McLuhan's distinction between hot and cold media seems straightforward. Hot media exclude, and are low in participation, whereas cool media include and call for greater participation. A photograph, for example, is high definition or hot; whereas a cartoon is low definition or cool because the rough outline drawing provides very little visual data and requires the viewer to fill in or complete the image himself.14
But McLuhan is applying these distinctions at a time when television was still largely monochrome and picture quality was poor, so he holds that television is a cool medium because it renders images in a cartoon-like way. The telephone, which gives the ear relatively little data, is cool, as is speech; both demand considerable filling in by the listener. On the other hand, radio is a hot medium because it sharply and intensely provides great amounts of high-definition auditory information that leaves little or nothing to be filled in by the audience.
It is unfortunate that, being based in Canada, McLuhan was unable to experience the BBC's Goon Show which revolutionised comedy by exploiting the way listeners' imaginations have to flesh-out the cool suggestions of the radio. For all its technological pointillism, television has become much hotter since McLuhan's time and it gives many couch potatoes a sensation of sinking into a passive state while images force themselves into the consciousness, usually accompanied with musical effects to manipulate our value judgements. In The Fall of Public Man Richard Sennet appears to take issue with McLuhan and says of television: "Its terms are comparable to the technology of modern construction: one sees more and interacts less."15
The closest most television viewers get to interacting with television's coolness is by channel-hopping, or choosing to switch the thing off. And for the most part it is only by retrospectively surveying representative samples of viewers, to gather ratings, that television networks are able to respond to the market. At the same time radio has further cooled with the rise of the phone-in talk show, and the BBC Radio 4's Today Programme calling on listeners to e-mail suggested questions before interviewing representatives of the Russian government.16
But aside from this apparent anomaly, the terms hot and cold serve well to denote relative capacity for interactivity in a given medium.