How do we create a mental model?
Mental models are, like the word says, entities that live in our minds. They are created by observing reality and taking away only the important details, in a cycle that looks something like "Observation -> Distillation -> Application of the model -> Observation" and so on.
The observation phase is where our mind fills with all the necessary details to create the model, or at least the details that seem important. In fact the same situation can have different models based on the ultimate goal that we intend to achieve at the time of examination. Let's think, for example, of a situation in which we want to find a barber shop in an unknown urban area. The shop windows must be decoded to find one that matches our idea of a barber shop. If we were to find a big concert though, the sound cues would be a much better information compared to the visual signs, to track where the concert is.
In videogames, the ultimate goal of the game itself defines the necessary information that the player must get from the game world. This is why feedback and User Interface is so important in games: for the player to build a model of the game world, he must have all the necessary information during play. Because he only has a limited time to obtain them (he lives in the game world only for some hours) the vital informations must be presented in the best possible way, and not cluttered with unuseful bits of knowledge, unless the target of the game is to confuse the player by purpose with this information overflow (like in detective games).
Going back to PES for Wii, the designers devised a great arrows and icons sign system to provide the player with all the information she needs. For instance, each time the human player orders a shoot by shaking the nunchuck and the ball is loose, a red diamond pops on the head of the nearest player on the field. In defence, the same command orders the nearest player to clear the ball, and a blue icon pops up. Colors, iconic graphics and sounds are always the best ally when a designer is creating a model that he wants to be easy to read.
While the great deal of icons and arrows on-screen might seem an unnecessary feature, it's actually a simplified mental models that the developers provided for the player to better digest the game.
The right way
We sometimes also see games who add real-life aspects to a game. Sometimes this is done deliberately, giving frustration because the player has to keep in mind aspects which are not really related to the goal, or the ways to achieve it. Other times this is done in an efficient and effective way.
Let's take Gears of War cover system as an example. A much praised feature, it's surely a step forward that the game takes towards reality, but if we look closely to it uses the same model defined structure that we talked about at the beginning.
In the game you can't press a button to cover behind everything (like you would do in real life), instead the developers chose to clearly emphasize objects which can be used as cover. This is done by displaying an iconic graphic that is overlayed on the game world.
They mapped a button to it, to make it easy and secure: you are either under cover, or not. Besides, you don't have to turn your back to the cover or duck before. As it was not enough, when you can cover yourself behind something you see a 'cover icon' that also tells which button to press.
Going further, they also placed covers in key points, maybe just before the coming of some enemies. This gives the player the knowledge that if an enemy is coming, he surely can hide behind something (90% of the time).
This way, taking cover becomes part of the mental model of shootings in Gears of War in a very simple and effective manner: it's a very clear action, you are covered or not, the only thing to do is to press a button. Reality is here, in a distilled form.
So as always in this case there's no dos and don'ts. Adding 'unnecessary' or out-of-reality features to a game is always a perilous process, but as you can see it can actually add to a game if done the right way. Sometimes it can also lead to an entirely new conception of an aging game genre, bringing some fresh perspective to it.
The message here is to always try to distill the action that we want to put in the game, and see if it fits the mental model that a gamer could possibily build on top of the game itself. Is it ok? How can we rethink the game instead, to make space for this new action?
The game designer must always be very wary of the mental model of his game, trying to anticipate the one made by the player so both can possibly match as much as possible with each other.