Created by Mickey Fisher, the future-set show stars Halle Berry as an astronaut who returns to her family after a year in outer space.
Asked about the extent of Spielberg's involvement in Extant, Walker replied, "Well, very involved in the very beginning.
"I mean, even before I was involved, he read Mickey's script and responded to it. And he kind of brought it under his roof there at Amblin Television and brought Mickey in. And then I joined up. And then we went and went out and pitched it," Walker recalled. "But every step of the way, from the creation of the world after what... you know, the extension of the world post-Mickey's pilot, and through every character's development and all the season-long arcs, we consulted with Steven and had long conversations with him."
Co-starring Goran Visnjic, Camryn Manheim and Grace Gummer, Extant is to premiere July 9 on CBS.