McLuhan’s central suggestion is that all human experience may be studied as situated within a “unified field” of different patterns of “homeostasis of the perceptual factors” — aka different patterns of “relative interplay of the optical and the auditory modes” as modulated by touch. These patterns, in turn, may be characterized as different forms of “distribution of emphasis [or stress] among the senses“.

Gutenberg Galaxy 63
The increase of visual stress among the Greeks alienated them from the primitive art that the electronic age now reinvents after interiorizing the unified field of electric all-at-oneness.

Gutenberg Galaxy 71
“For religious man, space is not homogeneous; he experiences interruptions, breaks in it”
(Eliade). Likewise in time. For the modern physicist, (…) space is not homogeneous, nor is time. By contrast, the geometrical space invented in antiquity, far from being diverse, unique, pluralistic, sacral, “can be cut and delimited in any direction; but no qualitative differentiation and, hence, no orientation are given by virtue of its inherent structure.” (Eliade) The next statement applies entirely to the relative interplay of the optical and the auditory modes in the shaping of human sensibility: “It must be added at once that such a profane existence is never found in the pure state. To whatever degree he may have desacralized the world, the man who has made his choice in favor of a profane life never succeeds in completely doing away with religious behavior. This will become clearer as we proceed; it will appear that even the most desacralized existence still preserves traces of a religious valorization of the world.” (Eliade)

McLuhan to Chuck Bayley, December 16, 1964 (Gordon 150)
His [Innis’] great insight was that every situation can be studied structurally by asking the question: ‘What is the primary stress or action that holds this whole structure in place?’ I think he got this approach from Max Weber. Weber had used it for institutions. Innis extended the approach to media. This structural approach tends to dispense with the accidents of ‘content’.

MM to Hans Selye, July 25, 1974 (Gordon 150)
My own approach (…) is a transformation theory, thus homeostasis of the perceptual factors in a rapidly changing environment requires much redistribution of emphasis among the senses. For example, a blind or deaf person compensates for the loss of one sense by a heightening of activity in the others.  It seems to me that this also occurs in whole populations when new technologies create new sensory environments.