Sensation and Perception and Effects of Drugs

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Every behavior in which an organism engages involves information from the primary senses, such as vision, hearing (audition), and touch. A number of drugs of abuse alter sensory information. Mind-altering drugs can also influence perception of time, thinking, behavior, and mood. Often abusers of these drugs experience severe depression, anxiety, paranoia, confusion, and terror.

Naturally occurring drugs, such as Mescaline from the Peyote cactus, increase awareness of visual and auditory sensations and also produce visual illusions and Hallucinations. The Psilocybin mushroom (Mexican or Magic mushroom) produces similar effects. Because of these sensory changes, mescaline and psilocybin have been used since pre-Columbian times in religious ceremonies by the peoples of Mexico and the American southwest.

Lysergic Acid Diethylamide (LSD), an artificially-produced drug which was first synthesized in the late 1930s by the Swiss chemist Albert Hoff-mann, has become well known for producing intense and colorful visual sensations. People also report changes in sensory behavior with drugs that are related to LSD (such as DMT, DOM, and MDMA, also known as "ecstasy" or the "love drug"). DMT is a short-acting (cycle takes less than one hour) crystalline powder that produces visual hallucinations. DOM, also known as STP, is more than 50 times as potent as mescaline. MDMA produces "out-of-body" sensations and acts as a stimulant. Phencyclidine (PCP) is another synthesized drug that is sometimes added to the list of drugs that alter sensory behavior; however, its sensory effects are limited to numbness in the hands and feet. Ketamine, also known as Special K, is a veterinary medicine that is chemically similar to PCP; its effects range from delirium to inability to move.

The active constituent of marijuana, Tetrahydrocannabinol (THC), also produces alterations in sensory behavior; however hallucinationssuch as those produced by mescaline or LSDare less common with THC, although there is an increased risk of psychotic symptoms among users with a family or personal history of psychosis. Cocaine and Amphetamine sometimes produce hallucinations and other sensory distortions, but only when they are taken for long periods of time.

Various names are used to describe drugs that alter sensory behavior. One term is psychedelic, which refers to mind-expansion or to experiencing events that go beyond normal boundaries; this word was coined in 1956 by Humphrey Osmond, a British psychiatrist. Another term is psychotomimetic, which refer to the similarities of hallucinations that occur in psychotic disorders, such as Schizophrenia, and those produced by mescaline and LSD. The term hallucinogenic is slightly misleading, since not all drugs that alter sensory behavior produce hallucinations.


Most of our information about drugs and the ways in which they alter sensory behavior in people comes from individual reports (called anecdotal) rather than from well-controlled laboratory studies. People have reported vivid images, changes in perception, and hallucinations after they have taken mescaline or LSD. Synesthesiasa mixing of the senses, such as "the hearing of colors" or "the seeing of sounds"may also occur. One of the first descriptions of LSD's effects is recounted as follows:

I was seized by a peculiar sensation. Objects, as well as the shape of my associates in the laboratory, appeared to undergo optical changes. With my eyes closed, fantastic pictures of extraordinary plasticity and intensive color seemed to surge toward me. After two hours this state gradually wore off (Julien 180).

Although these sensory disturbances stop within a few hours, some people experience confusion, sensory distortions, or poor concentration for longer periods of time. For some people, drug effects recur long after the drugs have left their systemsthese brief episodes are called flashbacks.


Since alterations in sensory behavior, such as hallucinations, cannot be observed directly, it is very difficult to examine these effects in laboratory animals. One way to investigate a drug's effect on sensory behavior is to train animals to behave differently in the presence of different types of visual or auditory stimuli. If a drug changes the animal's behavior, it is possible that these changes in behavior are due to a change in how well the animal hears or sees the stimuli. Another type of procedure examines how intense (e.g., how loud or how bright) a stimulus has to be for an organism to hear or see it. In these procedures, the intensity required to hear or see a stimulus is determined before a drug is given and then it is compared to the intensity required to hear or see the stimulus after the drug is given.

In general, drugs such as mescaline, LSD, and THC do not alter an animal's ability to tell the difference between visual or auditory stimulinor do they alter visual or auditory thresholds. This lack of effect in animals suggests one of two explanations: either drugs such as LSD produce different effects in animals than they do in people, or, more likely, the procedures that are used to study alterations in sensory behavior in animals do not measure the unique ways in which drugs such as LSD alter sensory behavior.

Conversely, MDMA testing has found comparable results in both animals and humans. A late 1990s study (conducted on red squirrel monkeys) at Johns Hopkins University showed that MDMA has damaging effects on memory. Published in 2000, a British study of both current and previous MDMA users has discovered both immediate and delayed memory deficits.

(See also: Complications ; Inhalants ; Opiates/Opioids ; Research ; Research, Animal Model )


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Linda Dykstra

Revised by Rebecca Marlow-Ferguson