I've played in several competitive tournaments myself and had a chess coach for a number of years. I don't know of any general studies or research (so I'll be interested if anyone finds anything more principled than my anecdotal evidence). In my experience, the main goal of chess coaching and training was to teach you how to act like you were a computer. Any kind of "intuitive" play or even creative play was harshly criticized from a young age. The first goal was to memorize a massive amount of opening theory and what is known as 'book' knowledge. Once a student has a reasonable amount of book knowledge, then you move on to techniques to focus you on calculating quickly.

In my later years, I've come to realize that the heuristics that chess teachers employ cause you to think in a way that's analogous to simulated annealing. You scan the board and make simulated "proposal" moves in your head, and in the early stages of your turn you should be very open (high temperature) to suggesting any move, no matter how preposterous, to yourself. But you also have to just very quickly look at the move's surface level consequences and basically classify it as "worth more of a look" or "worthless". You do this a few times, and assuming some independence of the distribution of your brain's ability to pick out decent moves, you'll have whittled down to maybe 5-10 respectable moves, and perhaps a few other riskier moves worth a second look.

At this point you really dive in deep and attempt to examine long chains of moves, maybe 5-6 moves deep for each of the 5-10 moves you've got going in your head. Your annealing temperature is much lower, so you're less likely to spend time thinking about weird variants or moves that don't have an obvious upside. You systematically focus on understanding two things, the immediate consequences of the moves and the level of complication each line of hypothetical play will bring about. The reason complication matters is that human chess is all about resource management. Given enough time, every player in the tournament is good enough to see the best moves, potentially even the best moves that a computer would see. The difference in human performance, though, is decision fatigue, carelessness, and inability to calculate long, complicated lines in memory (some kind of human cache limit, basically).

During this deeper analysis stage, you should ultimately come down to 3 moves that seem to be the best. For these moves, you'll go back over the 5-10 move sequences, maybe even up to 15 moves deep if you're a grandmaster, and you'll not only detect the complication, but also the larger strategic principles. Will having two bishops in this particular variation give you more mobility? Will your pawn structure effectively lock down your pieces? After the dust settles in a large exchange sequence, will your opponent have a passed pawn and can you stop it without losing a whole piece to babysit that pawn? Will there be pressure on the dark (or light) squares because of an exploitable tactic. From this, you eventually emerge with your chosen move.

There is also some meta-analysis that goes into it. Since you are analyzing the amount of complications expected in certain lines of play, you also develop some experience for knowing when the really critical points of the game are happening. You obviously cannot spend the effort of the paragraphs above on every single move. You have to miniaturize it and hurry it up for most moves, and to do that safely you need to be confident that you're not making fast moves in a deeply complicated portion of the game. This can be accomplished by studying lots of classical games, or by knowing a lot about your opponent's games and styles prior to a match, Most grandmasters will have only two or three moves per game that take longer than 15 minutes to make, but each of these will take 45+ minutes. If you spend 45 minutes on a move, you have to get more bang for your buck out of that move, so the subsequent moves should be able to go faster. If you spent 45 minutes on a move and then your opponent surprises you and you have to spend another large chunk of time, you're in trouble.

At any rate, my experience was that the nerves and the situation don't play much of a role at all because, if you have practiced well enough, you dive right into this deep Zen of computation, busily reducing the game down into the conscious simulation of a serial algorithm plus memory lookups, according to what your coach / training has taught you.