The reason being, McLuhan tells us, is that media are an extension of our senses, and are thereby organised by patterns of sensory perception. A crucial aspect of McLuhan's theory is his emphasis on the interplay between the senses and media technology. Media are not described as being separate from the body, in fact the body and media technology are described as being enmeshed and interactive. They are linked integrally, since the origin of media, as McLuhan regards it, is the extension of the nervous system and the senses beyond the body. In relation to the way we experience media, McLuhan identifies different media as falling into categories of hot or cool forms.
High definition is the state of being well filled with data.
This means that the message of the medium is very defined and complete, resulting in a low-level of sensory participation with the medium. Alternatively, a cool medium is low in definition and data, involving more sensory participating with the medium to complete its meaning. The television is a good example of a cool medium, as it projects a mosaic of light particles onto the spectator, engaging the spectator in a tactile experience of the medium. The physical participation in the reception process is also heightened by the necessity to order the light mosaic into a coherent form, which involves the senses further in completing the image. Because of the high level of sensory participation, a cool medium is more inclusive of the senses than a hot medium.