If the raw plot is the backbone of your story, the perception matrix, or perception framework, is the muscle that manipulates other elements of the story.

The perception matrix deals with when, how, and why each character is introduced, when and why certain plot highpoints should take place, which scenes should end on a cliffhanger, and how the characters are going to react to each other. These are all elements that you can use to manipulate your reader's experience. Or, in other words, the way in which you construct your book has an effect on the way the reader perceives the story.

Introducing the main protagonist

It is possible to freewrite without considering the perception matrix and even bestselling writers sometimes manage to do without it. For example, in Minette Walters' The Scold's Bridle, the first point of view character introduced to the reader is an unnamed policeman who observes the crime scene and the arrival of a detective in just a few paragraphs. This policeman is never mentioned in the book again and doesn't even get a line of dialogue to hand over to the detective. But it is the detective who turns out to be the real protagonist.

Meanwhile, the reader has begun the reading process with the traditional expectation that the first character introduced, and most certainly the first point of view character introduced, will be the main protagonist. When this proves false, it not only jars the reader out of the story, it makes the reader wary of accepting that book's matrix at face value, and, therefore, settling into the book becomes that much more difficult. Walters could easily have avoided this by taking a moment to consider her opening from the reader's perception rather than ploughing into it with no awareness of basic reader expectations.

It is important to remember that the main protagonist is the "vehicle" through whom the reader experiences the story. Even if your story has multiple viewpoints in between, the main protagonist should take the reader from beginning to end.