history of - What is the first reference in Sci-Fi to a touch-screen computer interface?

Well I had a nice write up about The Guide in Hitchikers Guide to the galaxy (due to the amount of blogs and articles which mentioned it) which predated TNG but I happened to find this link from another scifi question: Fictional origins of touch and gesture technology

So I investigated about the "opton" (mentioned by DVK) from Return from the Stars(1961), by Stanislaw Lemand it turns out it is uses a touch interface. Here is a quote from the book since that answer didn't mention it:

Chapeter 3:

The bookstore
resembled, instead, an electronic laboratory. The books were crystals with recorded contents.
They could be read with the aid of an opton, which was similar to a book but had only one page
between the covers. At a touch, successive pages of the text appeared on it. But optons were little
used, the sales-robot told me

And I found an even earlier example in Issac Asimov's Foundation(1951) with the "calculator pad"

Chapter 4:

"Before you are done with me, young man, you will learn to apply psychohistory to all problems
as a matter of course. –Observe." Seldon removed his calculator pad from the pouch at his
belt. Men said he kept one beneath his pillow for use in moments of wakefulness. Its gray,
glossy finish was slightly worn by use. Seldon's nimble fingers, spotted now with age, played
along the files and rows of buttons that filled its surface. Red symbols glowed out from the
upper tier.

Also mentioned in one of the answers (by DJClayworth) is a non-fiction example, the "memex", described in As We May Think by Vannevar Bush in 1945
http://www.theatlantic.com/magazine/archive/1945/07/as-we-may-think/303881/?single_page=true

And his trails do not fade. Several years later, his talk with a friend turns to the queer ways in which a people resist innovations, even of vital interest. He has an example, in the fact that the outraged Europeans still failed to adopt the Turkish bow. In fact he has a trail on it. A touch brings up the code book. Tapping a few keys projects the head of the trail. A lever runs through it at will, stopping at interesting items, going off on side excursions. It is an interesting trail, pertinent to the discussion. So he sets a reproducer in action, photographs the whole trail out, and passes it to his friend for insertion in his own memex, there to be linked into the more general trail.