hallucination hallucination a hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. hallucinations are vivid, substantial, and are perceived to be located in external objective space. hallucination is a combination of two conscious states of brain wakefulness and rem sleep. they are distinguishable from several related phenomena, such as dreaming (rem sleep), which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus (i.e., a real perception) is given some additional significance. many hallucinations happen also during sleep paralysis. hallucinationmy eyes at the moment of the apparitions by august natterer, a german artist who created many drawings of his hallucinationsspecialtypsychiatry hallucinations can occur in any sensory modality—visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive. hallucinations are referred to as multimodal if multiple sensory modalities occur. a mild form of hallucination is known as a disturbance, and can occur in most of the senses above. these may be things like seeing movement in peripheral vision, or hearing faint noises or voices. auditory hallucinations are very common in schizophrenia. they may be benevolent (telling the subject good things about themselves) or malicious, cursing the subject. 55% of auditory hallucinations are malicious in content, for example, people talking about the subject, not speaking to them directly. like auditory hallucinations, the source of the visual counterpart can also be behind the subject. this can produce a feeling of being looked or stared at, usually with malicious intent. frequently, auditory hallucinations and their visual counterpart are experienced by the subject together. hypnagogic hallucinations and hypnopompic hallucinations are considered normal phenomena. hypnagogic hallucinations can occur as one is falling asleep and hypnopompic hallucinations occur when one is waking up. hallucinations can be associated with drug use (particularly deliriants), sleep deprivation, psychosis, neurological disorders, and delirium tremens. the word "hallucination" itself was introduced into the english language by the 17th-century physician sir thomas browne in 1646 from the derivation of the latin word alucinari meaning to wander in the mind. for browne, hallucination means a sort of vision that is "depraved and receive its objects erroneously". classification hallucinations may be manifested in a variety of forms. various forms of hallucinations affect different senses, sometimes occurring simultaneously, creating multiple sensory hallucinations for those experiencing them. auditory auditory hallucinations (also known as paracusia) are the perception of sound without outside stimulus. auditory hallucinations can be divided into elementary and complex, along with verbal and nonverbal. these hallucinations are the most common type of hallucination, with auditory verbal hallucinations being more common than nonverbal. elementary hallucinations are the perception of sounds such as hissing, whistling, an extended tone, and more. in many cases, tinnitus is an elementary auditory hallucination. however, some people who experience certain types of tinnitus, especially pulsatile tinnitus, are actually hearing the blood rushing through vessels near the ear. because the auditory stimulus is present in this situation, it does not qualify it as a hallucination. complex hallucinations are those of voices, music, or other sounds that may or may not be clear, may or may not be familiar, and may be friendly, aggressive, or among other possibilities. a hallucination of a single individual person of one or more talking voices is particularly associated with psychotic disorders such as schizophrenia, and hold special significance in diagnosing these conditions. in schizophrenia voices are normally perceived coming from outside the person but in dissociative disorders they are perceived as originating from within the person, commenting in their head instead of behind their back. differential diagnosis between schizophrenia and dissociative disorders is challenging due to many overlapping symptoms, especially schneiderian first rank symptoms such as hallucinations. however, many people who do not have a diagnosable mental illness may sometimes hear voices as well. one important example to consider when forming a differential diagnosis for a patient with paracusia is lateral temporal lobe epilepsy. despite the tendency to associate hearing voices, or otherwise hallucinating, and psychosis with schizophrenia or other psychiatric illnesses, it is crucial to take into consideration that, even if a person does exhibit psychotic features, they do not necessarily have a psychiatric disorder on its own. disorders such as wilson's disease, various endocrine diseases, numerous metabolic disturbances, multiple sclerosis, systemic lupus erythematosus, porphyria, sarcoidosis, and many others can present with psychosis. musical hallucinations are also relatively common in terms of complex auditory hallucinations and may be the result of a wide range of causes ranging from hearing-loss (such as in musical ear syndrome, the auditory version of charles bonnet syndrome), lateral temporal lobe epilepsy, arteriovenous malformation, stroke, lesion, abscess, or tumor. the hearing voices movement is a support and advocacy group for people who hallucinate voices, but do not otherwise show signs of mental illness or impairment. high caffeine consumption has been linked to an increase in likelihood of one experiencing auditory hallucinations. a study conducted by the la trobe university school of psychological sciences revealed that as few as five cups of coffee a day (approximately 500 mg of caffeine) could trigger the phenomenon. visual