hallucinations, we are referring to blanked out perceptions of reality during the trance.