How has the evolution of the author centered, to the text, to the reader impacted the way we look at literature and truth?
There's a fine line between seeing the author and his life as an overlay (or an underpinning, if you prefer) and assuming the story on paper is the author's story. However, knowing the author along with the historical context of the author and the work adds a richness to most reading experiences. I always stage the things we read with that kind of context, and it generally serves to add depth and interest for the students' experience. If the reader is all that matters, the truths are only personal and no longer applicable to something bigger and more significant. Anyone who reads literature in a vacuum is often missing out on an opportunity to discover timeless, universal truths and must settle only for personal truths--which is good, but it's not the best.
I think thanks to postmodernism and crucially to "The Death of the Author", authorial intention has, rightly or wrongly, been dismissed largely with a move towards our own interpretations of texts and in particular a focus on a plurality of truths which leaves texts open to ever-ending dissection. Personally, whilst I do find some aspects of this approach liberating, I think authorial intention needs to be given more emphasis. There appears to me to be a lack of respect in this approach that downplays the role of the author, whereas, to me, understanding the author has been richly rewarding when I come to trying to understand their work.
This is a big question. Theoretically, from a Reader-response theory perspective, the shift (20th century) has been to say the meaning of a text (truth in general) is not solely and absolutely created and maintained by an author or an "author-ity." This is part of an overall movement of challenging authority, but also a shift to the idea that reality is created in the mind of the observer. It is not analyzed by an expert (author) only to be communicated to the masses. This is at once, a challenge to authority, and a re-conceptualization of how we look at the world. I'm sure you could throw some physics in here too, like how light and observation actually affect what you're looking at. The same goes for literature. As you observe (read) it, you change it; at least in your own mind - your interpretation is necessarily different from the author's or any other reader's. This new way of looking at literature truth is not to replace the author's intent, historical analyses and so on. It is to supplement it. On the other hand, if you read Roland Barthes' "The Death of the Author," maybe it is that extreme. This death of the author is to liberate the reader; for all the reasons (and more) that I just mentioned.