Why does this require a new understanding of truth? That seems to me like giving up. We just need to accept that perception does not always (or even often) reflect the truth, and that perception can be easily manipulated.
I think accepting that is, in its own way a redefinition of truth for many.
It used to be that the truth was constrained by the information that gatekeepers in positions of power or media let us see, and all it took to be reasonably informed was to watch or listen to a reputable media outlet for half an hour in the evening, and ignore whatever they believed the bad outlet to be.
This masked the complexities of reality for most of the population.
The internet has exposed the turbulence beneath the surface of publicly accessible knowledge. Thanks to social media, the subjects of journalism can now respond to it, or head it off with nearly the same amount of reach as journalists themselves. The sane can be said of anybody with a half-formed opinion on anything.
Many journalists have seemingly gotten so busy responding to the gnats and the niggles, and the affronts to their authority that they didn't realize they'd been caught in the undertow (see Twitter and facebook's community's influence on what is/isn't covered).
This has become increasingly visible in their work, even as their platforms are being chipped away thanks to competition in an increasingly fragmented landscape with incentives aligned towards catering to increasingly niche constituencies.
As a result, the adversarial nature of our information landscape has been laid bare to a swaths of the public.
Does realigning our expectations as to where, how, and if we'll find the truth redefine it? Not literally. But from a cultural perspective it does.
For the better? I don't know. I doubt it. Esp. in the US, too many of us weren't prepared to operate in such an environment and we're culturally already predisposed to conspiratorial thinking (rich coming from me). But it's where we're at right now.
An academic philosopher once handed me a (pre-1970s) hardbound book called Observation and Interpretation. I don't remember the author or the book's content (anyone know??), but the title suggests a powerful distinction and a tool for thinking about these questions.
Observations ('sense data' and personally-acquired life experience) are what we can (conceivably at least) fully agree on. 'Sam has hair'. 'Don't kick boulders.' Those upon which we can agree are the foundations of (that terribly-abused word) 'truth'.
We need to careful about using the word 'perception' as a stand-in for 'interpretation'. When we talk, we agree to pretend that we understand what each of us is saying. But when the words from my reality-tunnel cross the threshold of your reality-tunnel, your ears will likely hear my sounds, but then your brain interprets them. Danger, Will Robinson!
