I acquired this concept from Heim (1999). The theory holds that the shifts in technologies that support language are at the root of tranformations in human thinking and, by consequence, civilization. In Electric Language, Heim explains and banks heavily on the general applicability of transformation theory to word processing technology, although he recognizes that it's not all positive, necessarily. In Heim's words, it is "the transformation theory of language technology or the theory of transformative writing technologies" (p. 49).
The history of transformation is recounted as the shift from oral/aural traditions, exemplified by the Homeric epic, to written or chirographic practice, and on through typographic and then electronic cultures. The principle notion is the rule of form and shared understanding in oral/aural culture because of, as I observe, the problem of confusing audiences by using grandiose explanations that critique existing forms. In those early days of orality, thinking about thinking was not a dominant public behaviour, so there was seldom the opportunity to break traditions that seemed to take hold readily. (This would necessarily be applicable to performance as opposed to deep conversation.) With the advent of written traditions and the recording of thoughts and ideas, and even previously oral texts, for thoughtful perusal and critical response, thinking could then be hoisted on conceptual frameworks. "The many writings of Walter Ong are firmly based on the premise he holds in common with havelock, namely, that a fundamental shift in the history of civilization occurred in the move from oral-aural information transmission to the paradigm of the literate mind (Heim, 1999, p. 57). This notion, thankfully, is also consistent with Clark, Pinker and Hofstadter.
But even chirography is an interpersonal experience that needed to be transformed by the introduction of typography, which creates a psychological distance between the personalities involved. Readers/critiques of printed materials can much more readily work with texts and their content as objects for intellectual scrutiny (1999, p. 58), although the early act of producing texts was still highly personalized. The final break came with electric language, the advent of computerized word processing tools and the concomitant separation of author and text.
One of the important aspects of transformation is the environment within which it operates. Heim speaks of media and communication as follows:
The term consciousness, because of its philosophical-historical connection with social theory, also seems to suggest that symbolic environments can be most properly understood to be forms of media or communication. Writing understood as a social medium for information storage and retrieval is a limited interpretation of symbolic environments. (1999, p. 101)
I take from this that Heim regards medium as a limited term. Neither I, nor Gardiner 2008, share this view. Mediation is not solely the transportation of information, but any intercession between a mind and the world.
Heim then goes on to raise transformation from mere phenomenon: "The transformation theory conceives the development of the human species as evolutionary" (1999, p. 102), which, however, does jibe with Gardiner's views of media shifts (2002).
(Personal Note: I'm having a ball playing these guys off one another.)
I'll stop here about transformation and leave readers to enjoy the first few chapters of Electric Language on their own terms.