Over the years I've been asking people in my life who are old enough to remember which technological change felt more like a cathartic change to society: TV in the 1950s or the internet since 2000. Up until about 2006, everyone said TV. Since then – call me crazy, but I think it has to do with Google – it's been the internet and all its spawn: YouTube, smartphones, Facebook, apps … and everything else that jackhammers away at the time we once reserved for books, newspapers, daydreaming and, ironically, TV.

It feels wistful to imagine a time when people didn't go about their daily routine with the assumption that at any moment another massive media technology will be dumped on us by some geek in California. We really ought to give ourselves a collective pat on the back for doing as well as we have in a universe of constant media change and mutation.

Back at the start of TV people were thinking that it would be an excellent way to have puppet shows in the home. Other people got paranoid and their brains flew directly to Orwell, under the misguided assumption that any content on TV, being electronic, somehow bypassed the membrane of critical thinking we employ when reading a book; seeing would instantly become believing. Magazines would show cartoons of families watching TV with captions along the lines of: "The modern family: nobody communicating or interacting." (These days one might see that same cartoon with a caption along the lines of, "We miss the old days, when families did activities together, such as watching TV.")

And this is when Marshall McLuhan entered the collective imagination and became a huge media star. He did this either as a guru or as a villain – as a harbinger of the flowering of culture, or of its death. McLuhan was a fuddy-duddy fiftysomething English lit professor from Toronto. Through an alchemical mix of his vast historical and literary knowledge, his bombastic personality and a range of behaviors we might now place on the very mild end of the autistic spectrum, McLuhan was able to cut to the chase. He stated that the point of much of technology, TV, for instance, wasn't the content of the shows you were watching on it. Rather, what mattered was merely the fact that you were watching TV. The act of analysing the content of TV – or of other mediums – is either sentimental or it's beside the point.

Mediums change you by their very existence. They do this on fundamental levels because they force you to favour certain parts of your brain over others. To the person of 2011 this makes total sense. That hour you spent on Facebook came at the expense of some other way of using your brain, most likely TV viewing or book-reading, though as books and TV recede, ever more web-mediated activities will replace each other to the point where we'll have long forgotten what the pre-electronic mind was to begin with. And let's face it, Google isn't making us stupider, it's simply making us realise that omniscience is actually slightly boring.

To be fair, McLuhan was about more than "the medium is the message", but that remains a fabulous reduction. McLuhan was an information canary, warning us that there were new media coming down the line, and it was the effects of these new media on the mind that he wondered about so extravagantly – the message seemed to be very dark, indeed. Here's what he wrote in 1962, and see if it doesn't give you a chill: "The next medium, whatever it is – it may be the extension of consciousness – will include television as its content, not as its environment. A computer as a research and communication instrument could enhance retrieval, obsolesce mass library organisation, retrieve the individual's encyclopedic function and flip it into a private line to speedily tailored data of a saleable kind."Brrrrr.

The medium is the message seems like a timeworn cliche, yet in recent years it has flipped and become one of the most germane of statements. In his poetic and elliptical ways, McLuhan foresaw a fluid melting world of texting, email, YouTube, Google, smartphones and reality TV. Most of the content of any of these media is pure crap. But what's spooking us all is the inevitable message of these new media: what will be the psychic fallout of these technologies on our inner lives?

Time seems to be going much faster than it once did. We don't remember numbers any more. Certain forms of storytelling aren't working for us as they once did. And what's happening to democracy? As with TV in the 1950s, don't be fooled by the content of texts or blogging or online shopping. Look at what these media are doing to our souls. That's what McLuhan did.