Motion Parallax: The relative movement of objects at different distances, resulting from the observer's own motion, which provides cues to depth.

Parallax This is a classic example of parallax (although this is fake parallax). You can create another example of parallax yourself. Hold you thumb out straight in front of your face at arms length.

Specifically, discomfort was due to a specific sensory cue called motion parallax, which is defined as the relative movement of different parts of the environment.