Masked objects provide a "portal" into the cage regardless of motion. As long as Motion Settings are turned on, the vignette will also fade in the cage in the user's periphery upon movement.

TIP: To use in this manner, masked objects should be in world space, not affected by player motion.

This is primarily used to create portals fixed in the world, so the cage is seen "through" the world. This can help the user ignore motion by establishing the cage as a constant static background.

TIP: This creates the effect described in this Oculus blog post under the heading Portals Into the Static World.

This is the inverse of WINDOW Mode where masked objects show the world, not the cage.

PORTAL mode. Portal objects in the scene have the VRTPMask component attached. The vignette fades in at the periphery due to the motion settings.