In addition to the big ‘into the audience’ moments, for which the stereo team had to bring elements 300 to 400 pixels negative of the screen, the depth was also used more subtly, to distort what was happening on screen, adding to the general sense of unease.
There were a number of ways that the team used the 3D to distort the on-screen reality. They played with the depth budgeting way more than they would on other films. And used the 3D to stretch hallways and staircases away from characters so that it felt like they would never reach the end, however fast they ran. The team had fun with the glitch effects seen through the camera, leaving most of the shot flat but pulling the glitch effects out of the screen, super negative, to really unsettle the audience.