What is a Hallucination? - Definition, Causes & Types

Lesson Transcript
Instructor: Sarah Lavoie

Sarah has taught Psychology at the college level and has a master's degree in Counseling Psychology.

Hallucinations can be caused by several things, including sleep deprivation and a variety of diseases. Learn the definition of a hallucination and the different types of hallucinations, including hypnagogic, hypnopompic, visual, auditory, olfactory, haptic, and gustatory. Updated: 09/09/2021

Understanding Perception

At quick glance, what is the image in this picture?

When looking at this image, you're using your sense of sight to perceive what is there. So, is this an image of a vase, or is it two people facing each other? Which did you see first?

We become aware of and identify what is going on around us through our perceptions. Unfortunately, the five senses do not give us the whole picture. Tasting, hearing, smelling, feeling, and seeing are only the beginning of the sensory process. Although two people may be confronted with the same experience or stimulus, it's common for them to process the information differently.

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  • 0:01 Understanding Perception
  • 0:40 What Is a Hallucination?
  • 2:20 Causes of Hallucinations
  • 3:14 Lesson Summary
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What Is a Hallucination?

A hallucination is different than an illusion like the one above. Illusions are common misinterpretations of a stimulation to the senses. Hallucinations are misinterpretations in the absence of a sensory stimulus.

Most people have experienced seeing, hearing, and feeling things in the state between wakefulness and sleep. The hallucinations that occur upon awakening are called hypnagogic hallucinations. Those seen while falling asleep are called hypnopompic hallucinations. Neither are preceded by stimulation to one of the senses, but both are completely normal.

Although we may immediately associate seeing things with hallucinations, visual hallucinations are not the most common type of hallucination. Auditory hallucinations, such as hearing voices, are the most common. But hallucinations can occur with any of the senses, or even a combination of senses. Here are some other types of hallucinations:

  • Olfactory hallucinations: smelling things that aren't there
    Jane looks around because she smells smoke. She searches for the source of the smell, as it gets stronger and stronger. But there is no fire.
  • Haptic hallucinations: feeling things that aren't there
    John sits at his mother's dining room table. He's fascinated by how the tablecloth feels like velvet, and he continues to rub his hand over it to feel the fibers. The tablecloth is cool, smooth plastic.
  • Gustatory hallucinations: tasting things that aren't there
    Jane is driving home from work. To her surprise, as she gets closer to home, she begins to taste pickles from her grandmother's secret recipe.

Causes of Hallucinations

Psychologists are certain that physiology of the brain plays a role in hallucinations. Patients who previously report hallucinations often have lesions that are located in areas of the brain responsible for the type of hallucination they experienced. Various injuries, illnesses, genetic disorders, and certain drugs can induce hallucinations in people.

Here's a list of some other causes of hallucinations:

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