They aren´t deaf but not listen
The physiological fact of listening can be in contrast with the apprehension of the content in the human brain, that is, one can have a suitable hearing aid or even artifacts that help, but even listening, do not listen, that is, they do not apprehend the content.
McLuhan’s view that communication as a medium tends to be defined as transparent, innocuous, unable to determine what are the communicative contents that are conveyed.
Its only effect on the artifact, whatever it was, in the communication process would be negative, due to noises or obstacles in the delivery of the message, this was already the preoccupation as a device of Claude Shannon, but now McLuhan calls either the message made orally or in writing, be it transmitted by radio, television, puts in play new structures being artifacts intended to broaden the senses highlighting contours and other nuances of what is communicated, in this work relates to the artist who wishes to highlight something.
Put more directly, for McLuhan, the medium, the cane (terms more appropriate for Shannon), the technology artifacts that communication establishes, is not only a form of communication, but will ultimately determine the own content.
What McLuhan points out is the fact that a message delivered both orally as in writing, when broadcasting on the radio or television sets the content.
Their central thesis is that there is a double operation: 1) to study the evolution of the communal media used by men throughout their history, and 2) to identify the specific characteristics of each of these different media / communication artifacts .
These are two central points of his investigation that are at the root of one of his fundamental works, namely Understanding Media, of 1964.
Thus develops three galaxies, when only one is remembered, the Gutenberg Galaxy, which is typical of the written culture and then printed with the possibilities of reproducibility, but there is the oral or acoustic cultural that is previous, where the question of listening is fundamental (orally speaking), oracles and prophets occupy a central role, and the present one that McLuhan called electronic, but it is possible as an extension to speak of a digital galaxy in network, where there are media of networks that do not must be confused with the networks, since they exist in the previous galaxies.
So those who are trapped in the Gutenberg galaxy do not listen to oral culture, and those who are trapped in the culture of pure technology do not listen to oral and written culture