The purpose of SVV (Subjective Visual Vertical) is to detect abnormal subjective tilt. In normal persons, the ability to perceive verticality is quite good. This ability is dependent on visual, vestibular (otolith system) , somatosensory and central nervous system.
The SVV requires a remote controller for audio or video playback. Instead of the remote controller, you can also tap left, center, and right of the screen.