There is a very real disconnect between training and what actually happens during a deadly force confrontation involving a firearm - specifically in a legal defensive gun use by a ccw citizen or LEO.
Personally I have experienced nearly every sort of adrenaline related handicap from slow/matrix motion to audible exclusive and especially tunnel vision. There are two things I have learned will definitely happen during these types of events, #1 is you be affected in some physiological way and #2 is you will be on autopilot the entire time. The more of these events you experience the better you will be able to handle the adrenaline, but you will get it every single time. The more training you have for these types of events the faster and more accurately you will find yourself overcoming them.
Scanning and breathing are the #1 to break tunnel vision. Literally thinking about breathing and moving your head around and focusing on other things will break your tunnel vision and make your vision open up during a high adrenaline situation.
Specifically in reference to the OP, I have responded to numerous LE and ccw citizen involved shootings, many of which I participated in the investigation after the fact. I would say that the percentage of persons involved in a defensive shoot for the first time discharged their pistols one to three times and most impact points were around the hands/arms/chest where the hands (read weapon) would have been. One person I remember was knocked to the ground and shot the BG through the fist as it came down to hit him due to the age/size disparity.
Humans can only focus on one point accurately at one time, as such we are forced to choose what to focus on consciously all the time, we mostly do this autonomically, except when we are using the sights of a pistol. One question I ask LEO's and ccw citizens who have been involved in shoots is always if they actually saw the sights of their pistols and the answer is usually "no" to "only after the first or second shot." We train to use the sights, especially the front sights but people do not seem to actually do that. Or. Do those people actually see the front sight and simply do not remember they did due to adrenaline? I've been in that situation, especially in FoF, I do not consciously use my front sight by after reviewing video from different angles I have seen my eyes track my front sight and then discharge the sim gun. This was a huge learning point for me.
I believe that proper training will allow to go on auto pilot for the technical operation of the draw stroke and pistol use while leaving you to consider the tactical nature of the confrontation.