Watching it now. Every time I see it I keep trying to work out how Poltergeist was able to fly by without giving any type of credit to Richard Matheson. Works with less similarities--I'm thinking Ellison and The Terminator--have led to settlements and later credits.
http://www.poltergeist.poltergeistiii.com/wrote.html
"[There were] suspicions that Spielberg had been heavily influenced by Richard Matheson's short story and later "Twilight Zone" episode "Little Girl Lost." [Season 3, Episode 26, March 16, 1962]
In fact, in a 1982 interview with "Twilight Zone" magazine, Matheson stated that Spielberg had once shown an interest in adapting that story as a film. It would later be rumored (but not confirmed) that Matheson was hired to write the "Twilight Zone" movie (and given a percentage of that film's box office) partly in an effort to head off any potential suit over "Poltergeist."
"...Matheson: Well, POLTERGEIST was inspired by one of mine, and I never got credit for it. Matheson: Well, I don’t even know if using “Little Girl Lost,” and kind of taking some of it for POLTERGEIST… god, he must have felt guilty or something. Because he hired me as the creative consultant on AMAZING STORIES, and I didn’t do too well on that..."
"But he called me and sent me a copy of the script for REEL STEEL, although as I recall it was not the same as it was in the movie. He asked me “Does it resemble your script for STEEL?” It did, and I told him so. So then they paid me money for it, which they probably wouldn’t have done otherwise...Yeah, I have an odd relationship with Steven.....But we have always had a very amiable relationship."