Hallucination, comparable to daydreaming, can be defined as the experience of a sensory perception in the absence of an appropriate stimulus; however, this experience has the force of a real perception and gives the feeling of being related to an external event rather than being a product of imagination. Therefore, it is difficult to distinguish hallucination from reality. What is seen in hallucination appears to have the character of objectivity, that is, it appears to be independent of the will and desires of the subject, who believes that anyone else can share and confirm that experience. Hallucination is thus distinguished from delusion in that the latter is simply a misinterpretation of a normal sensory stimulus. Hallucination, in essence, is created by the subject’s mind, while delusion comes from an external stimulus that is misinterpreted by the mind.
Altered states of consciousness – Hallucinations are predominantly visual or auditory, but can also affect touch, smell or taste. They are typical of mental illnesses such as schizophrenia, as well as various forms of epilepsy. However, even healthy people can experience hallucinations; in addition to those found in the intermediate state between sleep and wakefulness (so-called hypnagogic and hypnopompic hallucinations, which were alluded to in the article Dreams), hallucinations occurring under conditions of fatigue or stress or in the presence of altered states of consciousness are common. The latter, which occur when psychic activity takes place abnormally, may be due to alcohol or drug use, to excessive prayer or meditation with obsessive repetition of words or phrases, to hunger and thirst or sleep deprivation, to strenuous physical movements such as uninterrupted dancing or prolonged running, but also to an absence of sensory stimuli, as for a hermit in the desert, or conversely to an excess of such stimuli, especially of the acoustic kind, for example continuous ritual drumming. It will be noted that all these situations correspond to the methods used for millennia now by holy men, ascetics, sorcerers, and shamans to “see spirits” and establish contact with the supernatural. Virtually all the various visions and apparitions of religious, magical and paranormal traditions can be traced back to hallucinations due to altered states of consciousness.
Illusions – To the field of illusions, on the other hand, belongs pareidolia, which is a misperception in which from a vague or obscure stimulus a well-defined sensation, usually visual or auditory, is drawn. This is the case, for example, when one sees a human face on the full moon or when one discovers various objects or figures in the shape of clouds or constellations. The phenomenon can be traced to the fact that our brains are accustomed, not to say obliged, to recognize shapes. In the chaos of sensory stimuli we have to identify very specific figures, colors, sounds, movements in order to orient ourselves in the world and figure out how to act within it. Our brain does not tolerate chaos, so even in an indistinct stimulus we tend to recognize something, to find meaning in ambiguity, and what we recognize is influenced by our knowledge, beliefs and convictions.