The brain needs to create a model of a constant pulse ― a schema ― so that we know when the musicians are not conforming to it. This is similar to variations of a melody: We need to have a mental representation of what the melody is in order to know ― and appreciate ― when the musician is taking liberties with it. Metrical extraction, knowing what the pulse is and when we expect it to occur, is a crucial part of musical emotion. Music communicates to us emotionally through systematic violations of expectations. These violations can occur in any domain ― the domain of pitch, rhythm, tempo, and so on ― but occur they must. Music is organized sound, but the organization has to involve some element of the unexpected or it is emotionally flat and robotic. Too much organization may technically still be music, but it would be music that no one wants to listen to.