Hallucinations (psychology)

• TYPE OF PSYCHOLOGY: Consciousness; psychopathology
• Hallucinations are unusual perceptual phenomena that cause a person to experience imaginary perceptions as reality. There are several different types of hallucinations, and they can result from several different causes.

Introduction

Hallucinations are defined as sensory experiences that occur in the absence of sensory stimulation. Hallucinations, therefore, are false perceptions. There are five major types of hallucinations, which correspond with the five senses.

Visual hallucinations occur when a person sees something that is not there, such as a person whom others do not see. They often involve the false perception that one sees God, the devil, or a meaningful person in one’s life. Visual hallucinations are usually reported to appear in black and white. They can be very frightening for the individual experiencing them. An individual initially may be reluctant to tell others about these visual phenomena. Auditory hallucinations are more common than visual hallucinations and refer to the phenomenon of hearing things that others do not hear, such as voices that seem to be coming from the person’s own mind. Tactile hallucinations correlate with the sense of touch and involve the perception of feeling things that are actually not present. The mistaken perception that bugs are crawling down one’s arm is an example of a tactile hallucination. The insistence that one feels two strands of hair in one’s eye is another example of a tactile hallucination. Gustatory hallucinations involve the false perception of tasting things that are not present, such as experiencing an imaginary metallic taste in one’s mouth. Olfactory hallucinations involve smelling things without stimuli to create such smells, such as the smell of burning flesh.

Though much less common, some individuals experience presence hallucinations, which involve the feeling of another person being in the room when no such person exists. Proprioceptive hallucinations involve the feeling of one's arms or legs moving or feeling separate from the body. Some people are more likely to experience hallucinations upon waking, Hypnopompic hallucinations, and others experience hallucinations more frequently when falling asleep, called Hypnagogic hallucinations.

A hallucination is a perceptual experience that differs from the occasional mistaken perception, such as the belief that one’s name has been called or that one has seen a friend or acquaintance across the street. Instead, a hallucination is believed by the person to be real, despite repeated evidence to the contrary. Individuals experiencing hallucinations will insist vehemently on the existence of such stimuli and will reject explanations that suggest they are mistakenly perceiving something. (If an individual experiences a hallucination but recognizes that it is not real, it is called a pseudohallucination instead.) Hallucinatory behavior is often recurrent.

Hallucinations are altered states of consciousness or awareness and can result from several different causes. They may be caused by changes in neurological stimulation, such as a high fever, delirium, or epileptic seizure. Different somatic, or bodily, states may foster the development of hallucinations. For example, the effects of starvation, oxygen deprivation, sleep deprivation, or a heightened state of awareness can increase the likelihood of hallucinating. Hallucinations also may be a symptom of a psychological disorder such as schizophrenia or major depression. Hallucinations may be induced with psychoactive substances, such as hallucinogenic drugs.

Schizophrenic Hallucinations

Schizophrenia is a mental disorder characterized by a loss of contact with reality and the presence of psychotic behaviors, including hallucinations and delusions. Symptoms of schizophrenia are classified as positive or negative; positive symptoms of schizophrenia refer to behavioral excesses, whereas negative symptoms refer to behavioral deficits. Examples of positive symptoms of schizophrenia include hallucinations, delusions, and disorganized speech. Negative symptoms include the neglect of one’s hygiene, social withdrawal, and a flattening of one’s emotions.

The most commonly experienced hallucinations among schizophrenic patients are auditory. Patients with schizophrenia often report hearing voices commenting on their behavior. Others will report hearing voices that are arguing with each other. Some with schizophrenia state that the voices they hear are insulting and antagonistic toward them. The voices may be of either gender. Command hallucinations are hallucinations that involve voices that order one to do something, such as cause harm to oneself or others. Research has suggested that individuals with command hallucinations are more likely to obey a command hallucination if they recognize the “voice” issuing the command. These perceptual experiences can be very distressing. A person who has schizophrenia may feel plagued by the voices. An individual experiencing chronic auditory hallucinations may wear headphones in a desperate attempt to stop the perceived voices. It is typical for the individual experiencing auditory hallucinations to experience depression.

Schizophrenia is also characterized by the presence of delusions, or false beliefs that persist despite contrary evidence. Delusions might involve the false and persistent belief that one is being followed or poisoned or that one’s thoughts are being broadcast for others to hear. They often develop due to an effort by the individual to explain their hallucinations. Individuals who experience frequent auditory hallucinations may develop the delusion that others are plotting against them and are lying when they say that they do not hear the hallucinatory voices.

The auditory areas in the brain's temporal lobes are associated with hearing ability. Stimulation of these parts can create a false perception of sound. Magnetic resonance imaging (MRI) scans of the brains of people with schizophrenia who experience auditory hallucinations reveal activity in the auditory centers of the brain even when no external sound has stimulated that brain region. Research has suggested that patients who report hearing voices may be unable to distinguish their internal thoughts from external stimuli. Therefore, an individual experiencing auditory hallucinations may be attributing internally generated thought processes to an external source. This research, however, fails to offer plausible explanations for the occurrence of visual, tactile, olfactory, or gustatory hallucinations.

Schizophrenic patients are often treated with antipsychotic medications to alleviate the psychotic symptoms they experience. In the 1930s and 1940s, French chemists developed a group of medications called phenothiazines. The phenothiazines were found to be effective in decreasing positive symptoms among schizophrenic patients, such as hallucinations and delusions, but they also carried the risk of serious side effects. In the 1980s, new antipsychotic drugs known as atypical antipsychotics were found to be effective in treating both the positive and the negative symptoms of schizophrenia with fewer side effects than phenothiazines. Clozapine, risperidone, and olanzapine are some of the atypical antipsychotics that became increasingly popular in the 1990s. These drugs have been especially successful in treating schizophrenia symptoms such as hallucinatory experiences. Research studies have suggested that cognitive behavior therapy (CBT) is effective in treating schizophrenic patients who experience hallucinations and delusions.

Drug-Induced Hallucinations and Delirium

Certain psychoactive drugs (substances that affect the brain’s functioning) can induce hallucinatory experiences. Hallucinogens are a class of psychoactive substances that include lysergic acid diethylamide (LSD), psilocybin, ecstasy, and mescaline. All these drugs are powerful and potentially dangerous substances that have proved harmful to many who have ingested them in a recreational context.

LSD gained notoriety during the 1960s. Harvard University professor Timothy Leary was an influential advocate for the use of LSD, touting its ability to induce greater self-awareness. LSD is a powerful hallucinogen that is odorless and tasteless. After using the drug, the individual will experience about eight hours of altered perception, accompanied by mood changes and other symptoms. Psilocybin, another hallucinogen, is found in certain types of mushrooms. Psilocybin is a less potent hallucinogen than LSD and has for centuries been considered sacred by the Aztecs in Mexico and Central America. Methylenedioxymethamphetamine (MDMA), more commonly known as ecstasy, stimulates the central nervous system, resulting in hallucinogenic experiences. Mescaline is a hallucinogen derived from a cactus plant called the peyote. For hundreds of years, Native Americans have used peyote during religious ceremonies to facilitate and intensify spiritual experiences.

Much of what is known about the hallucinatory experiences of people who use hallucinogens is derived from their first-person reports. Hallucinogens usually induce colorful, vivid images in the initial stages of use. These hallucinations may include images of places, scenes, people, or animals. Some hallucinatory experiences are reported to be pleasant, and sometimes inspiring, perceptual experiences. Individuals who use hallucinogens are frequently searching for a spiritual transcendence. Others who have used these substances report a “bad trip,” or a hallucinatory experience that was unpleasant or frightening and could lead to panic attacks and heightened anxiety. Heavy use of stimulant drugs, such as cocaine and amphetamines, can also cause frightening hallucinations and delusions. Marijuana may produce mild hallucinatory effects because it enhances sensory experiences. Hallucinations can also be a withdrawal symptom from alcohol dependence.

Delirium is a mental state characterized by a clouding of consciousness in which a person may seem confused and disorganized. The symptoms of delirium have a rapid onset and include difficulty in maintaining or shifting attention, disorientation, and, at times, the presence of visual and tactile hallucinations. There are many possible causes of delirium, including metabolic disease, infection, endocrine disease, and side effects of certain medications, and treatment involves identifying and then treating the source.

Sleep deprivation seems to alter people’s perceptions of their surroundings and can also produce mild hallucinations. Research suggests that hallucinations have been reported among subjects who were deprived of sleep for sixty hours.

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