Here's a video showing the variety of video imagery of the three Critter & Guitari video synthesizers responding to the same audio source!
The Video Scope (top left quadrant) is an oscilloscope. It displays the waveform of the audio you send to it. Depending on the mode, you can control the waveform's color, width and/or color switching rate..
The Rhythm Scope (top right quadrant) displays elemental patterns that change with each sonic 'event'. An event may be just a loud 'peak' of noise, or it may be something more musical like a drum beat or arpeggiated note.
The Black & White Video Scope (bottom right quadrant) has both oscilloscope and rhythmic pattern modes.
In each video synth, one knob selects the mode or parameter and the other controls the gain of the incoming audio signal. (Another way to think about the gain knob is that it sets how sensitive the video synth is to the audio signal.)