The term illusion refers to a specific form of sensory distortion. Unlike a hallucination, which is a distortion in the absence of a stimulus, an illusion describes a misinterpretation of a true sensation. While illusions distort reality, they are common in most people. The most common illusions are:
- Visual (optical illusion)
- Tactile (touch)
- Olfactory (smell)
Visual illusions (optical illusions), are the most well known and understood. The emphasis on visual illusions occurs because vision often overpowers the other senses. One example is watching a ventriloquist. We perceive the voice is coming from the dummy since we are able to see the dummy mouth the words.
Mimes create illusions that are created by physical means. The mime creates an illusion of acting upon or being acted upon by an unseen object. Well known examples include “walls”, “climbing stairs”, “leaning”, “descending ladders”, “pulling and pushing” etc. An optical illusion is always characterized by seeing a real image but the perceived images are deceptive or misleading.
Move your head forward and backward. As your head moves closer to your monitor and then back away from your monitor, the circles will appear to be spinning. But are they really spinning? Absolutely NOT!
The horizontal grey bar is the same shade throughout
Is it a face or a vase?
An auditory illusion is an illusion of hearing, the sound equivalent of an optical illusion: the listener hears either sounds which are not present in the stimulus, or “impossible” sounds. For example, hearing voices regardless of the environment would be a hallucination, whereas hearing voices in the sound of running water (or other auditory source) would be an illusion.
An example of tactile illusions is a phantom limb. A phantom limb is the sensation that an amputated or missing limb (even an organ, like the appendix) is still attached to the body and is moving appropriately with other body parts. Approximately 50 to 80% of individuals with an amputation experience phantom sensations in their amputated limb, and the majority of the sensations are painful. Phantom sensations may also occur after the removal of body parts other than the limbs, e.g. after amputation of the breast, extraction of a tooth (phantom tooth pain) or removal of an eye (phantom eye syndrome). The missing limb often feels shorter and may feel as if it is in a distorted and painful position. Occasionally, the pain can be made worse by stress, anxiety and weather changes. Phantom limb pain is usually intermittent. The frequency and intensity of attacks usually decline with time
Illusions can occur with the other senses including that of taste and smell.
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