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.

TIP: Effect Color alpha controls opacity of the world, not the effect. This can be used to partially overlay a cage or cubemap over the entire view.

PORTAL mode with cage and motion. Portal objects in the scene have the TunnellingMaskObject script attached. The vignette fades in at the periphery due to the motion settings.