In the last couple of weeks, I've seen a few posts in forums for specific games with people outraged over there being no option to invert the mouse's vertical axis. In most cases, they say that it's the most logical way to control with the mouse. Which boggled my mind, because even though I invert the y-axis with joysticks, it's never even occurred to me to invert the vertical axis on a mouse.
I grew up playing flight sims (X-Wing vs TIE Fighter, which I used a joystick for) where "up is down" is the natural, logical way to control your craft. Even with first-person games, when I'm playing on a controller, I perceive the joystick as my character's head; pulling back on the stick translates to looking up with my character's eyes. With third-person games I invert the camera controls by default, because I envision an actual camera that I'm physically moving around to set up a frame.
But with a mouse, I've never inverted the vertical axis. It seems only natural that up would be up with a mouse. Unlike joysticks, the mouse moves on a flat plane; it doesn't move in a three-dimensional space. On the desktop screen, if you want to move your mouse cursor up, you move the mouse forward, and so if you want to aim the barrel of your gun up, you move the mouse forward. That's just the way I've always done it.
Can anyone actually justify why you would invert the vertical axis on the mouse, especially in a first-person game?