A common exercise while being in the back seat of a car while I was young was to imagine someone in a skateboard riding along the power lines on the side of the road, keeping pace with our car.
It's not literally overriding my vision, it's almost like a thin layer, less than transparent, over reality. But specifically, it's entirely in my mind. I would never confuse that imagery with reality...
Having said that, I think that is related to the way our brains process visual information. I've had an experience when I'm driving that, when I recognize where I am, coming from a new location in not familiar with, I feel like suddenly my vision expands in my peripheral vision. I think this is because my brain offloads processing to a faster mental model of the road because I'm familiar with it. I wonder if that extra "vision" is actually as ephemeral as my imagined skateboarder.