The gulping or swallowing of Nature by the machine was attended by a complete change of the ground rules of both the sensory ratios of the individual nervous system and the patterns of the social order as well. (Notes on Burroughs, 1964)

in the age of the X-ray inner and outer are simultaneous events.  (Through the Vanishing Point, 254)

According to Philip Marchand in his bio of McLuhan, The Medium and the Messenger:

In ‘Footprints in the Sands of Crime’ McLuhan (…) articulated a theme that would remain his until the end of his career — the theme of Poe’s story “The Maelstrom.” In that story, a sailor caught in a giant whirlpool eventually saves himself from drowning through detached observation of the vortex. For McLuhan, the sailor’s action became a symbol, along with the sleuth, of his own work — of his freeing himself from the vortex of threatening social change through the process of understanding it. (McLuhan never mentioned that the hero of the story was broken in mind and body after the experience.)¹

Marchand’s description here goes fundamentally awry. For, in the first place, McLuhan did indeed see “that the hero of [Poe’s] story was broken in mind and body” — to the point of “vanishing”:

Managing The ‘Ascent’ from the Maelstrom² today demands awareness that can be achieved only by going Through the Vanishing Point. (Take Today, 13)³

More importantly, Marchand’s take on McLuhan’s appeal to the Maelstrom is that it concerns a “hero” who “saves himself (…) through detached observation” of “the vortex of threatening social change”. But such a stable heroic identity, however broken it might become, with an objective perspective on an exclusively external social environment, is possible only within the parameters of the Gutenberg galaxy!  As McLuhan repeatedly maintained:

From the development of phonetic script until the invention of the electric telegraph human technology had tended strongly towards the furtherance of detachment and objectivity, detribalization and individuality. Electric circuitry has quite the contrary effect. It involves in depth. It merges the individual and the mass environment. (…) The awareness and opposition of the individual are in these circumstances as irrelevant as they are futile.  (Through the Vanishing Point, 244)

In contrast to Marchand’s take, McLuhan started from ‘The Gutenberg Galaxy Reconfigured’⁴ and pointed to an “anti-hero” whose heroism has not only been broken but “has gone through the vanishing  point”:

The anti-hero became a theme in art and literature as early as Thackeray’s Vanity Fair, the “novel without a hero.” (…) The heroism of New England’s Pilgrim Fathers has gone through the vanishing point. (Take Today, 207)

“The vanishing point” is the utter extinction of the hero because the hero cannot survive the “vanishing” of his or her external — and associated internal — ‘landscape’. Where Marchand writes of “the vortex of threatening social change”, McLuhan was clear that the twin aspects of the “psychic and social environment” (Through the Vanishing Point, 12) rise and fall only together:

the slightest shift in the level of visual intensity produces a subtle modulation in our sense of ourselves, both private and corporate. (Through the Vanishing Point, 238)

As the Western world goes Oriental on its inner trip with electric circuitry (…) the whole nature of self-identity enters a state of crisis. (Through the Vanishing Point, 254)

The new hero is a corporate rather than a private individual figure.  (Through the Vanishing Point, 260)

Marchand’s “hero” is able to take “detached observation of the vortex”. But for McLuhan:

[only] the “objectivist” supposes that he can stand naked “out of this world.”  (The Argument: Causality in the Electric World, 1973)

For him, a collapsing environment collapsed such objectivity along with it:

Their [observers like Marchand] hidden hang-up was the visual bias of all “objectivity,” whether “materialist” or “idealist.” They also ignored the acoustic “message of the birds” — the output of any process, biological or psychic, always differs qualitatively from the input. There are no “through-puts” or connections between processes but only gaps or interfaces for “keeping in touch” with “where the action is.” (The Argument: Causality in the Electric World, 1973)

In his ‘Descent into the Maelstrom’ the mariner is just such a processing of (gen obj!) his own self!⁵ The “output” of himself “differs qualitatively from the input” of himself.  His own being —  he himself — is what is at stake in this knotted (and notted) process of trans-formation!  Between his input ‘down’ state (‘Descent into the Maelstrom’) and his output ‘up’ state (‘Ascent from the Maelstrom’) “there are no ‘through-puts’ or connections between processes but only gaps or interfaces”.

Such a transitive gap in identity via “vanishing” is what Poe calls “the incomprehensible mechanism” and this is the one starting point or “threshold“, among the plurality or spectrum of possible thresholds, from which any fitting consideration of McLuhan’s work must make its start:

New environments reset our sensory thresholds. These, in turn, alter our outlook and expectations. The need of our time is for a means of measuring sensory thresholds and a means of discovering exactly what changes occur in these thresholds (Through the Vanishing Point, 253) 

Thresholds have us, not we them.⁶ Their spectrum constitutes a kind of psychological and ontological Maelstrom whose navigation “demands awareness that can be achieved only by going Through the Vanishing Point.”