Somnambulism

Somnambulism, numbness, hypnosis, amputation, and the Narcissus trance all refer to the fact that of everyone who is deeply affected by media, very few of them are aware of that effect the media is having on them.

Somnambulism is particularly a response to hot media. The intensity of their high-definition data means that the experience must be "cooled" before it can be accepted. This is even more so the case during periods when such media are new.

In Greek mythology, Narcissus saw a reflection of himself in the water and mistook it for another person. Becoming enthralled by the image, his perceptions were numbed until he became inexorably tied to the reflection. McLuhan interprets the myth to refer to how people become fascinated by any extensions of themselves. By emphasizing that the myth does not hint that Narcissus saw the reflection as himself, but rather as another person, McLuhan emphasizes that it is any extension of ourselves that can have the same effect.

The process of amputation or numbness is illustrated in the response of the central nervous system to superstimulation. The central nervous system protects itself by amputating or numbing whichever sense or organ is overstimulating it. This is analogous to how the central nervous system responds to all media, which are extensions of various human faculties. At times, only the offending sense is numbed, but at other times the numbness extends across all senses.

The major effect of amputation of senses is closure, or a change in sense rations.

With electric technology, which extends the central nervous system itself, the principle of numbness still applies.

Examples
The wheel:
 * Money arose as a form of exchange of goods
 * This resulted in an acceleration of the exchange of goods.
 * As a result, the wheel arose as an extension of the foot
 * The wheel amplifies the function of the feet, being more effective
 * The nervous system responds with a numbness toward the wheel, an amputation of it from the body

Remedies
McLuhan writes that the only way to be able to understand media is to remove oneself from under the assumptions and values imposed by those media. This is difficult to do, because the effect can happen immediately upon contact with the medium.