Don't know that there is an exact switch. But for some it's verbal. If you know what it is that gets them going you turn the talk in that direction, then pull the trigger. I had a girlfriend that liked to be told what to do and got wilder the more I told her what a hot slut she was and smacked her ass. I left hand prints, and she wanted more. She was a bit of a psycho though.
Not the same trigger for all but they all have one.