So rather than go the full CGI route with the scenes set in OASIS, Steven Spielberg opted to make full use of his actors by having them act out the scenes in motion capture, which sounds like a wise course of action.
Steven Spielberg already has plenty of motion capture experience with The Adventures of Tintin and The BFG, and even though these characters are being represented in the virtual world by avatars, their movements and actions will look much more realistic.
Tye Sheridan, who right now is best known for playing Cyclops in X-Men: Apocalypse, also mentioned beforehand in this Collider interview that roughly 60% of Ready Player One will take place in the OASIS, with the remaining 40% set in the normal world.