What's the difference between role-playing games and other mediums? The audience is the same as the actors. The players fill both roles. But for the players to face interesting challenges they are usually kept in the dark about more things than a passive audience needs to be. An audience at a movie can know who the murderer is from the start and sit in suspense as the protagonist unwittingly turns their back on the killer. If the players knew that from the start they wouldn't have much of a challenge solving the mystery.
In a movie or story other information is revealed to the audience to give the story perspective, even if the protagonists don't see it. The audience sees the night watchman get pounced on from the shadows, revealing that all is not well in this small town. The audience sees the comet impact outside town, heralding the arrival of the alien zombie virus. But players have a first-person perspective through the eyes of their characters so by definition they only see things that their characters see. They are never shown background action that would put the story in perspective or foreshadow events.
One alternative is to manipulate the scene unnaturally so the PCs are participants or observers in these situations, which defies internal logic, or to have the events reported by a third party NPC, which… would be… boring.
A better solution is NormalVision: players temporary take on the roles of characters who would normally be inconsequential NPCs. By playing these mundane characters, the players get to participate in events that their main characters would never see first-hand.
NormalVision characters are not heroes or protagonists. They are extras, red-shirts, background characters in the great scheme of things. They are the doomed nightwatchmen, the curious teens at look-out point, the native graverobbers who disturb a tomb that should not be disturbed. In other words, they are normal people (except perhaps for the circumstances they find themselves in), and the players see the world through their eyes, at least for a little while.
NormalVision is a departure from ordinary play because the players are not expected to be the ones setting the direction of the scene. They should not be trying to change the course of the action. This might be hard for some players (or GMs) to get.
By definition, NormalVision characters may be doomed from the start. If the players are taking on the role of a freighter's crew far out to sea, and the point of the scene is to reveal that some mysterious menance is destroying ships, the NormalVision PCs are not likely to survive when their vessel is attacked. They won't even be able to put up a fight. The scene can pretty much fade to black as soon as the unseen terror strikes from beneath the waves, except for a cut screen of the sinking ship.
An advantage of NormalVision is specifically that it delivers information to the players not the characters. The players may know that something strange is afoot, but since they know their characters do not they can comfortably continue to not expect the unexpected. It clarifies the boundaries of metagaming, freeing up the players to manuever their characters in a way that fits the theme of the game but still enjoy their ignorance.
As a role-playing exercise NormalVision can be challenging and fun. It lets the players experiment with a new role for a short time. They get to improv and try new ideas with no long term repercussions. The change of pace can be quite refreshing, shaking players out of their regular roles.
Coming Soon, NormalVision (part 2), When Should I Use It?